Saturday, March 31, 2012

Australasian Darter Anhinga novaehollandiae

Conservation Status
Federal: Secure - Least Concern
NSW: Secure
NT: Secure
QLD: Secure
SA: Secure
TAS: Not present
VIC: Secure
Calls - Listen
This bird is usually quiet. Sounds during breeding season from nest
Two individuals calling
Physical description of birds:
The Darter is a large, slim water bird with a long snake-like neck, sharp pointed bill, and long, rounded tail. Male birds are dark brownish black with glossy black upperwings, streaked and spotted white, silver-grey and brown. The strongly kinked neck has a white or pale brown stripe from the bill to where the neck kinks and the breast is chestnut brown. Females and immature birds are grey-brown above, pale grey to white below, with a white neck stripe that is less distinct in young birds. The Darter is often seen swimming with only the snake-like neck visible above the water, or drying its wings while perched on a tree or stump over water. While its gait is clumsy on land, it can soar gracefully to great heights on wind thermal currents, gliding from updraft to updraft. It has a cross-shaped silhouette when flying.

In Tenterfield, the Australasian Darter is located at the Tenterfield Dam as well as at various locations along the Tenterfield Creek. The Darter seems to prefer locations that have trees near the water's edge as well as low lying branches close to the water. It can also be found at various dams on people's properties in the immediate area surrounding Tenterfield, on ocassions.

The Australasian Darter is not numerous in numbers with sightings of less than 10 individual birds at any given time.

General information

The Darter is found in wetlands and sheltered coastal waters, mainly in the Tropics and Subtropics. It prefers smooth, open waters, for feeding, with tree trunks, branches, stumps or posts fringing the water, for resting and drying its wings. Most often seen inland, around permanent and temporary water bodies at least half a metre deep, but may be seen in calm seas near shore, fishing. The Darter is not affected by salinity or murky waters, but does require waters with sparse vegetation that allow it to swim and dive easily. It builds its nests in trees standing in water, and will move to deeper waters if the waters begin to dry up.

Seasonal movements:
Darters can move over long distances (over 2000 km) when not breeding, but populations tend to contract to breeding areas during summer.

The Darter catches fish with its sharp bill partly open while diving in water deeper than 60 cm. The fish is pierced from underneath, flicked onto the water's surface and then swallowed head first. Smaller items are eaten underwater and large items may be carried to a convenient perch and then swallowed. Insects and other aquatic animals, including tortoises, may also be eaten, as well as some vegetable matter. In hot weather, adult birds may pour water from their bills into the gullets of their young chicks when they are still in the nest.

The Darter is usually a solitary bird, forming pairs only while breeding. Breeding is erratic, happening whenever water levels and food supplies are suitable, but most often occurs in spring and summer. Nests are usually solitary, but Darters may nest within loose colonies with other water birds that nest in trees, such as cormorants, spoonbills and ibis. The male decorates a nest-site with green leafy twigs and displays to attract a mate, with elaborate wing-waving and twig-grasping movements. The male carries most of the nest material to the nest-site, which is normally in the fork of a tree standing in water, usually about 3.5 metres above the water's surface. Both sexes complete the nest, incubate the eggs and raise the young. Chicks are kept warm by brooding continously (or cooled down by shading with spread wings) for up to a week after hatching and both adults stay in the nest with the chicks overnight. In hot weather, the adults will even shake water over the chicks after a swim. Chicks can swim after about four weeks in the nest and start to fly at about 50 days.

Living amongst humans
Although the deep, open water bodies that Darters favour suffer less from drainage than other wetland types, Darters are still threatened by increased salinity, clearing, grazing, increased fire frequency and extraction of groundwater. Because Darters often feed on introduced fish species such as Carp and Redfin Perch, they may be adversely affected by attempts to reduce numbers of these fish species. Darters are also often casualties of duck-shooting, with birds being shot or disturbed from their nests and losing their eggs to ravens. Adults may also drown if trapped in fishing nets.

Slideshow of Australasian Darter images


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