Australasian Gannet

An adult Australasian gannet is 84–91 cm (33–36 in) long, weighs 2.3 kg (5.1 lb), and has a 170–200 cm (67–79 in) wingspan. The two sexes are generally of a similar size and appearance, though a 2015 field study at Pope's Eye and Point Danger colonies found females to be 3.1% and 7.3% heavier respectively. Females also had a slightly larger ulna and smaller bill. The plumage is white with black flight feathers on the wings, and central rectrices of the tail. Some individuals have more extensive black plumage of their tail feathers. There is a sharp demarcation between light and dark plumage. Black primary feathers are more resilient to wear, which may explain the dark plumage of the wings. The head and hindneck are tinged buff-yellow. The colour is more pronounced on the head and during breeding season. The eyes have a light grey iris surrounded by a pale blue eye ring, and bare black skin on the face which merges into the bill. In adults, the bill is pearly grey with dark grey or black edges, and a black groove running down the length of the upper mandible. The four-toed feet are dark grey and joined by a membrane of similar colour. There are light green lines running along the ridges of the toes that continue along up the front of the legs.

Fledglings are brownish-grey speckled with white overall. …

The Australasian gannet is found from Steep Point in Western Australia, along the southern and eastern Australian coastline to the vicinity of Rockhampton in Queensland, as well as the North and South Islands of New Zealand, Lord Howe and Norfolk Islands. At sea, it is generally restricted to waters over the continental shelf, and may enter harbours, bays and estuaries, particularly in stormy weather. Over May and June, young gannets from New Zealand colonies disperse to the north and west, mainly flying north around the North Island and (to a lesser extent) via the Cook Strait. They generally reach as far as southeastern Queensland and Rottnest Island in Western Australia. Far-wandering gannets are occasional visitors to Marion Island and the Crozet Islands in the southern Indian Ocean, and have even reached South Africa where they have interbred with Cape gannets. Some immature gannets spend 3 to 4 years in Australian waters before returning to New Zealand, while others remain in New Zealand waters.

Breeding colonies. Breeding colonies are mostly on offshore islands, though several mainland colonies exist in Australia and New Zealand. Numbers of Australasian gannet have been increasing since 1950, although some colonies have disappeared and others have decreased in size. …

The Australasian gannet is generally solitary when out at sea, though once a bird has found fish to hunt, other gannets may notice and join it. It is gregarious on land, nesting in colonies. Non-breeding gannets often form groups on the outskirts of the colony. Small numbers of gannets may remain around the colony site outside of the breeding season, using it as a roosting site.

Breeding and courtship. Gannet pairs form monogamous and long term bonds, and pairs may remain together over several seasons until one member dies, although they have been known to separate. The Australasian gannet is highly territorial when nesting, engaging in agonistic displays to mark their ground against neighbours and interlopers. In the bowing display, the male's head and beak point down, and its wings are held up and away from the body, yet folded backwards. He moves his head from side to side before bowing forwards. The male may escalate by lunging at an interloper, either with a closed or open bill, or proceed to locking bills and wrestling for an extended period. Fights can be fatal on occasion. A bird may engage in an appeasement display to calm an attacker by lowering its head and tucking its bill in its chest.

Mated pairs engage in a fencing display when the male arrives back at the nest. The two birds stand breast to breast with wings spread and bills extended vertically. …