Australasian Gannet Morus serrator Scientific name definitions

84–91 cm; c. 2350 g; wingspan 160–170 cm. Adult has head and neck with rich apricot to golden tinge fading to whitish towards throat (but see bare parts), lower neck and forehead, otherwise entirely white except for black primaries , secondaries , alula, greater and median primary upperwing coverts and a few outermost greater secondary upperwing coverts, the tail has two (sometimes more) central pairs of rectrices black, these and primaries with noticeable whitish shafts; undersurface of primaries and secondaries greyer, palest at primary bases; iris steel grey with paler narrow inner ring, or silvery grey to whitish; naked cerulean blue to cobalt blue eyering surrounded by small mask of black skin narrowly surrounding the entire base of bill, broadest on loral region, and running also along chin and central throat; bill lead-grey, often with a slight yellowish or greenish tinge, has a thin black line between culminicorn and latericorn, cutting edges also narrowly black; legs greyish black with noticeable pale greenish yellow toe ridges running upwards through anterior side of tarsus. Sexes similar. At two colonies in S Australia females were slightly heavier and with a longer ulna than males (1 Angel, L.P., Wells, M.R., Rodríguez-Malagón, M.A., Tew, E., Speakman, J.R. and Arnould, J.P.Y. (2015). Sexual size dimorphism and body condition in the Australasian Gannet. PLOS One. 10(12): e0142653. Close ). Juvenile has head and neck densely spotted white and blackish brown, the white often predominates, rest of upperparts including wing and tail dull blackish brown, each feather with an obvious white spot at tip, flight feathers and tail also white-tipped, obviously so on secondaries (narrow white trailing edge), the white tips becoming more extensive on rump, the exposed uppertail-feathers largely white, underwing coverts white except a variable number of dark median secondary coverts and a few lesser, the lesser primary coverts are dark with white spots and the median ones are largely dark with paler subterminal spots, forming a large dark carpal patch, bases of primaries paler grey than rest of flight feathers (except for the white tips), dark spots often more or less coalescent on upper chest, abdomen to undertail-coverts largely white, iris grey; bill dark brownish grey, legs dull brownish; attains adult plumage after a series of immature transitional stages, as described in previoius species. Very like <em>M. bassanus</em> and <em>M. capensis</em> in general appearance , the adult may be told from the former by black secondaries and central tail, and often by more saturated colours on eyering and head (great individual variation, however), from the latter by white tail with black centre (but some individuals with all-black tail are indistinguishable, and a few M. capensis may have some white at sides of tail too); subadult birds are difficult to tell from M. bassanus but all of the secondaries are black, possibly not distinguishable from those of M. capensis if not for larger white spots on dark feathers; juvenile in its first plumage easily told by much white on head and mostly white underparts, the upperparts also more patterned, with noticeably larger white spots forming rows or a pale central panel on upperwing.

Breeds on coasts of SE Australia, Tasmania and New Zealand; also small colony at Norfolk I. Winters on adjacent waters and up W & E coasts of Australia as far as Tropic of Capricorn.

Strictly marine ; wanders over continental shelf or inshore waters, seldom far from land. Breeds on open offshore islets  and in some protected mainland sites, as Cape Kidnappers and Muriwai Beach in New Zealand.

Most adults stay within vicinity of colony after breeding. Young disperse: those from New Zealand move W across Tasman Sea to S Australian waters, where ringing results have shown that they may cover 2600 km in a week; large numbers follow W & E coasts of Australia N as far as Tropic of Capricorn. Since 1982, and up to the present day, a number of individuals have appeared at colonies of the Cape Gannet off S Africa (4 Dyer, B. M. (1990). Eight new records of the Australasian Gannet Morus serrator in South Africa. Marine Ornithology. 18: 60–64. Close ) and, at least once, off Namibia (5 Dyer, B. M. (1995). First record of the Australasian Gannet Morus serrator for Namibia. Marine Ornithology. 23: 158. Close ).There is one record from southern Brazil (6 Bege, L. A. R. and Pauli, B. T. (1990). Two birds new to the Brazilian avifauna. Bull. Brit. Orn. Club. 110(2): 93–94. Close ). Satellite tracking of ten fledglings from Cape Kidnappers gannetry , on North I (New Zealand), suggested that those leaving colony initially landed on sea; a male and two females moved S along E coast to S tip of New Zealand, the females then crossing Tasman Sea to E Australian coastal waters in 4 and 5 days, respectively, probably because, contrary to older reports, route via Stewart I constitutes a better migration path for fledglings from Cape Kidnappers (minimizing distance travelled across open sea to SE Australia or Tasmania) (7 Ismar, S. M. H., Hunter, C., Lay, K., Ward-Smith, T., Wilson, P. R. and 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(3): 755-759. DOI 10.1007/s10336-010-0504-1. Close ); initial direction of flight need not be indicative of subsequent route taken. In a further study at this colony, geolocation sensor tags were used to track adults from Cape Kidnappers to Australia during non-breeding period in order to assess the species’ wintering behaviour and migration routes; data from three recovered tags indicated that a male and a female (and also a hybrid between this species and M. capensis) migrated across Tasman Sea to winter quarters in coastal waters of Australia and Tasmania, tracked individuals having covered distances of up to 13,000 km on migration, and movements being consistent with earlier records of ringing recoveries (8 Ismar, S. M. H., Phillips, R. A., Rayner, M. J. and Hauber, M. E. (2011). Geolocation tracking of the annual migration of adult Australasian Gannets (Morus serrator) breeding in New Zealand. Wilson Journal of Ornithology. 123(1): 121-125. Close ).

Mostly pelagic fish, especially pilchard (Sardinops neopilchardus), anchovies (Engraulis australis) and jack mackerel (Trachurus novaezelandiae); also garfish (Hyporhamphus ihi), other fish and some squid (Nototodarus). Birds nesting at the Australian colonies, in the south-east of the country and off Tasmania, breed in cool temperate coastal waters where the the chief prey is the pilchard (Sardinops sagax) as well as other small pelagic schooling fish and squid (9 Bunce, A. (2001). Prey consumption of Australasian gannets (Morus serrator) breeding in Port Philip Bay, south-east Australia and competition with commercial fisheries. ICES Journal of Marine Science. 58: 904–915. Close ). Prey caught by plunge-diving . Also attends trawlers regularly. A special study of this species’ prey-catching behaviour appears to provide first demonstration of a plunge-diving bird’s capacity for visual accommodation underwater while capturing submerged prey detected from air: in analyses of 55 minutes of underwater video footage for evidence that gannets use vision in aquatic phases of hunting, photokeratometry and infrared video photo-refraction revealed that, immediately the gannet’s head became submerged, its eyes accommodated for (and overcame) the loss of more than 45 dioptres of corneal refractive power (which occurs in transition between air and water); also that prey-capture rates were highest during the wing-flapping phase when the birds actively pursue individual fish, behaviour very likely to involve visual guidance, following transition after the momentum phase of the plunging descent through the water column (10 Machovsky-Capuska, G. E., Howland, H. C., Raubenheimer, D., Vaughn-Hirshorn, R., Würsig, B., Hauber, M. E. and Katzir, G. (2012). Visual accommodation and active pursuit of prey underwater in a plunge-diving bird: the Australasian gannet. Proc. Royal Soc. London (Ser. B Biol. Sci.). 279(1745) 4118-4125. Close ).In recent investigation of possible fatal injuries caused by collision with conspecifics during plunge-diving, post-mortem examinations of carcasses recovered from New Zealand waters revealed evidence that such collisions likely to have been cause of death (11 Machovsky Capuska, G. E., Dwyer, S. L., Alley, M. R., Stockin, K. A. and Raubenheimer, D. (2011). Evidence for fatal collisions and kleptoparasitism while plunge-diving in Gannets. Ibis. 153(3): 631-635. Close ).

Commonest call is a rather distinctive "urrah-urrah", male clearly higher-pitched than female. It is also reported to be higher pitched than the equivalent call of the Cape Gannet and the call has sometimes drawn attention to vagrant Australian Gannets that have appeared within Cape Gannet colonies.Various other sounds, including "yorr" during sky-pointing display. Much individual variation in vocalizations.

Highly seasonal, Oct–May. Ground-nester , commonly in rather small but dense colonies . Nest a rough mound of seaweed and grass, cemented together by excreta. Clutch 1 egg, exceptionally 2; incubation period c. 44 days; chick has white down on whitish skin; fledging period c. 102 days. In study of Pope’s Eye colony in Port Phillip Bay (Victoria), in SE Australia, in 15 of 19 years between 1988 and 2006–2007, total of 2516 eggs recorded, resulting in 1694 chicks hatching (67% of eggs), and in 1310 young (77% of hatchlings) inlinemedia; at least 184 (14%) of the inlinemedia returned to colony as breeding adults (12 Pyk, T. M., Weston, M. A., Bunce, A. and Norman, F. I. (2013). Establishment and development of a seabird colony: long-term trends in phenology, breeding success, recruitment, breeding density and demography. Journal of Ornithology. 154(1): 299-310. DOI 10.1007/s10336-012-0894-3. Close ). Age of first breeding 5–6 years. Known to have lived for more than 33 years in the wild; annual mortality rate of adults c. 5%. At least one of the Australasian Gannets that have appeared at Cape Gannet colonies off S Africa formed a mixed pair with one of the latter for four successive breeding seasons, fledging a hybrid young on the last occasion, in 1997 (13 Dyer, B. M., Upfold, L., Kant, W. and Ward, V. L. (2001). Breeding by and additional records of Australasian Gannet, Morus serrator, in South Africa. Ostrich. 72: 124-125. Close ).

Not globally threatened (Least Concern). Numbers were greatly reduced by human persecution during first half of 20th century after which the population increased markedly, both in Australia and New Zealand . Population still slightly increasing at present, but still the least numerous of gannets, with total breeding population estimated at c. 53,000 pairs in 1980 (more than 80% in New Zealand waters) and perhaps c. 75,000 pairs in early years of 21st century. The Australian population increased from 6,600 pairs in 1980–81 to 20,000 pairs by 1999–2000 and it has been suggested that a significant trend towards more frequent, and stronger, El Niño events, warmer summer sea temperatures in the Bass Strait, and increased commerical catches and discards by the Victorian Pilchard (Sardinops sagax) fishery may account for some of the increase in the Australian breeding birds (14 Bunce, A., Norman, F. I., Brother, N. and Gales, R. (2002). Long-term trends in the Australasian gannet (Morus serrator) population in Australia: the effect of climate change and commercial fisheries. Marine Biology. 141: 263–269. Close ). Colonies off Tasmania have declined markedly. About 33 gannetries known, some established only very recently; small colony of 1–3 pairs established in 1974 on Philip I, by Norfolk I in N Tasman Sea. In SE Australia, colony at Pope’s Eye, within Port Phillip Bay (Victoria), was established in 1984 on an artificial structure, and in that first year held 25 nests; thereafter, number and density of nests increased, nests by 8·8% annually, and density at varying rates in different parts of colony; early recruits were from a nearby colony, but within five years of initial establishment the first natal recruits were breeding at Pope’s Eye, and from that time natal recruitment was main source of new breeding adults (accounting for 81·4% of all recruits); rapid initial growth is typical of patterns reported for other seabird colonies, but, as colony (and its occupants) aged, no increase in breeding success was noted nor did egg-laying become earlier, contrary to pattern expected from general models of colony development (12 Pyk, T. M., Weston, M. A., Bunce, A. and Norman, F. I. (2013). Establishment and development of a seabird colony: long-term trends in phenology, breeding success, recruitment, breeding density and demography. Journal of Ornithology. 154(1): 299-310. DOI 10.1007/s10336-012-0894-3. Close ). Now legally protected at colonies, but eggs and chicks still taken at a few. Sometimes caught accidentally during fishing activities. There have been repeated observations and records of attempted nesting by this species, in the company of occasional Cape Gannets, on St Paul's Island in the southern Indian Ocean, some 4,000km away from the normal range of both species (15 Lequette, B., Berteaux, D. and Judas, J. (1995). Presence and first breeding attempts of southern gannets Morus capensis and M. serrator at Saint Paul Island, southern Indian Ocean. Emu. 95: 134–137. Close ): up to six Australasian Gannets were recorded at a time, eggs have been laid and some chicks hatched.