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.

Sir Joseph Banks shot three Australasian gannets in New Zealand waters on 24 December 1769 off Three Kings Islands.

[3] 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.

[3] "Australasian gannet" has been designated as the official common name for the species by the International Ornithologists' Union (IOC).

Early Sulidae fossils most resembled the boobies, although they were more aquatic, the gannets splitting off later, about 16 million years ago.

[11] 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 two sexes are generally of a similar size and appearance,[14] though a 2015 field study at Pope's Eye and Point Danger colonies found females to be 3.1% and 7.3% heavier respectively.

Over this period, the upperparts and underparts gradually whiten and the crown and nape become buff-coloured, but there is great variation in the age that mature plumage is seen.

[16] The Australasian gannet is generally silent at sea and loud and vocal at the colony in the day and at times overnight during the breeding season.

[19] At sea, it is generally restricted to waters over the continental shelf,[16] and may enter harbours, bays and estuaries, particularly in stormy weather.

[22] In Victoria, there are colonies at Lawrence Rocks near Portland, and Pope's Eye and Wedge Light in Port Phillip near Melbourne.

[22] Located 5 kilometres (3.1 mi) northeast of Portsea, Pope's Eye is a low artificial semicircular stone breakwater.

[22] Conversely, the colony at Cat Island fell from an estimated 5–10,000 pairs in 1908 to negligible numbers by the turn of the millennium due to predation.

[30] On the South Island, gannets began breeding at the end of Farewell Spit in 1983, in an area known as Shellbanks—a 2 m (7 ft) high area of shells and driftwood interspersed with low vegetation: marram (Ammophila arenaria), sea rocket (Cakile edentula), velvety nightshade (Solanum chenopodioides) and sowthistle (Sonchus oleraceus).

[34] The Australasian gannet is highly territorial when nesting, engaging in agonistic displays to mark their ground against neighbours and interlopers.

[34] 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.

Mated pairs also engage in sky-pointing, where a bird paces slowly with its neck and bill vertical and its wings partly raised.

[35] Copulation takes place after allopreening, the female shaking her head vigorously and the male biting her neck and climbing on her back and waving his wings before joining their cloacae.

At Cape Kidnappers, the gannets return in late July, laying eggs from early September to the end of October.

[21] At Pope's Eye, gannets lay eggs between early August and December, the median and mean being laid in September.

[21] The nests themselves are cup-shaped mounds 10–20 centimetres (3.9–7.9 in) high with a 30 cm (12 in) deep basin, made from seaweed, plants, earth and debris from the sea.

[21] The maximum age recorded from banding has been 30 years 8.2 months; a bird tagged at Cape Kidnappers in January 1955 was found dead some 2,587 km (1,607 mi) away at Tangalooma in Moreton Bay, Queensland in September 1985.

The longest distance travelled is 8,128 km (5,051 mi); a bird tagged at Lawrence Rocks was found washed ashore dead on the southeast coast of Mauritius.

[42] The pilchard (Sardinops sagax) is a preferred prey item as it is an energy-rich source of food; after pilchard mass mortality events, Australasian gannets were able to adjust by switching to anchovy (Engraulis australis) at Farewell Spit in 1996 and barracouta (Thyrsites atun) in Port Phillip Bay in 1998.

[32][43] They also consumed correspondingly larger numbers of anchovies to maintain their caloric intake as this species has fewer calories than the pilchard.

The cause was unknown, but the 1995 pilchard mortality event and unusually strong westerly and southwesterly winds in July and August 1995 were implicated.

[44] Other fish species reported eaten include kahawai (Arripis trutta), yellow-eye mullet (Aldrichetta forsteri), western Australian salmon (Arripis truttaceus), cape bonnetmouth (Emmelichthys nitidus), greenback horse mackerel (Trachurus declivis), yellowtail horse mackerel (Trachurus novaezelandiae), striped trumpeter (Latris lineata), New Zealand blueback sprat (Sprattus antipodum) and flyingfish of the genera Cheilopogon and Hirundichthys.

[40] The southern giant petrel (Macronectes giganteus) has been recorded preying on an adult Australasian gannet by holding it underwater and drowning it.

[48] The International Union for Conservation of Nature (IUCN) lists the Australasian gannet as a species of least concern, as the population is large and appears to be growing.

[51] Some mainland colonies have become tourist attractions, such as those at Cape Kidnappers / Te Kauwae-a-Māui,[52] and Muriwai in New Zealand,[53] and Point Danger in Australia.