Black Bittern

Ixobrychus flavicollis (Latham)

Ardea flavicollis Latham, 1790. Index orn., 2, p. 701: India.

Subspecies: Ixobrychus flavicollis australis (Lesson), 1831: Timor; Ixobrychus flavicollis woodfordi (Ogilvie-Grant), 1888: Solomon Isles, Aloa.

Other names: Yellow-necked Bittern, Mangrove Bittern in English; Avetorillo Negro in Spanish; Blongios à cou jaune in French; Schwarzdommel in German; Takasago-kuro-sagi in Japanese; Mangansile in Pilipino (Philippines); Kokokan sungai in Indonesian; Hei Yan in Chinese.

Description

The Black Bittern is a medium black or dark brown heron with a brown and white striped throat bordered by yellow.

Adult: In the male, the head and hind neck are dark grey black with a blue sheen. The relatively long bill is dark but variable. The upper bill is dark brown to red brown. The lower bill is pale green or purple below, but sometimes suffused with a reddish tinge with a yellowish tip. The irises are yellow to red brown and the skin around the eye is variable, dusky to green or pink. The chin, throat, neck and upper breast are deep buff streaked with black and white and bordered on each side by a paler gold yellow band from the chin to the base of the neck. A loose tuft of elongated feathers on the foreneck overhangs the upper breast. The back, tail and upper wing are grey black, with the wing coverts tipped in buff. The under parts are dark grey brown, often with a yellow wash. The legs are variable black, dark brown, or olive green with yellow green soles.

Variation: The female is slightly paler, generally brown grey instead of dark grey black, with more yellow wash to under parts. The female also has throat, foreneck, upper breast streaked with yellow, white and black with yellow breast plumes.

Birds vary individually and geographically. Individual variation is great. In Australasia, six plumage morphs have been recognized (Mayr 1945). All black and mostly white individuals have also been found (Payne and Risley 1978).

Described geographic variation is ascribed to three subspecies. Flavicollis, as described above, has the least amount of plumage variation. Compared to flavicollis, australis tends to be larger and variable. Males from Bismarck archipelago are mostly black with brown streaking on the throat and some females have brown grey under parts. Other morphs have been reported within this subspecies’ range. Compared to australis, woodfordi is slightly smaller, has a relatively longer bill, and males are darker below with narrow white streaks on breast and foreneck. Patterns of geographic variation are not clear given the vast amount of individual variation in the species.

Juvenile: The immature bird has a grey black crown, but appears duller with a rufous wash. The breast is brown streaked in yellow. Back feathers are edged in buff. Lores are green brown. Irises are yellow. Legs and feet are brown grey.

Chick: The downy chick is white with light brown tinge to neck and rump. The irises are black brown becoming dark brown. Bill, lores, legs and feet are light pink.

Voice: The “Whoo” is a low booming drum like call, a peculiarity of this species among the Ixobrychus bitterns. It is long, drawn out, rendered “ wh, o, o, o, o, o, o”, given at 15 s intervals and answered by neighboring birds. It undoubtedly is a territorial and advertising call. A soft “coo-oorh” call is given approaching the nest. Other calls have been reported but need to be clarified.

Weights and measurements: Length: Very variable, 55-65 cm. Weight: 275-358 g.

Field characters

The Black Bittern is identified by its size, dark back, striped neck bordered by a striking yellow streak, and its long bill. It is usually seen flying away into thick cover. It is distinguished from the other Ixobrychus bitterns by its dark back color with yellow neck and its larger size. It is distinguished from the Gorsachius night herons and the New Guinea Tiger-Heron by its uniformly dark plumage and disproportionately long dagger-like bill. It is distinguished from the Green Backed Heron by its uniformly dark upper parts, yellow patch and breast stripes.

Systematics

The Black Bittern is one of the Ixobrychus bitterns, but is the largest of the group. It is similar morphologically but uniquely has a booming call (Payne and Risley 1976). It also has a distinctive skull shape, related to its very long bill. It was previously assigned its own genus. Its skull and color pattern are most similar to the Dwarf Bittern.

Range and status

RANGE: The Black Bittern occurs in India, Southeast Asia, Indonesia, Philippines, Australia, New Guinea to the Solomon Islands.

Breeding range: The breeding range of flavicollis is Pakistan (Sindh), India (Jamdar and Srivastava 1990), Maldives, Nepal, Sri Lanka, Bangladesh, Myanmar, Thailand (Round 1992b, 1995, Lansdown et al. 2000), Cambodia, Vietnam, to central and south China (Yunnan, Hainan, Guangdong, Fujian, Taiwan, Hubei, Anhui, Shanxi), Malaysia (Sabah, Sarawak, Indonesia (Sumatra, Timo), Philippines. Australis occurs in Indonesia (Moluccas, Irian Jaya), Papua-New Guinea (including Bismarck archipelago), coastal Australia (north Queensland to New South Wales – Morris 1971). Woodfordi is confined to the Solomon Islands.

Nonbreeding range: Northern populations in China are migratory, wintering in western Malaya (peninsular, Sarawak), through Indonesia (Lesser Sunda Islands), and Philippines. There has been no recorded breeding in south west Western Australia since the 1950’s (Marchant and Higgins 1990).

Migration: Chinese birds move south in October to peninsular Malaysia, Greater Sundas and Philippines. Return is April- May. Post-breeding dispersal occurs and is likely the origin of island populations of this species. In India post breeding dispersal and drought based movements occur. A Malaysian bird has been recovered in India (Manipur) and an Indian bird was recovered in Maldives. Australian birds appear to be sedentary, but some regional movements occur. Dispersal records include Japan (Fukumoto et al. 1992), Christmas Island (Indian Ocean), Mollucas, Guam (United States).

Status: The status of the species is unclear. It is common in Pakistan, parts of India, and Sri Lanka. It is common and abundant in Myanmar and southeast China (Lansdown et al. 2000). It is widespread and not uncommon in east Australia but has declined over the past 50 years due to destruction of river edge habitat for farming, pastures and also because of salinization (Marchant and Higgins 1990, Maddox 2000). It is common in winter in Sarawak (Malaysia). It is uncommon in winter in Sumatra (Indonesia) and Philippines. It is widespread in New Guinea.

Habitat

This species typically uses thick scrubby vegetation, particularly forested streams and pools in permanent wetlands. But it uses a variety of habitats including swamps, mud flats, reed beds, wet forests, flooded bushy areas, marshes, forested streams, Pandanus fringed channels in swamps, Melaleuca swamps and coastal mangroves in Australia. Although primarily a lowland species, it occurs up to 1,200 m in India. It winters in reed beds around lagoons, pools and reservoirs in peninsular Malaysia and Borneo. It uses trees and reeds to rest and roost.

Foraging

The Black Bittern forages singly or as a pair in thick vegetation. It feeds by Standing with its neck and head pulled in and by Walking Slowly in Crouched or Upright postures (Recher et al. 1983). It also can scuttle agilely along mangrove roots and creep stealthily in a distinctive crouch. It feeds crepuscularly and also during the day when it is overcast or rainy.

They are seldom seen because they hunt in densely vegetated marshes and creek edges. When disturbed, it runs into cover or flies away. They roost when not foraging in reeds, trees or on the ground.

Food items recorded include relatively large fish, 12 to 115 cm long (Perca, Amniataba, Gobiomorphus), frogs, lizards, crabs, crayfish, shrimp, mussels, and insects including dragonflies, beetles, and flies.

Breeding

Nesting timing differs geographically. In the north, breeding is triggered by the advent of the monsoon, at any time between May and September. In Sri Lanka nests have been found in April, May in Java, February in New Guinea, and September to January In Australia. Overall it breeds in densely vegetated, secluded wetlands. But its nesting habitat is surprisingly diverse, depending mostly on having dense cover near water. In India and Sri Lanka, it nests in reeds, thorn bush or cane breaks low over water. In China, it nests in bamboo and trees as high as 6 m. In Australia nests are located in gums standing in water and in mangroves. It occasionally nests away from water and is it not unusual to nest close to human habitation.

Black Bitterns nest solitarily or in loose nesting groups. At places the nest interspersed in mixed colonies with other herons. The nest is a platform, 23-35 cm wide and 7.5 cm, with a shallow central depression. It is made of twigs or reeds. The nest is built by both birds. Its placement is variable, from 1 to 15 m above the water or ground.

Little is known about the courtship of this species. It adopts the Bittern posture when disturbed and when alarmed, raises and lowers its crest. It is likely that the plumes at the base of the neck are used during courtship display, but there is no information.

The eggs are white, although there have been reports of a blue tinge to some. As recorded, they vary in size averaging 41.6 x 31.4 mm in India and Myanmar, 45 x 35 mm in Australia, and 43 x 34 mm in New Guinea. Clutch size is 3-6 eggs. Although it is probably usually single brooded, double broods occur. Incubation is by both sexes. Both sexes feed the chicks regurgitated food. The incubating bird sits very tightly and the chicks. The chicks soon leave the nest if disturbed.
Nothing is known about late nesting.

Population dynamics

Nothing is known of the population biology and demography of this species.

Conservation

In Australia the species has declined owing to clearing for agriculture and the increasing salinity of the rivers. It was once common in southwest Western Australia but is not known to have bred there in 50 years. It is widespread elsewhere in Australia, but Garnett (1992) listed it under Taxa of Special Concern. In NSW it is listed (updated 1999) as Vulnerable under the NSW Scientific Committee Threatened Species Conservation Act 1995 and in Victoria its conservation status is classified as Critically Endangered (NRE 2000). The actual breeding distribution is little understood and not quantified. In many cases the range is based on a few observations. A basic conservation need is to clarify the breeding locations and distribution of the species and to locate the most important breeding areas.

Research needs

Patterns of geographic and individual variation are not clear. The variation in plumage and size in this species needs to be re-examined. There also is a need to clarify the status of the species throughout its range.

Overview

The Black Bittern is a forest bittern, a bird of thick cover, generally scrubby vegetation along mangrove shores and other watercourses. It is not a river heron in the sense of using running water, but thick vegetation along water courses appears to be a habitat requirement. It feeds in normal bittern fashion, but is relatively large for a ‘small' bittern. With its long bill and neck, it appears to be a fishing heron, working along the banks of watercourses from vegetation. It appears to take relatively large prey, and so may not eat large numbers of prey items per day. It likely feeds from territories, which it knows well and undoubtedly defends. Much remains to be learned about this heron.

Dwarf Bittern

Ixobrychus sturmii (Wagler)

Ardea sturmii Wagler, 1827. Syst. Av., Ardea, No. 37: Senegambia.

Other names: Rail Heron, African Dwarf Bittern in English; Avetorillo Plomizo in Spanish; Blongios de Sturm in French; Graurückendommel in German.

Description

The Dwarf Bittern is a very small, dark heron with dark and buff stripped throat and under sides.

Adult: The male has a dark slate grey head and neck, with elongated head and neck feathers. Bill is dark. The upper bill is black to dark green. The lower bill is yellow. Lores and orbital skin are blue to yellow green. Irises are red brown to dark red. The back, upper wings and other upper parts are dark slate grey. Its throat and upper breast are pale buff, darkening to tawny on the abdomen, heavily streaked black. Legs and feet are green yellow in front and yellow in back. In courtship legs and feet turn bright orange.

Variation: The female is paler, with a more rufous tinge on its belly and yellow irises.

Juvenile: The immature bird is more buff and pale than adult. The buff tips to the wing covert feathers. Its under parts are more russet. Its foreneck has narrower streaking. Bill is dull yellow grey. Irises are orange red and the legs and feet are yellow.

Chick: The down of the chick is ginger brown, slightly longer on the crown creating a crest. The irises are dark brown. The skin, bill, legs and feet are pink.

Voice: The voice of this species is little known. A loud croak is uttered when disturbed.

Weights and measurements: Length: 27-30 cm. Weight: 142 g.

Field characters

The Dwarf Bittern is identified by is uniformly dark upper sides, streaked under sides, and yellow feet. Its flight is slow and labored. The bird is most often encountered flying into the bushes when disturbed.

It is distinguished from the Black Bittern of Asia by its striped belly, dark neck tufts, shorter, darker bill and much smaller size. It is distinguished from the Green Backed Heron by its smaller size and slow flight, its pale and heavily streaked underparts, and its uniform (not barred) upper parts.

Systematics

The Dwarf Bittern is one of the small bitterns, Ixobrychus, which share similar plumage, white eggs, scutellate tarsi, and ten tail feathers. The species is unusual among the small bitterns in having only a slight sexual dimorphism. It was once placed in a genus of its own (Payne and Risley 1976).

Range and status

The species ranges throughout much of Africa south of the Sahara, except for deserts.

Breeding range: It breeds occurs from Senegal, Ghana, to Sudan, south west Ethiopia, south Somalia, Kenyan, Tanzania (one record), south east Zaire, Zimbabwe, south Mozambique, Namibia, north east South Africa.

Nonbreeding range: Birds occur in tropical Africa during the northern and southern nonbreeding dry season.

Migration: This is a migratory species within Africa, particularly in the north and south. Movements of equatorial birds are less clear. Birds occur in South Africa in the November–April wet season. In the dry season, birds from both north and south the migrate toward the equator (Brown et al. 1982). The species does wander outside its usual range, including further into South Africa (Ingram 1998), Canary Islands, and France.

Status: The species is widespread but rare to uncommon range wide. It does become more obvious and common at breeding sites, such as in Namibia, and south Angola.

Habitat

The Dwarf Bitter uses a variety of habitats, but generally characterized by fluctuating water levels. Habitats include the margins of flood plain rivers and seasonal pans. It also uses fresh water river pools and, especially, edges of creeks, rivers and streams overhung by dense foliage, rice fields, roadside pools, open grassy swamps, lake islands, cat tail marshes and papyrus. It nests in thickets and trees, such as Combretum, Ziziphus, Terminalia, and Diospiros (Hustler and Williamson 1985), near its feeding area.

Foraging

Dwarf Bitterns feed solitarily or in pairs, hunting by night and ,especially if it is cloudy, by day. This it does silently and unobtrusively by Standing and by Walking Slowly. This daily schedule overlaps availability of frogs (Tarboton 1980, Hustler and Williamson 1985). Dwarf Bitterns sometimes prefer to sneak through vegetation and reeds rather than climb or perch on them. When disturbed they stay put at the water’s edge in an exaggerated version of the Bittern posture or it often fly up into trees moving only short distances. It is likely that individuals defend feeding territory, and its use of a Forward display has been described (Riddell 1987).

Insects, such as grasshoppers and water bugs, spiders, small fish, crabs, snails and frogs form the main items of the diet. Local populations specialize in grasshoppers and frogs, and can take advantage of seasonal prey availability such as frogs in fishless seasonal pans (Hustler and Williamson 1985).

Breeding

Breeding season is highly variable geographically. It nests primarily in the rains, but in some places in the early dry season. Nesting begins in September in Senegal, July in Sierra Leone and Ghana, August–October in Mali, December–January in Zaire, May–June in Kenya, January–March and September–October in Zimbabwe, February–March in Namibia, and January–April and September–December in South Africa.

It nests along the margins of flood plains, usually when the water inundates the forests. It appears to prefer thicket vegetation in which it nests solitarily or in small groups. Although not usual, they have been seen to nest near Squacco Heron and Rufous Bellied Heron. The nest is a platform of twigs lined with coarse grass, 23 x 38 cm across and 7 cm deep. The nest is placed near the central trunk of the tree, on a branch or in bushes overhanging the water. Height is 0.5-4 m above the water. They often use thorn bushes for nesting. It builds its nest quickly (Tarboton 1980).

Courtship behavior is not known. The eggs are white. Some fresh eggs are faint blue, but this fades within days (Hustler and Williamson 1985). Eggs are about 34 x 28 mm. Clutches are 3-4 eggs, range is 2-5 eggs (Hustler and Williamson 1985). Incubation is 18 days and longer. Nests have not been reported with asynchronously hatched young, so it is possible that incubation begins with the last eggs (Hustler and Williamson 1985).

The young are fed by regurgitation in the evening. They develop quickly. At seven days they leave the nest if disturbed, but return. When fully feathered they wander widely. When sitting on a branch, they adopt a Bittern Posture and are hard to see. In one study only 69% of eggs hatched (Hustler and Williamson 1985).

Population dynamics

There is no information on population biology or demography of this species.

Conservation

The species is uncommon but also is widespread. Information is limited, and the most important conservation measure is to increase our knowledge of the species.

Research needs

The biology and behaviour of the species is relatively unknown. There is a particular need for a better understanding of its seasonal movements and its nesting and non-breeding distribution. The suggestion that this is a species adapted to take advantage of ephemeral food resources made available by rain and fluctuating water levels should be studied further. This is a species for which a satellite transmitter study of individual birds could provide important information to clarify its continent-wide movements. Seasonal, individual, sexual, and developmental changes in soft-part colours are poorly understood. Additional study is needed to assess these individual differences.

Overview

The Dwarf Bittern is a forest bittern, and one that appears to be to take advantage of ephemeral food supplies. One such habitat is seasonally flooded pans, which dry out in the dry season. When the rains come, birds find the pans. The bitterns build their nest and lay the clutch quickly, have a short incubation period, perhaps synchronous hatching, and chicks develop quickly and soon leave the nest. This nomadic tendency allows it to take advantage of both the predictable and unpredictable weather patterns that characterize Africa.

Cinnamon Bittern

Ixobrychus cinnamomeus (Gmelin)

Ardea cinnamomea Gmelin, 1789. Syst. Nat. 1(2), p. 643: China.

Other names: Chestnut Bittern in English; Avetorillo Canelo in Spanish; Blongios cannele in French; Zimtdommel in German; Ryukyu-yoshi-goi in Japanese; Bakaw-kanela, Lapay in Pilipino; Kekondangan, Kokokan in Indonesian; Li weiyan in Chinese.

Description

The Cinnamon Bittern is a small, predominantly rufous heron with paler under parts.

Adult: The crown, sides of head, nape, back, wings and tail of the adult male are cinnamon rufous. The bill is yellow to green orange with top edge horn. The lores are yellow. The irises are yellow to orange. The chin and throat are buff white, and a broad dark brown rather ragged median streak runs down the front of the neck. A tuft of loose black and dark brown feathers on the side of and at the base of the neck is expansible for display. The upper wing is rufous. The under wing is pink cinnamon to chestnut grey. The under parts are cinnamon buff, paler than the upper parts. Tail is chestnut brown. Legs are yellow green.

With onset of breeding soft-parts colors brighten, most markedly in the male. The iris has been described as yellow, orange, or pinkish-red, the last two probably being associated with courtship. The bill becomes more orange, and the skin of the lores turns to a dark or purple red in the male. The legs also are said to brighten. The dark head takes on a silvery sheen from the powder down (Lansdown 1988).

Variation: The female Cinnamon Bittern is smaller. It has a sooty crown. Lores are yellow. The back has a generally brown chestnut coloration with a grey wash and large buff spots on wings. The neck has several vertical dark stripes running the length of the neck. The neck plume cluster is smaller than the male's, dark brown edged in buff. The upper wing is cinnamon rufous. The under wing is rufous buff.

Juvenile: The juvenile’s crown is a drab chestnut brown with sandy brown streaking. It has large sandy spots on wings. The throat is white with dark brown stripes going its entire length. Flight feathers are bright chestnut brown contrasting with darker upper wing. Tail is chestnut brown. Under wing chestnut grey.

Chick: The chick has pink chestnut down.

Voice: The throaty “Keuch” call, is the alarm, flight and disturbance call, also rendered “kk, kk, kk, kk” by Lansdown (1988). The “Kwok” call, rendered “kwok, kwok, kwok, kwok” is a territorial, flight, and contact call. “Kok” call, a quiet “kok' or “geg” repeated 10–14 times, is an advertisement call.

Weights and measurements: Length: 40-41 cm. Weight: 106 g.

Field characters

The Cinnamon Bittern is identified by its uniform cinnamon back and upper wings, which lack the contrast of other small herons (Leader 1996b). It is distinguished from the Yellow and Schrenck’s Bitterns by its cinnamon wings and back and less spotting in the female. It is distinguished from pond herons by its cinnamon (not white) wings. It is distinguished from Malayan Night-Heron by its smaller size, thinner bills, olive yellow (not green legs), and lack of large black crown.

Systematics

The Cinnamon Bittern is one of the small bitterns, Ixobrychus, that share similar plumage, white eggs, scutellate tarsi, and ten tail feathers.

Range and status

The Cinnamon Bittern occurs in Pakistan and India, through south east Asia, Indonesia and the Philippines.

Breeding range: It breeds in Pakistan, India (Assam, Kerala, Andaman, Nicobar islands), Nepal (R. Lansdown pers. comm.), Sri Lanka, Bangladesh (R. Lansdown pers. comm.), Maldives, Myanmar (mainland, Andaman), China (south east Sichuan, west Yunnan, Guangdong, Hainan, to Liaoning, Taiwan), Japan (Ryukyu Islands), Thailand (Round1995), Malaysia (peninsular, Saba - Marin and Sheldon 1987), Indonesia (Sumatra - Voous and Marle 1988, Java, Kalimatan, Sulawesi (north), Bali, Lombok, Timor - Noske and Ueda 1996), and Philippines.

Nonbreeding range: Northern populations winter from coastal China and Japan (Ryukyu Islands), south through Indonesia (to Timor).

Migration: Southern Cinnamon Bitterns are sedentary; northern birds are migratory. They move south by September and October. In India, movements may be governed by rainy seasons. Return migration is in April–May. Dispersal records include the Seychelles (Lucking 1995), east Russia (Labzyuk and Glushenko 1984) and an extraordinarily record from Morocco (Robertson 1995).

Status: This is a common to abundant bird through most of its range including, Thailand, Malaysia, Sumatra, Java, Bali, Philippines.

Habitat

This is a rice paddy heron. It occurs especially in rice fields, but also drainage ditches in coconut plantations, reed beds, rank grass and scrub bordering marshes and lakes, grassy areas and coastal mangroves. It occurs along the coast but also up to 1,800 m in the wetlands of the Himalayan foothills. It occurs in grassy and marshy areas near human habitation.

Foraging

The Cinnamon Bittern feeds by Walking Slowly. It also feeds by taking insects by Standing Flycatching, Head Tilting, Peering Over and Head Waving (Lansdown and Rajanathan 1993). It is solitary forager. It is primarily crepuscular (Lansdown 1988) but also feeds at times during the day. On alert it assumes a Bittern Posture. It is not overly shy, and will feed in rice paddies with human workers. It does often choose to roost during the day. Its diet includes insects, mollusks, frogs and fish. Its food is relatively large.

Breeding

In India and south east Asia nesting is July–August, during the monsoon season. It also nests in September–December and February–July in Malay Peninsula, January–March in lowland Sumatra, October–December in upland Sumatra, October–June in Java.

It nests primarily in reed beds and rice fields. It also nests in bamboo, bushes, or flooded trees. Nesting has been found on the ground in southeast China, and at the base of grass tussocks. The nest solitarily, in small loose associations, and near mixed colonies, including Cormorants (Phalacrocorax), Cattle Egrets and Black Bitterns. The nest is small, made of small sticks, sedge, reed or Pandanus leaves, lined with a few dead leaves or fine grass. They are situated low, about 1 m or so above the water.

The male advertises with a Stretch display. The bird positions himself on rice plants, a bush or tree. The bird stands straight, the color the base of the bill flashes bright orange, it crouches low, bill tilted upward, exposing the neck tuft of plumes. The head is lowered and it gives a Kok call. Between active displays, the bird Preens and rubs its head against powder down tracts. It also does Circle Flights with stiff beats and also a display in which he flies up to females with a deep flapping flight and giving Kok or Keuch calls (Lansdown 1988). It also gives the Kwok call when it alights at the end of Circle Flight. It defends its nest site with a Forward display.

Eggs are white. Their size is 33-36.5 x 25.5-26.4 mm. Clutch is 3-4, with a range of 2-5 eggs. Eggs are laid at daily intervals. There is no evidence of double- brooding. Incubation is apparently by both sexes, starts with the first egg. Incubation period is unreported. Young hatch asynchronously and growth is fast. Young can clamber from the nest at 10 days. Nothing is known of fledging periods.

Population dynamics

Nothing is known of the population biology or demography of this species.

Conservation

This is a species that is widespread, locally abundant, and well adapted to human-altered environments. It is hunted in peninsular Malaysia (Lansdown et al. 2000).

Research needs

Understanding the breeding biology of the Cinnamon Bittern is at an early stage. Additional information is needed on the biology, behaviour, and population biology of this species.

Overview

This is not a well-understood heron, despite being relatively easy to observe. It feeds in rice fields and other open herbaceous wetlands by Walking slowly stalking prey, taking invertebrates and relatively large fish. It has a substantial repertoire of behaviours to use in locating and capturing prey and can also make use of a variety of habitats, especially agricultural situations. Much remains to be learned.

Schrenck’s Bittern

Ixobrychus eurhythmus (Swinhoe)

Ardetta eurhythma Swinhoe, 1878. Ibis, p. 74, pl. 2: Amoy and Shanghai.

Other names: Von Schrenck’s Bittern, Little Bittern, Schrenck’s Little Bittern in English; Avetorillo Manchui in Spanish; Blongios de Schrenck in French; Mandschurendommmel in German; O-yoshi-goi in Japanese; Bammangan coklat in Indonesian; Zibei Weiyan in Chinese.

Description

The Schrenck’s Bittern is a small dark heron with a chestnut (or spotted) back and lighter wings, a black stripe down the chest, a black cap, black tail, and in flight bicolored buff and black wings.

Adult: In the adult male, the crown and back of the head are black brown and the sides of the face are chestnut. The bill is relatively short and thick at the base (compared to the other small bitterns). The upper bill is dark horn brown whereas the lower bill is green yellow. The irises are yellow and the lores are olive green to purple pink. The back of the neck, upper back, upper wing scapulars, and rump are bright chestnut brown. Tail is black brown. The upper wing has a pale grey buff patch consisting of the wing coverts contrasting with dark grey flight feathers, paler at tips. The throat and foreneck are buff white, with a distinctive vertical dark rufous centerline. Upper breast is pale red brown. Lower breast and under sides are pale buff, clearly demarked from the darker back. Under wing is silver grey. Legs are dull green brown, yellow at joint and the undersides of the feet are yellow. Bill is black during breeding season.

Variation: Schrenck’s Bittern is sexually dimorphic. The female is smaller, with crown, face, back of neck, back, and upper wing dark chestnut, the back and upper wings with large white to buff spots. On the upper wing, flight feathers are dark brown, and so shows less contrast with the upper wing patch than in male. Tail is black. The throat is cream with black vertical stripes. The under sides are cream broadly streaked in brown. Under wing is silver grey.

Juvenile: The juvenile is dark chestnut spotted buff on back and upper wings. The under sides are broadly streaked in brown and white. Under wing is grey.

Chick: The chick has not been reported.

Voice: The “Squak” call is the flight call. The “Gup” call, rendered “gup, gup, gup” is a breeding call, probably a territorial and advertisement call.

Weights and measurements: Length: 33-36 cm.

Field characters

Schrenck’s Bittern is identified by size, relatively deeper, shorter bill, its chestnut brown upper color demarked from paler under sides, dark throat stripe, black cap, black and buff upper wings, and grey under wings (Leader 1995b). It is distinguished from Yellow Bittern by being slightly larger, having a bill that is deeper at the base and more dagger like, its darker upper parts, less contrast of black and buff on the upper wing, and grey under wing. It is distinguished from the Cinnamon Bittern by being smaller (Payne and Risley 1976 but contrast with Leader 1995b), its chestnut brown (not cinnamon) back, grey under wings, dark (not rufous) flight feathers. Females and immature are distinguished from other small bitterns by the white and buff spots on the back and upper wing.

Systematics

Schrenck’s Bittern is one of the small bitterns, Ixobrychus, which share similar plumage, white eggs, scutellate tarsi, and ten tail feathers. Its range overlaps the Cinnamon Bittern, but they differ in size and color. The species is distinctive among the small bitterns in the spotted color pattern of the female.

Range and status

Schrenck’s Bittern occurs in China, east Russia, and Japan and in winter to Indonesia and Philippines.

Breeding range: This is a northern species, breeding in east Russia (Amurland, Ussuriland, Sakhalin), Korea, east China (Heilungkiang, Guangdong), and north Japan (Honshu northward).

Nonbreeding range: It occurs in non-breeding regularly in the Philippines, and also scattered in south east China (Taiwan, Hainan), Japan (to Ryukyu and Bonin Islands), Vietnam, Indonesia (primarily north Sulawesi (Coates et al. 1997) with few records from Sumatra and west Java (R. Lansdown pers. comm.), Kalimantan (van Balen et al. 1994). There are a few records in summer from Thailand and peninsular Malaysia (R. Lansdown pers. comm.).

Migration: Schrenck’s Bittern is migratory. Southward migration begins in August peaking in October. Return migration is April–May in the south and June in the north of its breeding range. Dispersal records occur from Myanmar in the west to Palau in the east. Extraordinary dispersion records include Europe.

Status: Little is known of the population status of this species (Lansdown et al. 2000). It is uncommon in Russia. In Japan, it is known to breed at only three sites. It is more common in south China. Migrants are recorded regularly as a migrant through south east Asia and Taiwan. There are very few records from wintering areas mostly of individuals, and so it is rare in Philippines and Indonesia.

Habitat

Schrenck’s Bittern occurs in low-lying areas in broad river valleys. It uses open grassy meadows and open marshes along river valleys, reed beds, and also rice fields. It seems to use relatively drier areas such as dry pastures with brush. It has been recorded as occurring in village ponds in east Russia.

Foraging

Nothing is known about the feeding behavior of this species. It hides in the grass or assumes a Bittern Posture when alarmed. It feeds crepuscularly and at times during the day. It is known to eat small fish, shrimp, isopods, dragonfly larvae, and ground crickets. But overall there is a paucity of information on its ecology.

Breeding

The nesting season is in the summer, May–August in Russia, China, and Japan. It nests solitarily in reeds and shrubs over or next to the water. The nest is a small cone, made of dry grass stalks with a lining of dry leaves and grass. It placed within 1 m of the ground, well concealed in tall grass or shrub.

Nothing is known of the courtship behavior of this species. Eggs are white. They measure 32 x 20 mm. The usual clutch is 3-5 eggs: Both parents incubate starting with the first egg. Incubation is 16-18 days. The male is reported to do most of the chick feeding.

Population dynamics

Nothing is known about the population biology or demography of this species.

Conservation

This species is relatively easy to see, frequenting open marshes and rice fields. None the less, it remains uncommon to rare over most of its breeding and wintering areas, with the possible exception of south China. Mostly there is little information available. It is considered to be in the Category Data Deficient by HSG (Hafner et al. 2000). The principal conservation need for this species is for clarification of the breeding distribution and the identification of potentially important areas for their protection. Surveys of known and potential breeding sites should be undertaken and reported, especially in east Russia and east and south China (Hafner et al. 2000).

Research needs

So little is known about the biology of this species that studies of its basic biology are urgently needed. Its status needs to be determined in the breeding range and its distribution in the non-breeding range.

Overview

The ecology of this species is essentially unknown. As one of the small bitterns, some aspects of its biology can be assumed, such as it is likely a marsh-dwelling, Standing predator. But there are few first-hand reports or observations of its biology or behaviour. Contributions can be made to understanding this species by general biological observations.

Yellow Bittern

Ixobrychus sinensis (Gmelin)

Ardea sinensis Gmelin, 1789. Syst. Nat 1(2), p. 642: China.

Other names: Long-nosed Bittern, Chinese Little Bittern, Little Yellow Bittern, Least Bittern in English; Avetorillo Chino in Spanish; Blongios de Chine in French; Chinadommel in German; Yoshi-goi in Japanese; Bakaw-tumana in Philipino (in Philippines); Bambangan kuning in Indonesian; Huang Weiyan in Chinese.

Description

The Yellow Bittern is a small, slender, light buff to light brown heron with a black cap and tail, and long thin bill.

Adult: The Yellow Bittern has a dull black to blue grey crown and crest. The forehead is brown. Its long, thin bill is pale ivory, darker (to black) on the top with a pink tinge, contrasting with yellow green lores and yellow irises. The throat is sandy brown with browner stripes with the sides of the neck buff, often with pink blush. The back is rufous to sandy brown with pink to maroon wash. The wing is characteristically patterned, with a light inner patch and black outer feathers. On the upper wings the major feathers (primaries, secondaries and coverts) are black whereas a patch of wing coverts is light sandy buff. The under wing patch is white, contrasting with the grey of the undersides of the flight feathers. The tail and its coverts are black. The under parts are sandy brown. The legs are yellow green. In courtship the base of the bill flushes red.

Variation: The species is sexually dimorphic in plumage. The females’ crown is indistinctly streaked instead of dark. The hind neck and upper back is rufous. Under parts are streaked dark red brown and buff, with black on sides of breast. The throat has chestnut buff streaks. The wing patch is darker than in males. There is considerable individual and geographic variation in shade of upper parts and under parts.

Juvenile: Immature birds lack the dark crown and have a dark streaked head, back and under sides. Upper bill is dark brown whereas the lower bill is yellow as are the irises. The wings and tail are the distinctive black of the species. Legs are olive yellow.

Chick: The chick is covered by a pinkish down.

Voice: The “Kakak” call, rendered “kakak, kakak”, is the flight call. The “Crrw” call, rendered “crrw, crrw”, is given in the Stretch and also by near fledging juveniles (Lansdown and Rajanathan 1993). The “Ohr” call is a loud, repeated, guttural grunt. A gentler call is given when the bird brings food to the nest. Deep wing flaps are shown in Circle Flights.

Weights and measurements: Length: 38 cm. Weight: 92-104 g.

Field characters

The Yellow Bittern is identified by its tawny brown color, black cap in the adult male, black and tawny wings, and black tail (Leader 1995b). It flies erratically, flashing its black wing edges.

It is distinguished from the Little Bittern by being slightly smaller and having a longer bill, brown (not black) back, and yellow buff (not grey buff to white) wing patch. It is distinguished from Schrenck’s Bittern by being slightly smaller, its lighter upper parts, and more contrast of black and buff (not chestnut and grey) on the upper wing. It is distinguished from immature the Schrenck’s Bittern by lacking white spots on the upper wing. It is distinguished from the Cinnamon Bittern by being slightly smaller and tawny brown (not cinnamon).

Systematics

The Yellow Bittern is one of the small bitterns, Ixobrychus, that share similar plumage, white eggs, scutellate tarsi, and ten tail feathers. It is closely related to the Least and Little bitterns, with which it shares a slender bill, uniform dorsal coloration, and plumage sexual dimorphism. Several subspecies have been proposed on the basis of differences in color, but the variation appears to be within the range of individual variation, which is substantial within the small bitterns.

Range and status

The Yellow Bittern occurs in south east Asia through Indonesia, Philippines, and western Pacific islands.

Breeding range: The Yellow Bittern occurs in Pakistan, India (Mundkur 1985), Nepal, Sri Lanka, north and east Myanmar, south west Thailand, China (south Shanxi, Yunnan, Sichuan, Heilongjiang, Guangxi, Guangdong, Hainan, Taiwan), Russia (Ussuriland, Sakhalin Island, Kurel Islands), Malaysia (peninsular, Sabah) (Lansdown 1987b), Singapore (Lansdown 1986, 1987b), Indonesia (Sumatra, perhaps Kalimantan-Borneo, perhaps Sulawesi) (Smythies 1986, Holmes and Burton 1987, Lansdown 1987b, Coates et al. 1997), Japan, Philippines, New Britain (Bishop 1983), Palau, Micronesia (Yap, Woleai), Guam (United States). Breeding in some parts of this range has been documented only rarely. Disjunct breeding occurs in the Seychelles and in Oman (Erikson and Erikson 1999, Erikson 1999).

Nonbreeding range: During the nonbreeding season it occurs from India, Sri Lanka, south China, Indochina, through Malaysia, Indonesia (Java, Sumatra, Timor, Kai archipelago), New Guinea, and Philippines.

Migration: North and central China populations move south in October. Southern populations are sedentary although there is evidence of local movements in India. Some birds remain in south China, Japan, north Thailand, and Burma, but other northern birds move south to Indonesia. Birds migrate at night. Northward migration is in mid April to late May. Dispersal records include Australia (Queensland, Western Australia), and Christmas Island (Stokes 1990).

Status: Little is known about population sizes. Numbers counted in various places are in the hundreds to low thousands. The species is common to abundant through its range and is undergoing range expansion (Lansdown et al. 2000). It is seriously declining on the Seychelles (J. Gerlach pers. comm.).

Habitat

The Yellow Bittern occurs in fresh water marshes and swamps. It uses reed beds, shrubs or other dense vegetation around paddy fields, lakes, and sluggish rivers, and in mangrove swamps. In the Seychelles, it occurs in freshwater marshes behind the coast. It is primarily a low land species but occurs up to 1,500 m in Sumatra. It may roost in the hundreds in mixed species aggregations (Galbraith et al.1999).

Foraging

The Yellow Bittern feeds by Standing and by Walking Slowly, climbing along reeds but also uses Standing Flycatching and Gleaning to catch small insects. It readily adopts the Bittern Posture when disturbed. It also uses more active foraging techniques such as Wing-flicking, and also Running and Hopping to pursue active prey (Lansdown and Rajanathan 1993).

It tends to be crepuscular, roosting at night and during midday on rice stalks or in gaps left by machinery (Lansdown and Rajanathan 1993). It is less shy than most of the small bitterns and upon landing perches for a moment instead of plunging straight into cover as do other small herons.

Its diet appears to be principally insects, and also fish (such as loaches), frogs, crayfish, freshwater prawns and mollusks (Ueda 1992, Lansdown and Rajanathan 1993). Terrestrial insects are taken in rice fields (Lansdown and Rajanathan 1993). The species is welcomed by rice-growers for eating stem-boring crickets (Smythies 1986).

Breeding

Onset of breeding activity coincides with spring or, in the subtropics, with the rains. It is June–September in India, July–October in Malaysia, May–August in Japan and China (Shiquan1990), and September–April in the Soloman Islands.

They primarily in bushes and herbaceous plants adjacent to extensive rice cultivation systems (Lansdown et al. 2000). Nests are especially placed in bushes surrounding or adjacent to water, for example on levees, next to ditches, around rice fields (Lansdown and Rajanathan 1993), and dwarf mangroves along the coast. They also nest in trees including tall banyan (Ficus). In herbaceous vegetation, nests are placed in reed beds, grass, marsh vegetation over standing water, including cattail (Ma 1990), bulrush, rice, wild sugarcane, bamboo, sword grass. They tend to be less dependent on less dense vegetation than the other small bitterns, but water under the nests sites, probably as protection, appears to be critical point in nest site selection (Uchida and Matsuda 1992).

Nests are solitary, clumped in small dispersed groups, or in small colonies (Lansdown 1987b, Shiquan 1990, Uchida and Matsuda 1992, Ueda 1996). As many as six nests can occur in a single tree (Lansdown and Rathanathan 1993). Nest density in China averaged 11.4 pairs/ha reaching 31.18 pairs/ha in irrigated fields (Shiquan1990). The nest is a pad, 15-25 cm in diameter. It is made of fronds and stalks of marsh vegetation, usually canopied by foliage bent over and woven together. The female builds nests. They typically are low, about 1 m above the water or ground.

The male advertises with a Stretch display, in which it assumes a hunched position, puffs out its throat, gives the Crrw call, and flushes the basal area of the bill (Lansdown and Rajanathan 1993). There does not seem to be an actual stretch, as there is in other small bitterns. The male also performs Circle Flight, with a slow wing flap, flying from, then around, and then back to the advertising site. It frequently Crest Raises, stretches one or other wing, and the jerks the short black tail from side to side at the end of which it depresses the tail to a right angle from the body (Henry 1971). Sites and nests are defended with Snap displays.

The eggs are milky green blue. They are 32-33 x 24.5 mm. Eggs are laid three days after the nest is complete. They are laid at one-day intervals. Clutch size is usually 4-6 with a range of 3-7. Egg laying within a colony may be prolonged, for example June–August in Japan (Uchida and Matsuda 1992). It is believed that two or even three broods may be raised in a season. If so that is a large number of annual nesting attempts for a heron. Moorhens (Gallinula) are reported to dump eggs in Yellow Bitters nests (Ueda 1993). The incubation period is 19 days, range 17-20 (Uchida and Matsuda 1992).

Feeding is by regurgitation, with the chick grasping the parent’s bill. The nestling period is remarkably short (Lu 1987, Uchida and Matsuda 1992). Nestlings can leave the nest as early as 5 to 8 days. Within 15 days, the young begin to clamber out of the nest with the agility characteristic of this species and abandon the nest completely by 20 days.

Population dynamics

Nothing is known of the population biology and dynamics of this species.

Conservation

As a small bittern that is fairly common and not as shy as other species, it is fairly well known, especially by rice farmers, who consider it to be beneficial. Rice fields are a critically important habitat for the species and may be responsible in part for its recent range expansion (Lansdown et al. 2000). It is probably a species that has benefited from the clearing of lowland forests for rice. As a result, its future in many ways depends on the distribution and continuation of rice farming practices conducive to the species. Integrating bittern conservation into rice field management is an important conservation action. Important nesting areas need to be identified so as to emphasize the importance of some rice systems.

Research needs

As a possibly expanding species, its breeding and non-breeding ranges need to be clarified so that future expansion can be documented. Range-wide surveys should be conducted to determine the most important nesting areas, and in each such area the importance of rice cultivation should be evaluated. Individual, sexual, developmental, seasonal, and geographic variability within the species should be further studied to determine if there are populations that merit taxonomic distinctiveness. As an expanding species, additional study of its courtship, foraging, nesting success, and demography are desirable.

Overview

The Yellow Bittern is a bird of fresh water marshes feeding on fish, insects, and other invertebrates. It particularly favours dense water edge vegetation, either reeds or woody plants and rice fields. It feeds in typical small bittern style, Walking and Standing, but also uses surprisingly active behaviours to startle or run down prey. This active behaviour is not as common among egrets. Perhaps the most intriguing aspect of its little known biology is the rapid nesting cycle. Chicks grow exceptionally fast and are quickly independent, and as a result it is possible that the species has multiple clutches during the season. As this is an unusual situation in herons, it suggests an interesting demography. Patterns of survivorship of both young and adults may similarly differ from the heron norm. It is a successful species, one that is in the process of expanding its range, especially in response to rice field development. Its dependence on rice fields becomes a critical aspect of its biology, as it nests more densely in flooded fields. Therefore agricultural practices affect the species.

Little Bittern

Ixobrychus minutus (Linnaeus)

Ardea minuta Linnaeus, 1766, Syst. Nat. ed. 12, p. 240: ‘Helvetia, Aleppo’, restricted type locality, Switzerland.

Subspecies: Ixobrychus minutus podiceps (Bonaparte), 1855: Madagascar; Ixobrychus minutus payesii (Hartlaub), 1858: Casamanse, Senegal; Ixobrychus minutus novaezelandiae (Potts), 1871: Westland, South Island, New Zealand; Ixobrychus minutus dubius Mathews, 1912: Hermann’s Lake, South West Australia.

Other names: Minute Bittern, Leech Bittern, New Zealand Bittern, Australian Bittern, Black-backed Least Bittern in English; Vetorillo Común in Spanish; Blongios nain in French; Zwergdommel in German; Woudaapje in Dutch; Волчок in Russian; Xiao weijan in Chinese.

Description

The Little Bittern is a small heron with a dark back and cap and buff white neck and wing patches.

Adult: The male has a green black crown with elongated feathers forming a modest crest. The bill is yellow or yellow green with dark brown upper edge. Irises are yellow, and the lores are yellow or green. The side of the face is grey washed with a vinaceous tinge. The chin and throat are white with buff center. The back and tail is green black. The flight feathers are green black, which contrast on the upper wing with buff white wing patches. Sides of the upper breast have small tufts of elongated black feathers. The under sides are buff white with minimal brown streaking that is variable among individuals with the under wings white. Legs vary from green, green grey, yellow, green in front and yellow behind. The toes are long.

In breeding the plumage is brighter and upper breast feathers are longer and looser. In courtship the lower bill (of both sexes) flashes red briefly during copulation, nest relief, and other excitement. The lores and orbital skin flush dull red.

Variation: The female is smaller and a duller color. Its crest is black and less glossy than the male. It has a brown or rufous tinge to the dark colors, which also show some streaking. Wing patches are pale brown buff and slightly streaked. The under parts are striped in brown. There are no known differences between sexes in soft part color.

Geographic variation has been recognized in five subspecies. Payesii is smaller with shorter wings than minutus; the neck and wing patches are more red brown to chestnut rather than buff of minutus; the irises become red brown in courtship; legs in breeding are olive green in front and yellow behind.

Podiceps is smaller than minutus or payesii; the adult male has the deep rufous on the neck extending over the whole underparts and under wing and becoming chestnut on the upper parts; the immature bird is darker than minutus.

Dubious has a shorter, thicker bill; the neck and wing are chestnut to rufous; the flight feathers are dull black or dark grey brown contrasting with buff wing patch; the immature has pale primaries with fulvous tips; the female is not well marked.

Novaezelandiae was larger and darker, back and scapulars were dark red brown with rufous lining to the feathers; the hind neck was chestnut; the wing patch are spotted chestnut; the female was more heavily streaked below.

Juvenile: The juvenile bird is more boldly streaked below and above with a red brown tinge. The crown is streaked brown. The wing patches are heavily mottled with brown and buff.

Chick: The downy chick is pink buff above (minutus), reddish buff (payesii), pink buff to brown (dubious) and white below. Irises are black brown. The bill is dull pink turning to grey. The facial skin is blue grey becoming olive yellow. Legs and feet are olive grey with pink toes.

Voice:“Kohr” call is the distinctive and characteristic grunting or barking advertising call used during breeding. It is variously rendered as “kohr, kohr, kohr, kohr”, “hork, hork, hork”, “Cor, orr, orr, orr”, or “gogh, gogh, gogh, gogh” and also “hogh”, “rru” and “woof”. The “Kwer” call is a flight call. It is rendered as “kuk-kuk, kuk-kak”, cuck, cuck,cuck cuck”, Cra, a, a, a, k”, “quer” or “ker-ack”. It is low pitched and abrupt, and sometimes proceeded by a higher pitched “quee”. The “Koh” call is the disturbance call. The “Gek” call is a repeated call given frequently at the nest site, rendered as “gek, gek, gek, gek” or “ek, ek, ek, ek”. A similar “Gak” call is the alarm and threat call. It can be rendered as “kuk”, “gat”, “gack” or “yick”. The “Aark” call is an anxiety call. “Goo” call, rendered “goo, goo”, is used with the Greeting Ceremony. Young beg with “tu, tu, tu, tu, tu”.

Weights and measurements: Length: 25-35 cm. Weight: 140-150 g.

Field characters

The Little Bittern is identified by its small size, dark cap and back, and buff grey wing patches offsetting dark flight feathers. Its flight is rapid for a heron, flying with rapid, shallow, clipped wing beats, legs dangling, often dropping into cover. It is distinguished from the Yellow Bittern by being slightly larger, having a shorter bill, its black (not brown) back, and white to grey buff (not yellow buff) wing patch. It is distinguished from the Cinnamon Bittern by it dark (not cinnamon) back and cap.

Systematics

The Little Bittern is one of the small bitterns, Ixobrychus, that share similar plumage, white eggs, scutellate tarsi, and ten tail feathers. It is closely related to the Least and Yellow bitterns, with which it shares a slender bill, uniform dorsal coloration, and moderate plumage sexual dimorphism. The Little Bittern covers a large discontinuous range, with other small bitterns filling in the range gaps. Novaezelandia is often considered a different species, due to its larger size. Payesii and podiceps are also sometimes considered to be separate species.

Range and status

The Little Bittern occurs in Europe, west Asia, Africa, Madagascar, north India, Australia and New Guinea.

Breeding range: The north boundary of the breeding range of minutus includes England (Allport and Carroll 1989), Netherlands (Bekhuis 1990), Belgium, north Germany, to Estonia, Russia (west Siberia), Azerbaijan, Kazakhstan (Lopatin et al. 1992), Turkmenistan, Uzbekistan, Tajikistan, Kyrgystan, west China (Sinkiang). It breeds in North Africa (Morocco to Tunisia, north Egypt – El Din 1992), Turkey, Israel, Saudi Arabia, Bahrain (possibly breeding), Iraq (possibly breeding), Iran, Pakistan (Sind), India (Kasmir – Holmes and Hatchwell 1991, Uttar Pradesh, Assam), and Nepal.

Payesii occurs in Africa south of the Sahara in Mauritania, Senegal (Morel and Morel 1989), Gambia, Guinea-Bissau, Mali, Sierra Leone, Ghana, Gabon, Principe, Nigeria, south Sudan, south Somalia, Uganda, Rwanda, Kenya, Tanzania (baker and Baker in prep.), south east Congo, Zambia, Malawi, Mozambique, Zimbabwe, Namibia, east and south South Africa (Transvaal, Natal, Cape Province). Podiceps is confined to Madagascar. Novaezelandiae occurred only on South Island New Zealand. Dubius breeds in Australia (Queensland, New South Wales, south Western Australia, north Western Australia – Jaensch 1988).

Nonbreeding range: Minutus from Europe and west Asia move south in winter. A few birds remain in west and south Europe (Mediterranean, Ireland, Britain, Germany, Netherlands, and north Africa) (Cramp and Simmons 1977, Nankinov and Kantarzhiev 1988). Most birds winter in Africa south of the Sahara, mostly in east Africa but also west to Senegal and south to as far as South Africa. Minutus from north India appear to remain there during nonbreeding. Podiceps is probably sedentary; there is some evidence of its moving to Africa in the dry season (Brown et al. 1982) but this is refuted (Baker and Baker in prep.). Dubius also appears to be mostly sedentary but it also occurs in New Guinea, mostly in the southern lowlands (Jaensch 1995, 1996). As far as is known these are wintering birds from Australia, although there remains a possibility of its breeding in New Guinea (Beehler et al. 1986).

Migration: Minutus is migratory across most of its breeding range and has a significant post breeding dispersal. Birds in Europe move south in August–October. They fly singly and in small groups at night. Western birds move through Italy, Spain and France and along the Atlantic coast (Nankinov 1999). They cross the Mediterranean and Sahara in a broad wave. Birds from the east cross Israel, Iraq, Arabia, and Egypt, also in a broad front. Movement in Africa is less clear. Return migration is in March–April. Birds regularly overshoot and land north of the breeding range.

Minutus in the Middle East are partially sedentary. Minutus from north India, payesii and podiceps, are at least partially sedentary, with local movements that are not clearly understood. Payesii shifts in response to rainfall and drought. Podiceps is now understood not to migrate occasionally to Zanzibar as suggested by Brown et al. (1982). Dubius is probably migratory, shifting after wetlands dry out (March–April) from south to north and inland to coast, and also to south Papua-New Guinea. Return migration to the southern breeding areas in Australia is in August–September.

The Little Bittern ranges widely in post breeding dispersal, moving in all directions. Dispersal records include Iceland, Faeroes, Azores, Madeira, and Canary islands and Scandinavia. Dispersal records in the east include Lord Howell Island and New Zealand (O’Donnell and Dilks 1988).

Status: The species is widespread and common in many areas within that range. It has been decreasing in Europe, especially from 1970’s to 1990's, due to habitat loss (Nankinov 1999). Its nesting distribution is now fragmented, and the species appears to be in a rapid decline in west Europe (Marion et al. 2000). Its overall population is 37,000-107,000 pairs, the range reflecting uncertainties in eastern Europe - Romania, Ukraine, and Russia - which together support the greater portion of the European population (Marion et al. 2000).

The Little Bittern is common in north Africa, is increasing in Egypt (El Din 1992) and is more common in Arabia than previously appreciated. It has been under-represented on surveys in Tanzania; a guess at its population there puts it under 10,000 adults (Baker and Baker in prep.). It is rare in South Africa, under 100 pairs. It is uncommon in Madagascar and known from only a few places. It is abundant in parts of India (1,000-2,000 pairs in Kashmir). The population in New Zealand went extinct for unknown reasons – it is one of a few contemporary herons that has suffered extinction (Hilton-Taylor 2000). The Little Bittern is rare and very localized in Australia. It has declined in and west Australia due to habitat loss but may be more common in other areas than is presently appreciated (Jaensch 1989).

Habitat

The habitat used by the species is varied across its huge range. Most typically it uses freshwater wetlands having thick herbaceous vegetation with trees or bushes interspersed nearby. These habitats include peat bogs, reed swamps, edges of lakes, pools, reservoirs, oases, swamps, wooded and marshy edges of streams and rivers, wet grasslands, mangroves, salt marshes, lagoons. In east Africa it prefers smaller, well-vegetated swamps, marshes and drainage ditches (Baker and Baker in prep.) It also can be found in forests. It occurs in lowlands and up to 1,500 m in Madagascar and 1,800 m in the Himalayas.

Typical herbaceous plants used in these habitats include Scirpus, Typha, Phragmites, Baumea, Juncus. Shrubs and trees used include Muehlenbeckia, Melaleuca. It uses human habitats including rice fields, ponds, crop fields, vegetable gardens, and sugar cane fields. Little Bitterns can be very tolerant of humans and nest in places regularly visited by people (Cempulik 1994).

Foraging

The Little Bittern feeds by Walking slowly at the water edge stalking prey from the ground or more characteristically from a perch. It also Walks Quickly using Crouched posture, with head forward, in rapid steps. It Stands at the edge of cover on a perch. It feeds with its head and neck withdrawn. As it sees a prey item, it slowly extends its neck and then stabs. It sometimes it feeds by pecking, jabbing the bill in the water, and using an insect for bait (Baumann 2000).

It is a solitary feeder generally within territories held long term. Its activity periods appear to vary. It is primarily crepuscular over much of its range, but feeds at night and also at times during the day. African birds are primarily diurnal (Langley 1983). When alarmed it assumes the Bittern Posture.

The diet is varied, fish (Perca, Esox, Alburnus, Blicca, Cyprinus, Gambusia, Gobio, Eupomotis, Leuciscus), frogs and tadpoles (Rana), reptiles, eggs and young birds (Olioso 1991), shrimp, crayfish, worms, insects such as crickets (Gryllotalpa), grasshoppers, caterpillars, water bugs, beetles (Notonecta, Naucoris), beetle larvae, dragonflies (Libellula, Aeshna), spiders. Diet differs in various places. In some places it has primarily a fish diet (Langley 1983, Holmes and Hatchwell 1991) and in other places such as Italy insects predominate.

Breeding

The nesting biology of the Little Bittern has been well studied (Langley 1983, Darakchiev et al. 1984, Gerard 1986, Hoyer 1991, Holmes and Hatchwell 1991, Boozic 1992, Lopatin et al. 1992, Cempulik 1994, Martinez Abrain 1994, Gaballero 1997). As expected over such a large range, its nesting season is variable. Nesting occurs in the spring in the north of the range, May–July in Europe and India. It is in the rainy seasons or just after the rainy season in the tropics. Nesting is May–July in north Africa; July–October in west Africa; June–September in Nigeria; May–September in Congo; July, November–December in Uganda; March–April; June in Zambia; April–May in Malawi; February, September, November–December in Zimbabwe; March in Namibia; June–February in South Africa, October–January in Australia.

The species nests in thick herbaceous vegetation, especially near open water pools. But it also in trees or bushes usually over water, and has also been found nesting in trees over dry land. The Little Bittern nests solitarily, but also and perhaps more typically in loose colonies with nests as close as 5 m but usually 30-100 m apart. It likely is extremely residential, in that nests may be reused in consecutive years (Barbier and Boileau 2000).

The nest is a platform with a conical base, 15-20 cm across, and 10 cm thick. In South Africa more substantial nests were 20-35 cm across. The nest is made of stems of herbaceous vegetation, lined with finer material. The nest is typically inserted in reeds, rushes, grass, or papyrus. However in some areas and situations, they nest in trees and bushes and make stick nests. It is built by the male, who starts during the display period.

Early in the breeding season, males establish breeding territories and give the Kohr call, staking out the territory and advertising. When calling, the lower bill flushes red. Territories are defended by an Upright display, Ground and Aerial Supplanting Attacks and a threat display in which the bird places its side to the opponent, spreading wings, lifting one and lowering the other. Males choose a nest site and begin building while continuing to advertise with the Kohr call. The males also use Circle Flights as part of the display. A flight also has been described in which the neck is extended and head held below the body.

Upon formation of the pair bond, birds participate in Contact and Non-contact Bill Clappering, during which the pair cross their necks. The Greeting Ceremony includes the arriving bird approaching the nest, with Bill Clappering, feathers raised, Crest Raising, and gives the Goo call. The bills flush red during the Greeting Ceremony. Upon completion, birds will Bill Clapper. Paired birds will remain together through the nesting season.

Eggs are chalky white. They are laid at intervals of 1 to 3 days. Size averages 36 x 26 mm in Europe, 34.6 x 26.6 mm in South Africa. Clutch size varies geographically, 5-6 in Europe and 3-4 in the tropics and South Africa (Langley 1983). The overall range is 2-7 eggs. Replacement clutches occur if eggs are destroyed but also after young fledge. In some case three broods are raised per year (such as in South Africa). Clutch size decreases later in season (Cempulik 1994).

Incubation, by both parents, begins with the first egg and lasts 16-20 days (Langley 1983, Homes and Hatchwell 1991). Hatching is asynchronous and chicks have their eyes open and legs are fairly developed after hatching. Young are fed in the first 2 days by food deposited on the nest floor. The parents guide the bills of the nestlings to the food. Thereafter, young grasp the parents’ bill and is fed directly. Chicks are brooded through 8-10 days.

Chicks grow relatively fast. By three days they beg by grasping the parent’s bill. Chicks assume the Bittern Posture when disturbed. Pinfeathers develop at 4 days. Sibling rivalry is low, despite asynchronous hatching. And there was not found to be a difference in growth rates relative to hatch order or brood size (Holmes and Hatchwell 1991). Chicks grow quickly and climb out of the nest in one week and can leave the nest entirely by 14-16 days. Maximum growth takes place at 15 days (Langley 1983). The birds fledge flying strongly in 27 days. Success was 56.6% of eggs hatching to nest departure in South Africa and 70-71 in India (Langley 1983, Holmes and Hatchwell 1991).

Population dynamics

Females can nest before their second birthday (Langley 1983). Nothing is known about the demography of this species.

Conservation
The conservation of this species is made difficult by its large range and multiple forms. Given the disjunct distribution of the presently recognized subspecies each with its own situation, conservation should be focused on each population. The European population has been decreasing for some time in some areas but is increasing or even expanding in other areas. It is more widespread in Arabia and the Middle East than previously appreciated (Perennou et al. 2000). The situation in west Europe is clearly critical, however. The population there is continuing to decrease. In Belgium, Netherlands, and France decreases are associated with habitat alteration. However, the general European decrease continues despite this being a species that is tolerant of human alterations and despite the continued availability of apparently suitable habitat. The European population is migratory, and it may be that juvenile or adult mortality in migration and wintering may be a one cause for the widespread decrease. Its populations in east Europe are probably high, but the data are insufficient to detect trends. The Indian population appears to be stable. It is crucial to locate the important nesting areas for this population and undertake protective measures.

The African breeding population is widespread but uncommon in all regions (Turner 2000). Although the two subspecies can be told apart, the existence of widespread wintering by European and west Asian birds makes interpretation of the African breeding population difficult.

The Australian population is considered to be uncommon, but rather appears to be concentrated seasonally in a few highly suitable breeding sites. It has declined and had to shift its distribution due to past hydrological changes in its rivers (Maddock 2000). It is classified as Endangered in Victoria (NRE 2000), where it represents only 0.7% of bird observations in the state since 1970 (Scientific Advisory Committee 1997). Management and conservation of these river systems are critical to the species in Australia. It has been found breeding outside its known range, and evidence of further range expansions should be sought.

The Madagascar population may be down to 100 pairs and is known from a few widely scattered sights. This is a population that is at risk due to habitat alteration and should be considered Vulnerable. The New Zealand population is extinct, having last been seen over 100 years ago. The extinction of this recognized and distinctive subspecies (Hilton-Taylor 2000) suggests the potential precariousness of populations elsewhere. With dispersal arrivals from Australia it is possible that the species will re-establish itself there. The birds in New Guinea are probably migrants from Australia.

Research needs

The causes of the population decrease in west Europe need to be investigated through demographic study of the roles of migration and nonbreeding adult and juvenile mortality. This may require additional banding studies on the breeding ground and also related study in the wintering area. Comparative simultaneous study of east European populations would allow comparisons to be made. Drought, habitat change, loss of staging wetlands in the Sahara and Sahel, and conditions of wintering wetlands could be key environmental factors to be investigated. Surveys should be undertaken of the Madagascar population of the Little Bittern to determine important areas for remaining birds. Surveys should also be undertaken to determine the breeding status in New Guinea. The taxonomy of the species and subspecies of the small bitterns, particularly of the Little/Least/Yellow Bittern group, should be re-examined. At the same time, patterns of geographic variation and the subspecific taxonomy of the several disjunct populations of the Little Bittern should be undertaken, including using molecular techniques.

Overview

The Little Bittern is a bird of dense marsh vegetation, in which it feeds and nests. It forages in the typical bittern manner of Walking and Standing on marsh plants, old nests, or branches. It catches a diversity of prey, but primarily fish or insects, depending on the locality. It is a solitary feeder returning to its territory daily. By maintaining its territory, it has knowledge of its feeding site and avoids competition or disturbance of its prey. It remains paired through the nesting season and typically renests one or more times if the breeding season is long enough. Although young hatch asynchronously, in the situations so far studied, there is no difference in growth or survival of late-hatched young.

Least Bittern

Ixobrychus exilis (Gmelin)

Ardea exilis Gmelin, 1789. Syst. Nat. 1(2), p. 645: Jamaica.

Subspecies: Ixobrychus exilis erythromelas Vieillot, 1817: Paraguay; Ixobrychus exilis bogotensis Chapman, 1914: Suba marshes, Bogota, Colombia; Ixobrychus exilis pullus van Rossem, 1930: Tobari Bay, Sonora, Mexico; Ixobrychus exilis peruvianus Bond, 1955: Vegueta, Lima, Peru.

Other names: Nitlin, Gaulin in English; Avetorillo Panamericano, Garcilla, Garcita, Martinetito, Mirasol Menudo, Gallito, Alcaravancito, Garza Enana, Ardeola in Spanish; Socoí-vermelho in Portuguese; Petit blongios, Blongios minute, Kio jaune, Crabier, Mang lanmé, Martinet in French; Amerikanische Zwergdommel in German.

Description

The Least Bittern is the smallest heron, a pale buff bird with a dark crown and back and buff-colored wing patches.

Adult: The adult male has a green black cap. The irises are bright yellow, sometimes almost orange, and the lores are lime green. The bill is yellow with brown horn along the top ridge. The sides of the face and neck are buff to tawny chestnut, and the hind neck and shoulders are bright buff to chestnut. The chin is white, as are the throat, and underparts, with buff brown throat streaks. Conspicuous tufts of feathers on either side of the upper breast, characteristic of the small bitterns, are black brown with pale edges. The back, rump and tail are glossy green black. The flight feathers are black, whereas the secondary feathers are chestnut, and the upper wing coverts are buff forming a contrasting wing patch. White lines bordering the upper wing are conspicuous above the wing both at rest and in flight. The legs are green in front and yellow behind. The soles of the feet are yellow. The legs and feet are may be suffused with brown or black. In courtship, the Greeting Ceremony and at other times the base of the lower bill flushes red (Kent 1986c).

Variation: The female averages larger than the male. It has chestnut, rather than black, upper parts, a less prominent crown, darker neck stripes, and dark brown chest streaks, and paler wing patch.

The Least Bittern varies geographically and individually (Dickerman 1973b). Compared to exilis described above, erythromelas has the sides of its face and neck rufous; the female has less streaky under parts than typical exilis. Peruvianus is larger, with a long bill, and duller color. Bogotensis has richly colored under-parts; the front of its legs and feet are almost entirely black; the female lacks the rufous tinge to the blackish-brown back found in erythromelas. Pullus is notably dark above, its coverts scarcely contrasting with its flight feathers.

Some variation appears to have both geographic and individual components. A variant once known as “Cory’s Bittern” has the pale areas, especially on the neck, under sides and wing-coverts, replaced by dark chestnut. This form has been reported from Ontario, Florida, and Brazil (Teixeira and Alvarenga 1985).

Juvenile: Immature birds are similar to adult females but have a paler, browner crown and back and dusky streaks on the wing patch. The streaking on their throat and breast is browner than in the female, gives a striped effect

Chick: The young’s head, back and neck are covered with pale buff down, with the longest down on the head forming a crest. The under parts are white. Chicks vary overall from pale to deep buff. The skin of the head, neck and back is pink with abdominal area grey. The bill is pink and black toward the tip, and the irises are white. The legs are pink.

Voice: The Least Bittern is very vocal. The “Coo” call is the low pitched, dove like advertising call of the male. It is rendered “uh, uh, uh, oo, oo, oo, oo, ooah” or “ poo, poo, poo”. The “Tut” call is year round disturbance and alarm call, rendered “tut, tut, tut”, “hah, a, tut, tut, tut”, or “ rick, rick, rick”. The “Gack” call, rendered “gack, gack”, is the contact call, also given from the nest. The “Ank”, call, rendered “ank, ank” or “kuk, kuk”, or “gik, gik” is the disturbance and flight call. “Gra” call, rendered “gra, a, a”, is an aggressive call.

Weights and measurements: Length: 28-36 cm. Weight: 73-95 g.

Field characters

The Least Bittern is identified by its small size, buff and black color scheme with black back and light lines on the side of back, and buff wing patches in flight. It tends to fly rapidly with fast wing beats, but weakly and usually for short distances. When startled into flight, it appears clumsy and flies with its legs dangling and neck extended.

It is distinguished from the immature Green Heron by its smaller size, wing patch, and deep buff to chestnut colors. It is distinguished from the Streaked Bittern by its green black back (not streaked yellow), full black crown (not narrow black crown streak), and dark (not buff) wings.

Systematics

The Least Bittern is one of the small bitterns, Ixobrychus, that share similar plumage, white eggs, scutellate legs scales, and ten tail feathers. It is closely related to the Little and Yellow bitterns, with which it shares a slender bill, uniform dorsal coloration, and moderate plumage sexual dimorphism. The dark color morph was once considered a separate species (Pittaway and Burke 1996). Geographic variation is classified into five subspecies.

Range and status

The Least Bittern has an extensive breeding range in North America, Central America, West Indies, and north, west and east South America.

Breeding range: Exilis breeds from south east Canada (south Quebec, south Ontario, south New Brunswick), east United States (Maine south to Florida and Gulf Coast), central United States and Canada (north Michigan, central Wisconsin, north west Minnesota, north east North Dakota, south Manitoba, south to Texas), west United States (south Oregon, central and south California – Kirk 1995, Wyoming – Grove and Henny 1990, Arizona, New Mexico), Mexico (Baja California, Baja California Sul, Tamaulipas south on the Gulf coast to Tabasco), the north West Indies including Cuba, Jamaica, Bahamas, Cayman Islands, Puerto Rico, Hispaniola, Guadeloupe (Benito Espinal and Portecop 1984), and Central America including Belize, Guatemala, El Salvador, Honduras, Nicaragua, both coasts of Costa Rica (Alvarado 1998), to Panama.

Pullus occurs in northwest Mexico (Sonora and Sinaloa coastlands). Erythromelas occurs in Central and South America in south Panama (south of Chagres River), north Colombia (Cauca, Antioquia, Santa Maria, Boyacá, Cundinamarca), north Venezuela (Guárico, Miranda), Trinidad, Guianas, east Ecuador (Napo), east and south east Brazil (east Amazonas to Gois, Mato Grosso – Cintra and Yamashita 1990, and Santa Catarina), north Bolivia (Beni), Paraguay (Presidente Hayes, Cordillera - Lowen et al. 1997), north east Argentina (Misiones, Corrientes).

Bogotenisis occurs in the savanna east of the Bogotá, Colombia. Peruvianus occurs in west coast Peru (Libertad and Lima province).

Nonbreeding range: Although some birds remain far north, the northern populations in North America winter in the United States Gulf Coast (Louisiana, Texas, Florida), south California, Mexico (Baja California, Baja California Sur), Central America, Greater Antilles, Lesser Antilles (Dominica – Norton 1983) to north South America.

Migration: In the north of its range, the Least Bittern migrates from areas where frost prevails in winter. Southward migration occurs in October. Western birds migrate through western Mexico to about Costa Rica. Eastern birds migrate along the Gulf of Mexico coast and the West Indies, reaching northern Colombia. Return migration is the end of February to early April, or later in the far north. Post breeding dispersal occurs as well. Dispersal records in the north include Newfoundland, northeast Manitoba, British Columbia, Iceland, Azores, Barbados. The southern subspecies appear to be sedentary.

Status: The Least Bittern is widespread in North America, but little is known of its population status because of the difficulty of censusing it. Calling male density ranges from 0.4 to 12 nests/ha (Gibbs et al. 1992a). Although decreasing in some areas and increasing in others, populations in the North America appear stable overall, but information is poor (Morales 2000, Baker et al. 2000). It is common on Cuba, Cayman Islands, Puerto Rico uncommon on the Bahamas, Hispaniola and Guadeloupe, rare on Dominica and Virgin Islands. It is uncommon in Costa Rica (Alvarado pers. comm.) and uncommon to rare in the rest of Central America. It is common in Trinidad and Colombia. As far as is known, populations are stable over most of South America and its known range is being extended by new observations there (Morales 2000). Bogotensis is still common in its restricted range but its wetlands are threatened (Scott and Carbonell 1986). The status of peruvianus is not clear, but it occurs in a small range and uses disturbed areas (Scott and Carbonell 1986).

Habitat

The habitats used by Least Bitterns differ considerably from place to place but usually include very dense vegetation in water, some woody growth, and open water patches. In addition to fresh water marshes, they use lake edge marshes (Rodgers and Schwikert 1999), salt marshes in temperate areas and mangroves in the tropics. It occurs from the coast to 3,100 m in South America.

Foraging

Characteristically, the Least Bittern feeds by Walking Slowly, stalking through the reeds or along the edge of dense reed stands or on branches over the water. It walks in Crouched posture, with its neck extended and its bill nearly touching the water. From this position it launches a rapid strike. It also feeds by Standing in place, and will build feeding platforms to use while Standing. It uses Neck Swaying and catches insects by Gleaning and Standing Flycatching. Among active techniques is Wing Flicking. It tends to change foraging spots after a strike by Walking to a new spot.

The principal prey of Least Bitterns is small fish (Fundulus, Umbra, Lepomis, Perca). Its overall diet also contains crabs, crayfish, leeches, frogs, tadpoles, salamanders, small mammals (shrews, mice), and insects (grasshoppers, dragonflies). It is likely that it eats small birds on occasion.

Breeding

In the north, The Least Bittern nests in the spring and summer, May–August. Nesting in the tropics is more varied and more information is needed. They nest in February–March in Colombia. Nest primarily is in thick herbaceous marshes, with woody vegetation, near open water. The most commonly used habitat is cattail marsh (Typha) (Frederick et al. 1990, Gibbs et al. 1992a). Other herbaceous plants used include Mariscus, Carex, Scirpus, Sagittaria, Phagmites, and mixtures of these. Woody plants include Cephalanthus and mangroves (Rhizophora).

It nests solitarily and in small groups. Nests in groups can be as close as close as 1 m a part resulting in densities of 3-4 nests per 100 square meters (Kushlan 1973b, Rodgers and Schwikert 1999).

The nest is a small platform of herbaceous stalks or sticks. Nests are 15-20 cm wide and 5-12 cm thick placed over the water usually in herbaceous vegetation. A canopy may be made by pulling reed stalks down over the nest. Nest are also placed bushes next to or over the water. The nests are less than 1 m above the water and near open channels or pools within the march (Gibbs et al. 1992a). Primarily the male constructs the nests, and nest construction continues into incubation (Weller 1961).

Male bitterns advertise with the “Coo” call, but little other is known about courtship. After pairing Non-contact and Contact Bill Clappering occur. Greeting Ceremony is used in nest relief. The bird on the nest gives a low “Gra” call. The arriving bird erects its crest and body feathers and both birds Bill Clapper. Territorial defence is well documented. The Bittern Posture seems to be used as a defensive display. They also use a more aggressive Forward display, with head withdrawn and wings spread.

The eggs are white and measure about 31 x 24 mm. Clutches in the northern part of the breeding range tend to be of 4-5 eggs. Mean clutch sizes were 3.8 in South Carolina and 4.08 in Florida (Post 1998, Rogers and Schwikert 1999). In the tropics clutches of 2 or 3 are more usual. The range is 2-7. Incubation begins with the first or second egg and takes 17-20 days. Both sexes incubate and rarely leave the nest unattended.

Hatching is asynchronous occurring over 3-4 days. The young are semialtricial and are fed by regurgitation, the male apparently doing about twice as much of the feeding as the female (Weller 1961). Chicks develop quickly, particularly their legs and feet. They can grasp by day 3, assume the Bittern Posture by day 4, and leave the nest temporarily by day 5. They begin to wander from the nest after six days and leave the nest completely in day 13-15. They return to be fed in the vicinity of the nest. They fledge in 3 1/2 weeks).

Hatching success is 70-84% and the success of a nest to fledge young was 20% to 73% (Gibbs et al. 1992a, Post 1998, Rogers and Schwikert 1999). In Florida, only 47% of the nests produced 2-week-old young (Rodgers and Schwikert 1999). Nesting success in mixed species colonies was greater than for bitterns nesting alone (Post and Seals 1993). Losses are due to flooding, wave action, abandonment, and predation, including mink (Mustela), wrens (Cistothorus), snakes, raccoons (Procyon), crows (Corvus), turtles, and raptors.

Population dynamics

Nothing is known about the population biology or demography of this species.

Conservation

Conservation of this species requires protection and management of its marsh habitat. Water impoundments and wetland construction for various purposes increase the potential habitat for the species as it often nests in cattail marshes created by human activities (Post 1998, Gibbs et al. 1992a, Horstman et al. 1998). In North America, many wetlands are managed by the government for waterfowl and similar purposes, and these provide important opportunities to also provide habitat for bitterns (Gibbs et al. 1992a). Wetland management should take the needs of Least Bitterns into consideration when designing management actions. Standardized monitoring needs to be conducted to evaluate population trends. In Central and South America, information is needed on the breeding distribution and habitat needs of the species.

Research needs

Nothing is known of the courtship and social systems of the species, and these topics need to be studied further. In North American, standardized techniques need to be developed and employed regionally to assess population sizes and trends. Studies are needed of habitat use and the distribution of bitterns during migration and non-breeding to identify major stopover and wintering sites for North American birds. Management techniques need to be developed to create optimal combinations of marsh and open habitat conducive to Least Bittern nesting. In South America, surveys need to be conducted to determine the breeding range of the species through the Amazon and Andes. The status of bitterns in west Peru, and their habitat requirements there, need to be addressed.

Overview

The Least Bittern is a widespread species that characteristically depends on thick emergent marshes. Its small size, thin body, and long toes and nails allow it to move through dense thicket with ease. It feeds quietly by Walking and Standing and often changes locations. Where food is abundant it makes feeding platforms to use within its feeding territories. By feeding from the vegetation it uses and seems to prefer deepwater situations. Its most common habitat is cattail marshes, which tend to increase in disturbed areas. Its diet seems to be mostly fish. This cryplic, inconspicuous small heron can be locally abundant, and much remains to be learned about its sociality.

Streaked Bittern

Ixobrychus involucris (Vieillot)

Ardea involucris Vieillot, 1823. Tabl. Enc. Meth. 3, p. 1127-based on Azara No. 361: Paraguay.

Other names: Stripe-backed Bittern, Azara’s Bittern, Pygmy Bittern, Little Red Heron, Variegated Heron in English; Avetorillo Listado, Garza Enana Amarilla, Mirasol Común in Spanish; Socoi-Amarelo in Portuguese; Blomgios varié in French; Streifendommel in German.

Description

The Streaked Bittern is a small sandy heron with a black crown stripe and heavily black streaked back.

Adult: The Streaked Bittern has a prominent black stripe along the center of its crown from the forehead down the back of the head. The very slender bill is yellow brown. The irises are pale yellow. The hind neck is sandy buff. The back and upper wings are sandy buff heavily streaked with black. Flight feathers are dark buff with tips rufous or cinnamon buff. The throat and under sides are white streaked with buff. The legs and feet green yellow.

Variation: The sexes are alike in plumage. Northern populations are smaller than southern populations.

Juvenile: The juvenile is not described but is presumably similar to the adult.

Chick: Down of the chick is buff above, greyer below.

Voice: The voice has not been documented.

Weights and measurements: Length: 28-33 cm. Weight: 73.4-104.0 g.

Field characters

The Streaked Bittern is identified by its black streaks on a yellow buff background. It is distinguished from the Least Bittern by its streaked yellow buff (not green black) back, light wings, and narrow dark crown (not full dark cap).

Systematics

The Streaked Bittern is one of the small bitterns, Ixobrychus, which share similar plumage, white eggs, scutellate tarsi, and ten tail feathers. It is the only one with streaking on the back. The similarity or distinctiveness of the northern and southern populations is unclear.

Range and status

The Streaked Bittern occurs in northern and southern South America.

Breeding range: The species has a wide but disjunct distributions in South America. It has been thought that the northern and southern populations were separated, but recent records are beginning to fill in distribution gaps within the Amazon basin (Terbough et al. 1984, Olmos 1988). It breeds in Colombia (Atlántico, Magdalena, Meta), north Venezuela (Carabobo, Aragua, Portuguesa), Guyana, Surname, Trinidad), south east Bolivia (Tarija) (Scott and Carbonell 1986), Paraguay, Brazil (Rio Grande do Sul to Minas Gerais - Parrini and Pacheco 1997), Uruguay, north and central Argentina (Rio Negro, Corrientes, – Darrieu and Campari 1997), and central west Chile (Aconcagua, Llanguihue).

Nonbreeding range: The status of the species in the Amazon is not clear. It has now been reported outside breeding range at three sites in northeast Brazil, in Piaui, Maranhão, Sergipe (Olmos and Barbosa 1988). Similarly a range extension to southeast Peru (Madre de Dios - Terbough et al. 1984) covered a few months without evidence of breeding. Determining whether breeding or nonbreeding birds occur in these areas is crucial to understanding the range and status of the species.

Migration: The migratory situation in this species is similarly unresolved. In some places birds occur all year (Chile, Brazil, Argentina) but others it is reported seasonally (Suriname, Argentina, the Amazon) suggesting migration or populations shifts.

Status: There is very little known about the status of this species as no quantitative or trend information is available. It is widespread in South America and probably occurs over a much wider area than is now known. It is reported to be common in some parts of its range, such as Argentina and Colombia, and is likely more common than is appreciated (Morales 2000).

Habitat

The Streaked Bittern usually uses dense marshes and reed beds with tall emergent grasses or sedges. However it now appears that it is not restricted to this habitat in that it also has been recorded in rice fields, along fast mountain streams and in the high Andes surrounded by agriculture and pasture (Scott and Carbonell 1986). In Brazil it was recently encountered and reported on the shore of an artificial lake surrounded by dry land vegetation (Olmos and Barbosa 1988). Although occurring primarily in the low lands a breeding population occurs at 3500 m in the Argentinean Andes (Scott and Carbonell 1986).

Foraging

Like other small bitterns, this species probably feeds by Standing and by Walking. It has been reported to move quickly through the reeds, running up and down with incredible agility. It feeds alone or in pairs at night. When disturbed it quickly adopts the Bittern Posture, freezing and elongating itself and keeping its underside facing the intruder. This bittern is seldom flushed. It flies clumsily before diving back into cover. It eats small fish (Lebestes), crustaceans, insects, including dragonflies, dragonfly larvae and water beetles (Dytiscus).

Breeding

Nesting is reported from July to October in the north (Trinidad) and October–December in the south (Argentina). It nests solitarily in marshes in thick patches of sedge or rush. Nests are small inverted cones or platforms made of stems of herbaceous plants (rushes, etc.). They are attached to the emergent herbaceous plants and placed 30-60 cm above the water.

No observations appear to have been made of courtship rituals. Eggs are yellow, green, and green yellow. Egg size is 32.7 to 33.7 mm x 25.7 to 26.1 mm in Chile and 32 to 33.6 mm x 25.3 to 25.8 mm in Argentina, average of 31 x 24.5 mm in Trinidad. Most of the few clutches found have been 3 eggs. Nothing is known of the incubation, nestling, fledging or post-fledging periods of the reproductive cycle.

Population dynamics

The population biology and demography of this species is unknown.

Conservation

This is a little known species, and the first step in its conservation is to increase basic knowledge of its distribution, breeding locations, and habitat requirements. It is considered Data Deficient by the HSG (Hafner et al. 2000).

Research needs

The Streaked Bittern remains the most enigmatic and least-known representative of the small bitterns. Patterns of geographic variation, if any, among the northern, western and southern populations need to be examined. There is a need to understand its habitat use, especially its use of man-altered habitats. It is necessary to determine if the species is migratory and where it nests or spends non-breeding periods and its biological overlap with the Least Bittern. Determining the range and breeding range of the species in the Amazon is a top priority. The species should be looked for from the Andes slopes to the Atlantic and also in the Orinoco.

Overview

Very little is known about the basic biology of this species. It occurs in extremely dense vegetation where observations are difficult. Consequently, we know only that it feeds within dense reed beds or marshes probably on fish and insects. Recent information showing its use of atypical and human-altered habitat broadens the perspective on its habitat use. Similarly, recent information on its occurrence over a much larger range, may lead to revising our understanding of its distribution, movements, and annual cycle. Much more needs to be understood about this species.

Australasian Bittern

Botaurus poiciloptilus (Wagler)

Ardea poiciloptila Wagler, 1827. Syst. Av., Ardea, sp. 28: New South Wales.

Other names: Australian Bittern, Boomer, Brown Bittern, Bull-bird in English; Avetoro Australiano in Spanish; Butor d'Australie in French; Australische rohrdommel in German.

Description

The Australasian Bittern is a stocky, thick necked, medium sized, mottled dark brown and buff heron with a black mustache.

Adult: The Australasian Bittern’s crown is brown. The upper bill is yellow to buff with the top of the bill dark brown to grey black, somewhat short relative to the New World large bitterns. The loral area is variable, green grey to blue grey, extending onto the lower bill. The irises are yellow. A narrow stripe of skin from the nostrils to the bill is dark olive brown. A light line above the eye is buff white. Side of the face is buff. A dark mustachio streak runs from the gape to the sides of the neck. It is dark brown near the bill becoming paler brown as it blends into the neck. The hind neck and back are dark brown with buff streaks and freckling giving a general mottled and streaked appearance. Upper wings are finely barred in buff and brown with dark brown flight feathers irregularly barred or spotted with buff. The tail is brown with buff fringes. Chin and upper throat is white with mottled brown central stripe. Lower throat and foreneck are buff white with dark brown longitudinal stripes and freckling. Belly and feathered thighs are white. Under wing is buff white with freckled brown. The legs and feet are green yellow to dark olive. There is no information on changes during courtship or breeding but it is likely that reported blue green lores and orange brown irises are breeding colors.

Variation: Females are much smaller than males but have the same plumage. However, individual plumage is highly variable. Dark, light, in-between, and red birds occur. Darker birds have a darker mustachio stripe. The upper parts are dark brown with little of the pale streaking or freckling. The dark feathers make the bird appear uniformly dark to black at a distance. Birds are also reported that are reddish, with a cinnamon buff side of face and rufous upper parts and upper wing.

Juvenile: Immature birds are similar to adults but are paler, with a yellow tinge to the basic color, and underparts streaked rufous. Iris is yellow. Bill is yellow green to olive grey with grey brown top of bill. Facial skin is light green to green yellow, with the narrow stripe between the eye and bill being black green. The legs are dark olive.

Chick: The hatchling has long sparse dark brown down. As they are older, they become buff to yellow brown above and yellow brown below with a white chin and throat.

Voice: The “Boom” call is the loud, resonant call given during the breeding season by territorial males. They start with four short quiet gasps followed by “woomph, gasp, woom”. Each call typically includes 2-3 booms. Males call back and forth to each other. The “Craak” call is a short harsh alarm call and also the flight call when disturbed. A bubbling sound is reported from a female returning to the nest. This and other vocalizations need more study.

Weights and measurements: Length: 66-76 cm. Weight: females 571-1,135 g, males 875-2,085 g.

Field characters

The Australasian Bittern is identified by its stocky build, thick neck, medium size, brown and buff mottled plumage, plain brown crown, dark brown moustache, broadly brown streaked neck and breast, and finely vermiculated and spotted upper sides. When disturbed it flies up heavily on broad bowed wings with legs dangling, and quickly plunges back down into the vegetation without circling. In full flight, this bittern flies with steady slow wing-beats, reported to be rather owl-like (Marchant and Higgins 1990).

It is distinguished from the immature Rufescens Night-Heron by being larger with a heavier, stockier build and less hunched appearance, having mottled (not densely spotted) back and upper wings. It also is not usually found in flocks nor perched in trees. Its bill is relatively shorter (shorter than length of head vs slightly longer in the night heron) (Marchant and Higgins 1990). It is distinguished from the Black Bittern by being larger, stockier, brown (not black) and upper parts. It is distinguished from the Eurasian Bittern by having darker upper parts, much darker in some, especially on the neck and back, which also are less strongly marked in paler shades.

Systematics

The Australasian Bittern is one of the four large Botaurus bitterns, which all have streaked brown plumage, scutellate tarsi, 10 tail feathers, and a booming call. It is most closely related to the Eurasian Bittern (Payne and Risely 1976, Sibley and Monroe 1990). The birds of south west Australia and New Zealand in the past have been recognized as separate subspecies.

Range and status

The Australasian Bittern occurs in Australia, New Zealand and nearby islands.

Breeding range: The Australasian Bittern occurs in south east Australia (south Queensland, New South Wales, Victoria, east South Australia), west Australia (south Western Australia), Bass strait Islands, Tasmania, New Zealand (North Island, South Island, Stewart Island, Great Barrier Island, Mayor Island), New Caledonia and Loyalty Islands. There in fact are few records of actual breeding within this range, but it is assumed due to year-round residency.

Migration: The species is generally sedentary. It likely undertakes seasonal population shifts associated with the wet and dry season, with some suggestion of winter influxes occurring along the coasts of Australia and New Zealand (Whiteside 1989, Marchant and Higgins 1990). There also appears to be movement in exceptional dry or wet situations. Dispersal occasionally occurs, perhaps more so in the past when populations were higher in New Zealand. Dispersal birds occur in Western Australia, and on islands including Chatham Island (more frequently in the past), Kapiti Island, Great Mercury Island, and Lord Howe Island, and recently in the Torres Strait (Stokes 1983), suggesting that the species should be looked for in New Guinea.

Status: It is widespread New South Wales, Victoria and South Australia, being most common in the Murray-Darling basin and coastal areas. In Tasmania, it is most common in east. Populations in Western Australia have decreased in the last century to about 100 pairs, and it is now confined to high rainfall areas along the west coastal plain. It is widespread but thought to be declining in New Zealand. The population there is 580-725 birds. It was once common on the largest of the Loyalty Islands, but its current status is unclear and is likely extirpated. It is not clear if the Chatham Island population was resident or dispersive, but it has not been reported there since 1910.

New Zealand distribution maps for the species (Marchant and Higgins 1990, Heather and Robertson 1996) show it as occurring throughout the whole of the North and South Islands, which can be somewhat misleading (M. Maddock pers. comm.). There are mountains in the North Island and along the whole spine of the South Island that are up to more than 2,000 m in altitude, capped with permanent snow and glaciers and heavily forested on the slopes below the snow line. However, deep valleys with lakeshore wetlands suitable for the bitterns within the habitable altitude range for the species penetrate well into the mountains. For example Chambers (1989) recommends Lakes Manapouri and Te Anau, surrounded by ranges of 1,000 m or more in altitude, at the eastern margin of Fiordland, as suitable locations for observing the bird.

Habitat

The Australasian Bittern typically uses permanent fresh water marshes with dense reed and rush beds situated in shallow (less than 30 cm) water. They occur along rivers, pools, lakes and swamps. They particularly use places near the edges of pools and waterways through the marsh. Typical vegetation includes Typha, Phragmites, Juncus, Baumea, Eleocharis, Gahnia, Bulboschoenus, Ludwigia, Eragrostis and small bushes. It usually feeds and nests within the marsh, near the interface of the marsh and open water. It sometimes does occur in more open situations, on mud banks and in open water. It also uses, temporary pools, tidal marsh near the mouths of freshwater creeks and seeps, mangroves (Miller and Miller 1991), rice fields, tall wet pasture, and drainage ditches (Grant and Bennett 1986). It is primarily a bird of low land swamps but occurs to 300 m in New Zealand.

Foraging

The Australian Bittern is generally a solitary hunter, although it also feeds in pairs and sometimes in loose groups of up to 12 birds. It feeds primarily at night, but is also observed to feed crepuscularly and by day especially in winter. More information is needed on the daily cycle.

It feeds by Standing motionless, waiting for prey. It feeds from the edge of thick vegetation, from the bank, or from overhanging branches. It establishes feeding spots by flattening areas in the reeds, which often are littered with discarded remains of crustaceans and frogs. It also Walks slowly in a Crouched almost horizontal posture, moving forward with great deliberation, often knee-deep in water or along a bank. Each foot in turn is lifted high as it progresses. It frequently Neck Sways. It also has been recorded as Baiting using pieces of grass to lure fish.

On locating prey it makes a rapid Bill Strike by pivoting forward on its legs with neck and back straight (Whiteside 1989). The upper legs are short relative to the lower legs providing the pivot. They also Lunge from a crouched position, leaving the ground. The rapidly assume a Bittern Posture when encountering an intrusion but also uses it for surveillance (Whiteside 1989). When disturbed they fly up and return into the marsh quickly.

The diet is variable, but fundamentally fish (eels, trout, Crassius), frogs (Hyla), and crayfish (Cherax). The overall diet includes insects (cutworms, weevils, crickets, grasshoppers), spiders, mollusks, lizards, rats, mice, and small birds, including white-eye (Zosterops). In New Zealand the introduced Hyla appears to constitute its main prey. But in all areas, the diet has not been studied in any detail.

Breeding

Breeding is October–February, but more information is needed. It nests in reed beds up to 2.5 m tall, usually near openings such as pools or streams. It uses small to large wetlands, 5-300 ha, reportedly usually only one bird per wetland. Four and five birds were reported in 200 ha swamps, or 2/100 ha (Marchant and Higgins 1990).

The bittern is a solitary nester. However several (up to 7) nests can be found in close proximity in the same reed bed. These are assumed to belong to one male and may represent polygamous breeding. More details are needed. The nest is a platform 30-40 cm across, 20-22 cm thick. It is made of reed and occasionally grass placed within the marsh vegetation seldom more than 10-30 cm above normal water level. Females appear to build the nest alone.

The male announces and advertises its territory in the spring with its Boom Call. This far carrying call is given mostly at dawn and dusk. Circle Flights have been recorded with feet dangling. A flight display has also been described involving two birds flying alternating slow flapping and gliding. It is likely the Bittern Posture is used as a display, in which the brown mustachial streak is expanded into a ruff on either side of the head and neck.

The eggs are brown olive or green cream, average 52 x 38 mm. The clutch is 4-5; range is 3-6 eggs. Incubation starts with the first egg and is 25 days. The female alone incubates.

Renesting occurs when eggs are lost. The chicks are fed by regurgitation into the nest, apparently by the female. The chicks can leave the nest in 2-3 weeks, and begin to wander into the surrounding reeds. They fledge in about 7 weeks. Nothing is known of the nesting success of the species.

Population dynamics

Nothing is known of the population biology or demographics of the species.

Conservation

Information on status is slim because of its occurrence in dense, inaccessible habitats. Although locally common in the Murray-Darling river system, long-term population declines elsewhere in Australia and New Zealand are matters of grave concern. In Australia, declines are caused by habitat alteration-drainage, salinization, damming, grazing, clearing for agriculture, and peat extraction. In New Zealand, swamp drainage and, previously, hunting for feathers sought-after by trout fishermen caused the decline. That these two presumably isolated, declining populations have been thought distinctive enough to merit subspecific status suggests the importance of focusing conservation measures on these disjunct areas. In many ways, however, the viability of the species as a whole depends on the health of the Murray-Darling system. In west Australia and New Zealand habitat restoration may be required. Like other large bitterns, this species favors Typha marshes, and could use disturbed wetlands. Properly managed disturbed and artificial wetlands can be an integral part of a conservation strategy. In addition to protecting habitat in parks and reserves, the importance of habitat management on private land cannot be overstated (Corrick 1995). Conservation of this species needs to become a higher priority (Hafner et al. 2000). It is categorized as Critically Endangered by HSG. It is considered to be Vulnerable by IUCN (IUCN 2003). It also is a Vulnerable species in Schedule 2 (updated 1999) under the NSW Scientific Committee Threatened Species Conservation Act 1995 and in Victoria, its conservation status is classified as Endangered (NRE 2000). One reason why its conservation status is inconsistent is that its actual status is surprisingly poorly known. Although its estimated world population is well under 10,000 birds (Hafner et al. 2000), it may be far smaller in that fewer than 100 pairs were surveyed in west Australia, and fewer than 800 birds estimated in New Zealand. The nesting population in southeast Australia has not been documented. Actions required include a complete survey of the breeding population in east Australia, especially in the Murray-Darling system, and New Zealand, identification of important areas (those that support 100 or more birds), development of habitat management recommendations including enhancing the use of artificial and disturbed wetlands, implementation of a range-wise strategy for habitat protection and management, and establishing a monitoring programme. Conservation should focus independently on west Australia, east Australia, and New Zealand.

Research needs

So little is known about the biology, breeding range and dispersion, behaviour, and habitat requirements of this species, that comprehensive studies of its biology are needed. Actual records of nesting are few. Surveys should be undertaken to determine the actual breeding range and dispersion of nesting across the range. Especially important are the areas where declines are occurring and also the MurrayDarling basin, which supports the majority of the population. The species’ use of Typha marshes should be carefully studied in order to determine required habitat characteristics within this marsh type. Such information can be used to develope habitat management recommendations for enhancing the bird’s use of artificial and disturbed Typha marshes. The species is highly variable in plumage characteristics. It is unclear what part of this variation is individual and what has geographic components. Intra-specific variation in plumage and morphometrics should be studied to re-examine the distinctiveness of west Australia and New Zealand populations. The results may have important conservation implications.

Overview

This is a reed-bed species. It characteristically uses patches of emergent marshes of grass, reed, or sedge, located in swamps, along rivers, or as isolated wetlands. Its habits and morphology are designed to make maximal use of concealment within the thick marsh vegetation. Its long toes allow it to support itself on the grass; its short legs, particularly the upper legs, allow it to crouch low to the water while Standing or Walking and still be able to lunge forward to strike. It eats fish, frogs, and insects, but overall has a broad diet of whatever it can encounter in the marsh. It has the potential for being adaptable in that its favoured habitat is also one that responds well to human hydrological alteration and it is able to use more open and even human-created habitats. It none the less occurs primarily in inaccessible situations, and its biology remains very much unknown.

Eurasian Bittern

Botaurus stellaris (Linnaeus)

Ardea stellaris Linnaeus, 1758. Syst. Nat. ed. 10, p.114: Europe; restricted type locality, Sweden.

Subspecies: Botaurus stellaris capensis (Schlegel), 1863: South Africa.

Other names: The Bittern, Great Bittern, Common Bittern, European Bittern, African Bittern, Boomer in English; Avetoro Común in Spanish; Butor étoilé in French; Rohrdommel in German; Boerdomp in Dutch; Built in Russian; Rördrom in Swedish; Sankano-goi in Japanese; Da mayan in Chinese.

Description

The Eurasian Bittern is a stocky, thick necked, medium sized, mottled, black crowned, golden brown heron.

Adult: The Eurasian Bittern is the largest of the large bitterns. It has a black cap. The long bill is yellow with the top being brown and becoming almost black at the tip. The iris is yellow and a line above the eye is pale buff. The loral area is green, extending on to the lower bill. The sides of the head are uniform buff brown. The neck is buff brown narrowly barred brown. The chin and throat are cream white with rufous brown median streak. A weak black to dark brown moustache extends from the bill gape onto the neck. The hind neck and back are golden-brown, consisting of black and buff mottling and barring. Two “shoulder plumes” consist of elongated feathers with a brown centre and large white border, usually concealed by the folded wings. The upper wings are pale rufous buff, darker on the leading edge, and blotched with black. The flight feathers are pale red brown to black, with black spots. The foreneck and breast are yellow buff with longitudinal brown streaks and finely spotted black. The streaks are widest on the chest and narrowing on belly. The feathers of the foreneck are thick and elongated into a bib. The belly is yellow buff. The under wing is pale buff with grey mottling. Leg and feet are pale green. The soles of the feet and back of lower legs are yellow. In breeding the loral area is light blue in the male and light brown in the female. It is likely that reports of orange red irises are indicative of a color change in courtship (Wood 1986).

Variation: Males are significantly larger than females. The females may tend to be less well marked than the males. There is much individual variation in the dark plumage markings, some individuals appearing quite pale. There also is geographical variation. Birds from east Asia tend to be more boldly barred, and were formerly considered a subspecies. The disjunct birds of southern Africa, capensis, are slightly smaller and darker, with more narrow and irregular barring on the flight feathers than stellaris.

Juvenile: Juveniles are very similar to adults. They are paler with browner stripes, have a browner crown and less distinct brown, not black, moustache streak.

Chick: The chick has cinnamon tawny to rufous brown down on the upper parts. Chin and throat are white. The under parts are rufous buff. Bill and leg are blue green.

Voice: The “Boom” call consists of two to four deep, resonant booms repeated at 1-2 sec intervals, preceded by a few short grunts or pumps and sometimes accompanied by Bill Clappering. The sequence of pumps and booms in the Boom Call is variable among individuals and often among the calls of an individual (McGregor and Byle 1992, Gilbert et al. 1994, Puglisi et al. 1997). The call has been rendered as “up, up, up, rumb”, “umb, uh, uh, uh, ub”, “up, up, up, rumb”, and “hu, hu, umb, ub”. The Boom Call is used during the breeding season for advertisement and territorial defense (Puglisi et al. 1997) and is audible for up to 5 km. The female in answering the Boom Call uses the “Wumph” call.

The “Kau” call is a flight call, contact call and disturbance call; perhaps the multiple use of a call is not unexpected for a bird from dense habitat. It has been rendered as “kau” “aargh” “aark, aark” and “awk, awk”. The “Kro” call is a disturbance or warning call, rendered as a rapid, short “ko, ko, ko”, and “kro, kro, kro”. The “Kra” call is a threat or warning call. Young beg with a crackling “rah, rah, rah.”

Weights and measurements: Length: 70-80 cm. Weight: females 867-1,150 g; males 966-1,940 g.

Field characters

The Eurasian Bittern is identified by its stocky build, thick neck, medium size, golden brown mottled plumage, black crown and dark moustache. If disturbed it flies up with neck extended and legs dangling, and quickly drops back into the reeds. In long flight it has steady slow wing-beats, on broad rounded wings. Described as owl-like, it flies low over the marsh, with head retracted and legs trailing.

It is distinguished from the immature Black Crowned Night-Heron by being larger with a heavier, stockier build and less hunched appearance, having back and upper wings mottled with black (not densely spotted white), black crown, and moustache. It does not flock or perch in trees. It is distinguished from the North American Bittern by being larger, with a black (not rusty brown) cap, indistinct black (rather than prominent large) moustache stripe on the head, more boldly marked plumage, broader wings without dark flight feathers (Lansdown 2000).

Systematics

The Eurasian Bittern is one of the four large Botaurus bitterns, which all have streaked brown plumage, scutellate tarsi, 10 tail feathers, and a booming call. It is most closely related to the Australasian Bittern (Payne and Risely 1976, Sibley and Monroe 1990).

Range and status

The Eurasian Bittern is a bird of the Old World temperate and tropical zones of Europe, Asia and Africa.

Breeding range: It breeds from England, Wales, Sweden, Finland, Germany, Lithuania (Matiukas 1990), Italy, Belarus, European Russia), south through Europe, north Africa (north Morocco, Algeria) Albania, Bulgaria, Turkey (Kasparek 1986), north Iran, Kazakstan, Azerbaijan, Turkmenistan, Uzbekistan, Tajikistan, Kirghizstan, Afghanistan, Mongolia, north China (Sinkiang to Heilongjiang), Russia (Siberia to 64° N, Yakutia, Amurland, Ussuriland, Sakhalin Island), North Korea, South Korea, Japan (Hokkaido). Capensis is presently known to nest only in Natal and Transvaal in South Africa and probably Zambia.

Nonbreeding range: Stellaris winters from central Europe, east Europe to Ukraine,

east Saudi Arabia, Iraq, Iran, Turkmenistan, Pakistan, north India, Nepal, Bangladesh, south east China (including Hong Kong – Leader 1999), Korea, Japan (Honshu), Myanmar, Cambodia, Vietnam, south Thailand, north Malaysia (peninsular), also north Africa in Libya, Egypt, sub-Saharan Africa in Mauritania, Senegal, Ghana, Gambia, Gabon, Nigeria, Cameroon (Robertson 1993), Kenya, north Zaire, Sudan, Ethiopia, Eritrea.

The known breeding sites for capensis are few. However it occurs over much wide range in central and south Africa. Until proven otherwise, this is considered a nonbreeding range. They occur in central Angola, Namibia (Hines 1985-7), north Zambia, Zimbabwe, south Tanzania, Malawi (Johnston Stewart 1989), central Mozambique, northwest Botswana, north Seychelles, South Africa (Vernon 1993).

Migration: The north Eurasian populations are partially migratory. Some birds remain in breeding areas where water does not freeze, or stay further north in mild winters (Bibby 1981, Andersen 1989, Nankinov 1991, Kolland 1996, Mundt 1996, Gauggel 1999, Bernasconi et al. 1999). Some populations, such as England and Netherlands, are nearly residential.

Both Fall and Spring migration are primarily at night (Puglisi and Baldaccini 2000). Birds move singly or in small flocks. Southward migration is variable, seriously getting underway after the first hard frost, generally September to as late as December. West European birds move south through France and Spain; others move through Greece and Italy (Voisin 1991). They cross the Sahara where they occur in oases. Return migration is February–April. The origin of birds wintering in Iran and Iraq is not known, probably Russia (Voisin 1991). Asian populations move south to the northern half of the Indian subcontinent, Myanmar and throughout central China to the Chinese coast. Migration here is little understood (Leader 1999).

The African race capensis is mainly sedentary. Some movements take place, mainly to the southwest, and these are governed principally by rainfall.

Post breeding dispersal is extensive, especially of immature birds. Dispersal records include Iceland, Faeroes, Madeira, Azores, Canary Islands, Norway (Jebekk 1996), Syria, Jordan, north Russia (Pleshak 1999), south India, Myanmar, Sri Lanka (Gunawardene and Wijesinghe 1986), Ryukyu Islands, Taiwan, Malaysia (peninsular), Philippines (Luzon), Brunei (Mann 1987).

Status: Formerly widespread and abundant, the Eurasian Bittern has suffered a steady decline in numbers in Europe, since the 19^th century, notably from 1970-1990 For example, it was extirpated from England in 1868. It began a comeback through Europe in early 1900's, returning to England in 1911. It increased population and range into the 1960’s and then began a second decline. At present, the bittern remains widespread in Europe, but with relatively few remaining in the west. Declines in some areas have been rapid and alarming, such as Spain but is reversed at other sites (Duhautois 1984, Smith and Tyler 1993, Puglisi et al. 1995a, Vicens 1997, Kayser et al. 1998, Marion et al. 2000).

The total European population is 20,000-44,000 pairs (Marion et al. 2000). Russia supports 63% of the European population, 10,000-30,000 pairs, but its status there is little known. Ukraine, Poland, Belarus, and Romania account for 24% of the European population. It is locally abundant in Turkey (Kazilirmak Delta) and Romania (Danube Delta) (Hafner 2000). In North Africa, it is very rare, occurring only in a few pockets of fresh water. In Africa records of capensis are sparse and has clearly has undergone a considerable decline, especially in recent years. It is known to breed in South Africa and is rare in Zambia. It is common in Iran but considered to be uncommon through its breeding and nonbreeding range in Asia.

Habitat

The Eurasian Bittern is a bird of densely vegetated wetlands with extensive beds of tall grass or sedge. Usually these marshes are characterized by being shallow, fresh or brackish, with stable water level, low acidity, low elevation (less than 200 m, and reed stands of varying ages interspersed with open water. Marshes dominated by cane, Phragmites are favoured in Europe. It also uses Scirpus marshes, papyrus swamp, brackish marshes, and coastal dune wetlands. Rice fields may be serving as a potentially important habitat (Alessandria et al. 1992). Outside the nesting season, its requirements are less restrictive. Beyond the reed bed, it uses more varied and open aquatic habitats such as small ponds, gravel pits, wet grassy meadows, ditches, fish ponds, water cress beds, other floating leafed plant beds, and sewage lagoons (le Mair et al. 1995). During winter, it tends to come out of the reeds to find open or running water in which to feed. In very cold weather the species may occur nearly anywhere there is open water.

Foraging

The Eurasian Bittern is a solitary feeder. It fiercely defends its feeding and nesting area during breeding, but may occur in larger loose groups outside of nesting. It is mainly crepuscular, it also hunts during the day and at night, within and at the edges or reed beds. The main method of hunting is Walking slowly, with great stealth. It walks in an extreme Crouched posture, the bill pointed forward, the feet lifted high with each step. It also feeds by Standing, often as an intermission in Walking. It also Walks Quickly, especially across open spaces and also Swims across open water between patches of cover (Lindblad 1995). It has been observed to Run across open habitat picking up prey items. It Foot Stirs to inspire fish into movement.

The bittern tends to feed at the edge between emergent reeds and open water, such as a pool, channel, or ditch. They tend to avoid unflooded ground and walks by climbing over the emergent stems, grasping them with long toes. They also climb up the stems for observations, and to sunbathe. They avoid shrub, which has consequences when marsh succession occurs.

Large areas are covered in the search for food. It captures prey by stabbing using its entire body. Fish are shaken, beaten and stabbed before consumption. It often uses the concealing Bittern Posture, in response to disturbance but also for surveillance as it can peer directly forward when its bill is raised; it has been observed to hold this posture for hours. The bittern generally is found on the ground or in herbaceous growth, but on occasion uses trees (Lunn 1992).

A wide variety of foods is taken, varying with locality and season. Fish, amphibians and insects usually dominate the diet. Fish taken are diverse depending on availability. Species include Esox, Eupomotis, Cyprinus, Salmo, Perca, Thymallus, Tinca, Anguilla, Cottus, Leuciscus, and Rutilus. The diet also includes frogs, tadpoles and salamanders (Rana, Triton, Bombina, Leuciscus), worms (Lumbricus), crustaceans, insects (water beetles, water bugs, grasshoppers, dragonflies, leaf miners), small mammals (Avicola, Mus), birds (Anas) (Loison 1991), snakes (Natrix). In some areas eels, frogs or tadpoles dominate the diet. The diet is particularly challenging for birds that remain north in the nonbreeding season, where they use atypical habitat and prey (Windisch 1999)

Breeding

The Eurasian Bittern nests in March–July in Europe, sometimes earlier; September–January in South Africa. Generally nesting is in the rains in the tropics, but there is little information. During the breeding season, the bittern is nearly restricted to dense reed beds. The ideal habitat is restrictive: dense plants, of both old and young stems, stably flooded, shallow, with clearings or channels. They may use either fresh or brackish water, but not saline. In addition to Phragmites, plants used include Scirpus, rice, Papyrus, Bolboschoenus, Cladium, Juncus.

Breeding is essentially solitary. Density varies from 2/100 ha to 100/100 ha, depending on the habitat quality. However under suitable habitat conditions, nests may be rather close together, as many as 10 were counted in 0.5 ha (200/100 ha). This is highly unusual, but nests are also close in situations where there are more than a single female associated with a male. The nest is a pad of matted reeds and other marsh vegetation, lined with finer material. It appears carelessly put together and flattened by use. Nests are 30-40 cm wide and 10-15 cm high, placed on and within the reeds at water level. It is built by the female alone. The bittern’s movements soon create radiating tracks through the nearby marsh. Material is added through the nesting period.

In Spring, the male claims its territory and advertises by giving is Boom Call (Fontanelli et al. 1995). Nonmigrating birds begin to call in late winter. The male will occupy and defend its territory through July. The Boom Call is produced with the bill closed and pointing downwards and neck feathers fluffed out. The Boom Call is most given at dawn and dusk, but also throughout all hours of the day and night (Puglisi et al. 1997).

Males defend their home range territories (Puglisi et al. 1999). They are extremely aggressive in its defence. Supplanting Flights occur, as does Aerial Fighting, which may end in the death of one of the bitterns. Forward displays are used to defend sites. The bird has its legs bent, neck bent back, bill open, wings bent forward, crest, neck feathers, scapulars, and shoulder tufts erected (Gorman 1995). Attacks are made by a strong beak jab, perhaps jumping forward. Chest pecking may be a ritualized outcome of low intensity attacks. Subservient birds respond with a Withdrawn Crouch. However, bitterns sometimes kill other bitterns. The bittern also defends against other species, particularly the Marsh Harrier (Circus) and Carrion Crows (Corvus), and is known to loose prey to pirating birds, such as Grey Herons (Kington 1991). Interactions between pairing individuals are seldom described. In close proximity, the shoulder plumes are displayed (Grull et al. 1988).

In addition to the Boom Call, displays include individuals or several birds indulging in extensive Circle Flights over the reed beds. The flying is erratic, at heights of up to 60 m and for as long as ten minutes, ranging over large areas of the habitat. When flying together the bitterns circle around each other or shoot upwards and downwards again.

This is the heron species in which true polygamous mating has been best shown. It is not unusual, and the male may have up to five mates. The eggs are olive brown, occasionally with some fine spotting at the large end. They average 53 x 39 mm. The normal clutch is 4-5 eggs; range is 3-7. Eggs are laid at 2-3 day intervals. The species has long been known to be single brooded, however double brooding has recently been documented (Mallord et al. 2000). Only the female incubates. Incubation begins with the first egg and lasts 25-26 days. The male continues to advertise and defend the nesting territory through several months, through June–July in Europe.

Eggs hatch very asynchronously. In a large clutch the last egg may hatch 12 or 13 days after the first, and these last eggs often fail to hatch. Young are semialtricial and nidicolous. They are cared for by the female. Polygamous males play no part in the rearing of the young. They are driven away by the female should they approach the nest. In monogamous pairs, the male may bring food near to the nest for the female to use. Vary rarely, the male joins the female on the feeding grounds. Food is regurgitated into the nest. Large prey not consumed by the young is often re-consumed by the parent. After 15-20 d, the young are fed off the nest site.

The young soon become very active, exhibiting various self-defence attitudes and actions. They clamber from the nest and through the reeds after the first week. They fledge at 50-55 days. Breeding success in one study in Germany was 56% reared to 14 days.

Population dynamics

Bitterns first breed as early as one year. Populations in which some birds remain north in winter can suffer significant mortality in hard winters, up to 40-80% (Marion et al. 2000). After a winter kill in the early 1960's, nesting sites were never reoccupied. In Sweden the population declined from 450 to 270-300 pairs after a hard winter and the populations needed 3-7 years to recover (Marion et al. 2000). Normal juvenile or adult mortality, or the role of migration is not known. Longevity is 9 years.

Conservation

The population in Europe has been in decline for many years. An original contributing factor was habitat alteration, mainly through drainage and human persecution. In some countries protective measures brought back the population by the middle of the last century, but in the past 30 years the decline has resumed. Although factors are unclear, it is likely that core to the decline is the continued loss of Phragmites marshes. Conservation activities in Europe need to concentrate on these habitats. In evaluating the decline of European bitterns, it is important to consider that similar declines are occurring in other large bitterns. Whereas habitat alteration is clearly involved in some areas, such in west Australia, causes remain puzzling in other areas such as New Zealand, and large-scale climatic events appear to be implicated elsewhere, such as in North America. The long-term and short-term impact of winter mortality on populations is clear (Bibby 1981). Information on the trend of the Eurasian Bittern in east Europe and Asia is important to begin distinguishing among causal possibilities.

The HSG considers the European and North African population to be Regionally Vulnerable (Hafner et al. 2000). Habitat loss, management practices that fail to maintain the habitat characteristics needed by bitterns, disturbance by humans, and pollution have been implicated in the declining status of the bittern in Europe (Marion et al. 2000). Human disturbance is pervasive in Europe. Cane cutting, recreation, motor vehicles, hunters, and boats all disturb nesting bitterns (Day and Wilson 1978, Newton et al. 1994, Tyler et al. 1998, Whiteside 1989, Piskorski 1999). Protection and management of important bittern habitats are needed across its European range. Fortunately research is demonstrating appropriate approaches (Bibby and Lunn 1982, Tyler 1994, Hobbs 1995, Welch 1995, Vicens 1997, Puglisi et al. 1995b, Dvorak et al. 1997, Tyler et al. 1998, Soto-Largo et al. 1998, Schlumprecht 1999, Smith et al. 2000). Reed cutting, for example, if properly managed, can provide multiage stands desirable to the bittern, but if badly managed—such as permitting large-scale cutting in late winter-habitat quality is destroyed. Regional management schemes, monitoring, education, and local action are needed, perhaps linked to conservation of the Purple Heron in these same habitats (Hafner et al. 2000). Wintering birds remain common in Iraq and Iran. There drainage of the Mesopotamian marches is a threat to their welfare and that of other water birds that use this critical area. Information on wintering status in Africa is nearly non-existent. The southern Africa population is even more at threat, given its rapid decline over the past several decades. Conservation action in its remaining known locations in South Africa and Zambia is essential.

Research needs

There have been important advances in our understanding of the biology and conservation needs of this species. Studies should continue on the breeding, habitat needs, and demography of this species especially outside western Europe, where most information is from. Surveys are needed to determine the status and distribution of nesting of Eurasian Bitterns in southern Africa and wintering birds in northern Africa. The status and trends of the species in Russia need to be understood, not only to develop appropriate conservation strategies but also to compare with the situation in west Europe.

Overview

The Eurasian Bittern is a skulking species seldom seen far from its reed-bed habitat. It spends most of its time Walking very slowly, but covering large distances around its feeding territory. It catches what it can, with considerable specialization in different locations. The Eurasian Bittern has polygamous tendencies and exhibits lack of a parental role by the male. This means that the feeding of the chicks is left mostly to the female, the male’s role being to defend the territory and protect food supplies for the female. The bittern has the largest span for asynchronous hatching among herons, the span of ages within the brood perhaps serving to separate periods of high energy demand among the siblings. Much remains to be understood about the biology of polygamy in bitterns.