While the black swan may be found singly, it is also often seen in loose groups comprising several hundred or even thousands of individuals. When on the ground, a large group of black swans is known as a ‘bank’, whereas in flight it is known as a ‘wedge’ (7). Black swans residing in areas of suitable permanent habitat are sedentary (2) (3), while those inhabiting more temporary waters are known to be nomadic, wandering extensively in response to droughts or rainy periods (2) (3) (7).
The black swan’s diet is composed almost entirely of vegetable matter, with this species feeding on a variety of aquatic plants and algae (2), including sea grasses (10). The black swan usually finds its food by upending or by dabbling on the surface, although it is also known to graze in dry pastures and flooded fields (2).
The black swan’s breeding season appears to vary with location (2). However, it generally occurs in the wetter winter months, from February to September (7), when water levels are at their highest (2). This species nests in colonies (2) (7), and like other swans it is largely monogamous, usually pairing for life. If one bird of the pair should die, the other black swan will usually not attempt to find another mate (7).
Both the male and the female black swan take part in building the nest (7), which is a large mound of reeds, grasses and weeds that either floats on the water or is placed on the ground (2) (7). The nest is reused year on year, or is restored or rebuilt as required (7). The female black swan lays a clutch of between 4 and 6 greenish-white eggs, which are incubated for a period of 35 to 40 days (2) (7). The chicks hatch covered in light grey down (2), and are tended by both adults for a period of about six months, during which time they may ride on the backs of the adults during ventures into deeper water (7). The young black swans fledge at about 150 to 170 days old, although fledging can occur before this in years when food availability is high. The black swan reaches sexual maturity between 18 and 36 months of age (2).
Like many other waterbird species, the adult black swans lose all of their flight feathers after the breeding season, and are then unable to fly for about a month, during which time they settle on large areas of open water for safety (7).