AppearanceThis species measures from 25 to 36 cm , has a total weight of 60–120 g , averaging 84 g . This is a very small bittern and one of the smallest herons in the world. The adult male has largely black upperparts, including a black cap, while the underparts, as well as the neck, breast and the sides of the head, are rich chestnut. There are large buff patches on the shoulders, conspicuous in flight. The female is duller, brown and streaked on back and crown; immature birds are similar. The irides are yellow, the bill is yellow with a black culmen, and the feet and legs greenish-yellow.
StatusBlack-backed bitterns are listed as Near Threatened nationally in Australia, and as Endangered in Victoria. The global population has been estimated to comprise about 5000 mature individuals, mainly within Australia, including a sub-population of more than 1000 individuals in south-western Western Australia. Threats include various ongoing wetland degradation factors such as salinisation, drainage and the diversion of water for irrigation, as well as the destruction of nesting habitat by inappropriate burning regimes.
BehaviorBlack-backed bitterns are solitary, secretive and seldom seen, mainly active at dusk or at night. They are skulkers of reed beds, walking in a crouched posture with head extended forward, crossing patches of open ground rapidly, stalking their prey at the water’s edge. When alarmed they will assume the cryptic posture typical of many bitterns, standing still with the head and bill extended vertically upwards. Usually reluctant to fly, when flushed they will do so with retracted head and dangling legs, skimming low over the water and the wetland vegetation.
HabitatThe birds are mainly found in freshwater wetlands, where they inhabit dense emergent vegetation of reeds and sedges, and inundated shrub thickets. They are also occasionally found in brackish and saline wetlands such as mangrove swamps, ''Juncus''-dominated salt marsh and the wooded margins of coastal lagoons.
ReproductionThe bitterns breed in spring and early summer, nesting in single pairs, or occasionally in loose colonies with the nests 15–30 m apart, in dense wetland vegetation. The nest is a platform of reeds and other plant matter, about 15–20 cm across and 10 cm thick, supported by the vertical stems of growing reeds, always situated over water and where there is overhead cover. The clutch usually comprises four to six matt white eggs, with an incubation period of about 21 days. The chicks are covered with orange-buff down and are fed by regurgitation by both parents. Young birds may start clambering in the reeds from 9–10 days old, taking their first flight when 25–30 days old, and remaining dependent on their parents for at least another 14 days.
FoodThe birds feed mainly on aquatic invertebrates such as crustaceans and dragonfly larvae, sometimes small vertebrates such as fish and frogs. They hunt by waiting for potential prey animals to come within range of their bills, or by active stalking.
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