With its 1.8 m wing-span, the Australasian gannet is a conspicuous, predominantly white seabird that is common in New Zealand coastal waters. They can be observed feeding solitarily or in large congregations, especially near the larger colonies. Australasian gannets breed in dense colonies on coastal islands and on cliffs and beaches of some headlands of the New Zealand mainland; the breeding distribution also encompasses south-east Australia and Tasmania.

Identification                                                                                                  

The Australasian gannet is a large, mostly coastal seabird with predominantly white plumage, long, pointed wings, a long neck and slender body shape. The trailing edges of its wings and a varying proportion of its central tail feathers are black. The wedge-shaped bill is bluish-grey, with a lining of black; the skin surrounding the eye is intensely blue. The head plumage is buff-yellow, which extends down the neck. The sexes cannot be reliably distinguished in the field. Juveniles have mottled dark brown and white plumage, and are separable from immatures, which gradually acquire more white over several moults, before acquiring full adult plumage when about 3 years old.

Voice: a distinctive ‘urrah urrah’ to announce landing, during territorial indication at the nest site, and during mutual bill fencing and bowing with the mate. Also an attenuated ‘oo-ah’ to indicate take-off. Both sexes’ calls are identical, with some locational and marked individual variation.

Similar species: the closely related Cape gannet is similar in size and appearance, and has occurred in New Zealand as a vagrant. It differs in having a longer black gular stripe extending from the chin down the throat, all its tail feathers are dark, and it has a slower, lower frequency landing call. The masked booby (which breeds on the Kermadec Islands, and occasionally strays to water off the northern North Island) is smaller, and has a yellow bill and white head.

Distribution and habitat

Australasian gannets nest in dense breeding colonies on the New Zealand mainland and coastal rocks and islands, as well as off south-east Australia and Tasmania. Although gannets can be seen occasionally from most places along the coasts of the New Zealand main islands, most gannetries are situated off the North Island. The largest mainland gannetry is at Cape Kidnappers, with around 5,000 breeding pairs. Other mainland breeding sites include Muriwai and Farewell Spit.

Australasian gannets mostly feed on waters over the continental shelf. They prefer flat ground for nesting, rather than cliff ledges. Breeding colonies are mostly situated at sites that are completely or largely surrounded by the sea, i.e. on islands or headlands.

Population

New Zealand holds the bulk of the Australasian gannet breeding population, with about 13% of the population breeding in Australia. The New Zealand population was about 46,000 pairs in 1980-81 and continued to increase at about 2% per annum, although some former breeding sites have been abandoned. Their population is probably regulated by the availability of suitable prey within easy flying distance of breeding colonies. Southern black-backed gulls take some eggs and young nestlings.

Breeding

The breeding season extends from July, when birds first return to the gannetries, to fledging in March-April. Males arrive earlier than females, and re-occupy or establish and defend a nest. From the onset of breeding, the male brings nesting material such as brown algae Carpophyllum, which he retrieves from the shallows. Both members of the pair form and maintain the nest mound, particularly when the surrounding ground is soft from rain. The single egg is produced during an asynchronous laying period that starts in August at Hauraki Gulf gannetries, and September at Cape Kidnappers. A replacement egg can be laid within 4 weeks if the first egg is lost. Laying of replacement eggs can extend into January. Rare two-egg nests may be due to two females laying in the same nest. Eggs are incubated while being held between the webbings of the gannets’ feet. The Australasian gannet can only successfully incubate a single egg. Both sexes share the incubation duty, and later brood the chick on the top of their webbed feet. Feeds are delivered by both parents as incomplete regurgitations, which the chick receives by pushing its bill into the parents’ throats.

Behaviour and ecology

Characteristic behaviours at breeding colonies include mutual bill fencing and bowing of mates at the nest, the territorial headshake and bow at the nesting site, and sky-pointing as an indication of the intention to take flight. The torpedo-like plunge dive of gannets is a spectacular sight, particularly when large foraging flocks form over surface aggregations of fish.

Fledglings from New Zealand fly directly to Australia, and typically do not return to their home colonies until their third year. Some New Zealand breeders migrate to Australian and Tasmanian waters to winter between breeding seasons. Australasian gannets often breed with the same partner over consecutive seasons. Some birds retain the same mate for the rest of their lives, but divorces do occur.

Food

Australasian gannets mainly eat fish, particularly pilchards, Australian anchovies, barracouta, garfish, mackerel and horse mackerel. Other recorded prey includes New Zealand piper, saury, flying fish, yellow-eye mullet, a puffer, and also squid.

Weblinks

BirdLife factsheet

Wikipedia

http://www.nzbirds.com/birds/takapu.html

References

Bunce, A. 2001. Effects of supplementary feeding and artificial twinning on nestling growth and survival in Australasian gannets (Morus serrator). Emu 101: 157-162.

Bunce, A. 2001. Prey consumption of Australasian gannets (Morus serrator) breeding in Port Phillip Bay, southeast Australia, and potential overlap with fisheries. ICES Journal of Marine Science 58: 904-915.

Daniel, C.; Millar, C.D.; Ismar, S.M.H.; Stephenson, B.; Hauber, M.E. 2007. Evaluating molecular and behavioural sexing methods for the Australasian gannet (Morus serrator). Australian Journal of Zoology 55: 377-382.

Friesen, V.L.; Anderson, D.J. 1997. Phylogeny and evolution of the Sulidae (Aves: Pelecaniformes): a test of alternative methods for speciation. Molecular Phylogenetics and Evolution 7: 252-260.

Heather, B.D.; Robertson, H.A. 1996. The field guide to the birds of New Zealand. Viking, Auckland.

Ismar, S.M.H. 2010. Foraging and breeding ecology of the Australasian gannet Morus serrator, with applications for rare New Zealand seabirds. PhD Thesis. University of Auckland, New Zealand.

Ismar, S.M.H.; Hunter, C.; Lay, K.; Ward-Smith, T.; Wilson, P.R.; Hauber, M.E. 2010. A virgin flight across the Tasman Sea? Satellite tracking of post-fledging movement in the Australasian gannet Morus serrator. Journal of Ornithology 151: 755-759.

Ismar, S.M.H.; Daniel, C.; Stephenson, B.M.; Hauber, M.E. 2010. Mate replacement entails a fitness cost for a socially monogamous seabird. Naturwissenschaften 97:109-113.

Ismar, S.M.H.; Phillips, R.A.; Rayner, M.J.; Hauber, M.E. 2011. Geolocation tracking of the annual migration of adult Australasian gannets Morus serrator breeding in New Zealand. The Wilson Journal of Ornithology 123: 121-125.

Krull, C.R.; Ranjard, L.; Landers, T.J.; Ismar, S.M.H.; Matthews, J.L.; Hauber, M.E. 2012. Analyses of sex and individual differences in the vocalizations of Australasian gannets using a dynamic time warping algorithm. Journal of the Acoustical Society of America 132:1189-98.

Marchant, S.; Higgins, P.J. (eds.), 1990. Handbook of Australian, New Zealand and Antarctic birds. Ratites to Ducks, vol. 1. Melbourne, Oxford University Press.

Matthews, J.-L.; Ismar, S.M.H.; Hauber, M.E. 2008. Seaweed provisioning behaviour confers thermal benefit for nesting Australasian gannets (Morus serrator). Behaviour 145: 1823-1837.

Moore, L.B.; Wodzicki, K.A. 1950. Plant material from gannets’ nests. Notornis 4: 12-13.

Nelson, B. 1978. The Sulidae: gannets and boobies. Oxford University Press, London, UK.

Nelson, B. 2002. The Atlantic gannet. 2nd edition, Fenix Books Ltd, Great Yarmouth, Norfolk, U.K.. In association with the Scottish Seabird Centre, The Harbour, North Berwick, U.K.

Parkinson, B. 2006. Field guide to New Zealand seabirds. Tim Lovegrove (ed.), New Holland Publishers (NZ) Ltd. Auckland, New Zealand.

Robertson, C.J.R. 1964. Observations on black-backed gull predators at the Cape Kidnappers gannetries: 1959-1963. Notornis 10: 393-403.

Robertson, C.J.R.; Stephenson, B.M. 2005. Cape gannet (Sula capensis) breeding at Cape Kidnappers, New Zealand. Notornis 52: 238-242.

Robertson, H.A.; Heather, B.D. 2001. The hand guide to the birds of New Zealand. Oxford University Press, Oxford, U.K.

Stein, P. 1971. Horuhoru revisited. Longevity of the Australasian gannet. Notornis 18: 310-365.

Stein, P.A.S.; Wodzicki, K.A. 1955. Dispersal of New Zealand gannets. Notornis 6: 58-64.

Stephenson, B.M. 2005. Variability in the breeding ecology of Australasian gannets, Morus serrator, at Cape Kidnappers, New Zealand. PhD Thesis. Massey University, New Zealand.

Warham, J. 1958. The nesting of the Australian gannet. Emu 58: 339-369.

Wingham, E.J. 1984. Breeding biology of the Australasian gannet Morus serrator (Gray) at Motu Karamarama, Hauraki Gulf, New Zealand I. The Egg. Emu 84: 129-136

Wingham, E.J. 1984. Breeding biology of the Australasian gannet Morus serrator (Gray) at Motu Karamarama, Hauraki Gulf, New Zealand II. Breeding success and chick growth. Emu 84: 211-224.

Wingham, E.J. 1985. Food and feeding range of the Australasian gannet Morus serrator (Gray). Emu 85: 231-239.

Wodzicki, K.A. 1967. The gannets at Cape Kidnappers. Transactions of the Royal Society of New Zealand 8: 149-162.

Wodzicki, K.; McMeekan, C.P. 1947. The gannet on Cape Kidnappers. Transactions of the Royal Society of New Zealand 76: 429-452.

Wodzicki, K.A.; Moreland, J. 1966. A note on the food of New Zealand gannets. Notornis 13: 98-99.

Wodzicki, K.; Robertson, C.J.R.; Thompson, H.R.; Alderton, C.J.T. 1984. The distribution and number of gannets (Sula serrator) in New Zealand. Notornis 31: 232-261.

Recommended citation

Ismar, S.M.H. 2013 [updated 2022]. Australasian gannet | tākapu. In Miskelly, C.M. (ed.) New Zealand Birds Online. www.nzbirdsonline.org.nz