The Australasian gannet (Morus serrator), also known as the Australian gannet or tākapu, is a large seabird of the booby and gannet family, Sulidae. Adults are mostly white, with black flight feathers at the wingtips and lining the trailing edge of the wing. The central tail feathers are also black. The head is tinged buff-yellow, with a pearly grey bill edged in dark grey or black, and blue-rimmed eyes. Young birds have mottled plumage in their first year, dark above and light below. The head is an intermediate mottled grey, with a dark bill. The birds gradually acquire more white in subsequent seasons until they reach maturity after five years.
The species range over water above the continental shelf along the southern and eastern Australian coastline, from Steep Point in Western Australia to Rockhampton, Queensland, as well as the North and South Islands of New Zealand, Lord Howe and Norfolk Islands. Nesting takes place in colonies along the coastlines of New Zealand, Victoria and Tasmania—mostly on offshore islands, although there are several mainland colonies in both countries. Highly territorial when breeding, the Australasian gannet performs agonistic displays to defend its nest. Potential and mated pairs engage in courtship and greeting displays. The nest is a cup-shaped mound composed of seaweed, earth, and other debris, built by the female from material mainly gathered by the male. A single pale blue egg is laid yearly, though lost eggs may be replaced. The chick is born featherless but is soon covered in white down. Fed regurgitated fish by its parents, it grows rapidly and outweighs the average adult when it fledges.
These birds are plunge divers and spectacular fishers, plunging into the ocean at high speed. They eat mainly squid and forage fish that school near the surface. The species faces few natural or man-made threats, and since its population is growing it is considered to be a least-concern species by the International Union for Conservation of Nature (IUCN).
Taxonomy
Sir Joseph Banks shot three Australasian gannets in New Zealand waters on 24 December 1769 off Three Kings Islands. The birds were cooked in a goose pie, which was enjoyed by the sailors, for Christmas the next day. Daniel Solander wrote a formal description, noting its differences from the familiar northern gannet, initially giving it the name Pelecanus chrysocephalus before crossing it out and changing it to Pelecanus sectator. Sydney Parkinson illustrated the bird as P. sectator, which was misread as P. serrator by later authorities. The species name has been translated as "sawyer", from serra "saw", and linked to the serrated bill.
John Gould described specimens from the Derwent River and Actaeon Island in Tasmania as Sula australis in 1841. The binomial name Sula australis had already been used by J. F. Stephens for the red-footed booby. English zoologist George Robert Gray wrote of the species in 1843, initially using Gould's name but soon switching to Sula serrator, based on Parkinson's drawing. Although Gould stuck with S. australis, S. serrator became the preferred term over time.
"Australasian gannet" has been designated as the official common name for the species by the International Ornithologists' Union (IOC). It is also known as Pacific gannet and, in Australia, as Australian gannet, diver (from its plunge-diving), booby, or solan goose. In New Zealand it is also known by the Māori name tākapu or tākupu, a word of wider Polynesian origin for a gannet or booby.
The Sulidae, the gannets and boobies, appeared about 30 million years ago. Early Sulidae fossils most resembled the boobies, although they were more aquatic, the gannets splitting off later, about 16 million years ago. The gannets evolved in the northern hemisphere, later colonising the southern oceans. The most ancient extant species may be the Abbott's booby, possibly the sole survivor of an otherwise extinct separate lineage. A 2011 genetic study of nuclear and mitochondrial DNA suggests that the ancestor of the gannets arose around 2.5 million years ago before splitting into northern and southern lineages. The latter then split into the Cape and Australasian gannets around 0.5 million years ago. The three gannets are generally considered to be separate species forming a superspecies, though they have also formerly been classified as subspecies of the northern gannet (Sula bassanus).