Black-backed Bittern

The Black-backed Bittern, scientifically known as Ixobrychus dubius, is a diminutive heron species, one of the smallest in the world, with a length ranging from 25 to 36 cm and a weight between 60 to 120 grams. The adult male is characterized by predominantly black upperparts, including a black cap, and rich chestnut underparts, neck, breast, and sides of the head. It also features large buff patches on the shoulders, which are particularly noticeable in flight. The female presents a more subdued appearance with brown and streaked back and crown, while immature birds bear a resemblance to the female. The eyes are yellow, the bill is yellow with a black culmen, and the legs and feet are greenish-yellow.

Identification Tips

When identifying the Black-backed Bittern, look for the male's distinctive black back and cap, as well as the chestnut coloring on the underparts. The large buff patches on the shoulders are a key feature to observe, especially when the bird is in flight. Females and juveniles can be identified by their duller, streaked appearance. The yellow eyes, yellow bill with a black culmen, and greenish-yellow legs and feet are also identifying characteristics.

Habitat

This species is primarily associated with freshwater wetlands, where it occupies dense emergent vegetation such as reeds and sedges, as well as inundated shrub thickets. It can also be found in brackish and saline wetlands, including mangrove swamps, salt marshes dominated by Juncus, and the wooded margins of coastal lagoons.

Distribution

The Black-backed Bittern is native to Australia and is a vagrant to southern New Guinea. In Australia, it is predominantly found in the south-east, particularly in the Murray-Darling Basin, along the east coast, and in south-west Western Australia. It has also been recorded in the Kimberley region, the Top End, the Torres Strait islands, and occasionally as a vagrant to Lord Howe Island and New Zealand.

Behaviour

This species is known for its solitary and secretive nature, being most active at dusk or night. It is adept at skulking through reed beds, adopting a crouched posture with its head extended forward. When alarmed, it will freeze and point its bill vertically upwards to blend in with the surrounding vegetation. Flight is usually a last resort, characterized by a low, skimming motion over water and vegetation.

Breeding

Breeding occurs in spring and early summer. The Black-backed Bittern nests in dense wetland vegetation, constructing a platform of reeds and other plant matter over water. Clutches typically consist of four to six matt white eggs, incubated for about 21 days. Chicks are covered in orange-buff down and are fed by both parents through regurgitation.

Diet and Feeding

The diet consists mainly of aquatic invertebrates, including crustaceans and dragonfly larvae, and occasionally small vertebrates like fish and frogs. The Black-backed Bittern employs a sit-and-wait strategy or active stalking to capture prey.

Song & Calls

The vocalizations of the Black-backed Bittern are not well-documented. Outside of breeding season, they are generally silent, but may produce low croaking or grunting sounds. During breeding season, males emit a deep, low, monotonous croaking call at half-second intervals.

Conservation status

The Black-backed Bittern is listed as Near Threatened in Australia and Endangered in Victoria. The global population is estimated at around 5000 mature individuals, with threats including habitat degradation due to salinisation, drainage, water diversion for irrigation, and destruction of nesting habitats by inappropriate burning practices.