Buller’s mollymawks are one of the more abundant small albatrosses occurring around coastal areas of New Zealand, particularly from Cook Strait south. Their striking black-and-golden-yellow bill and smart black-and-white plumage make them readily identifiable as they scavenge close to fishing vessels. The southern subspecies is unusual among albatrosses in breeding under tall, dense woody vegetation which sometimes requires it to walk up to 100 m inland to reach its nest after landing in open tussock at the forest edge.

Identification

The Buller’s mollymawk is one of the smallest of the albatrosses. It is black across the upperwings, with a white lower back and rump and black tip to the tail. The underparts are white with a clear-cut broad black leading edge and narrow black trailing edge under the wing. The light-grey neck and throat contrast with the silvery-grey crown. The bill is black with golden-yellow top and bottom plates.

The two subspecies are separated by bill size and colour and head plumage. Southern Buller’s mollymawk has a silvery-white forehead with black extending over about 70% of the sides of the bill. Northern Buller’s mollymawk has a silvery-grey forehead with black extending over about 80% of the sides of the bill. In addition, the bill of northern Buller’s mollymawk is more robust (longer and deeper) than that of the southern Buller’s mollymawk.

Voice: Buller’s mollymawks are usually silent at sea, though may give harsh croaking when squabbling for food. They utter a variety of brays, croaks and wails during courtship.

Similar species: the only similar species is the grey-headed mollymawk, which has more extensive black on the leading edge of the underwing than in Buller’s mollymawk. Also, it has a light-grey head, throat, neck and mantle that appear darker than in Buller’s mollymawk, particularly on the forehead and crown. Finally, the bill is shorter and has more extensive black on the sides than in either subspecies of Buller’s mollymawk.

Distribution and habitat

The southern subspecies breeds on the Snares Islands and the Solander Islands, with many of the nests under dense woody vegetation such as Olearia lyalli, Brachyglottis stewartiae and Hebe elliptica. During the breeding season it is commonly found in seas off the South Island and off south-eastern Australia, less often as far south as Macquarie Island and as far north as the Kermadec Islands. One was found ashore at Middle Sister Island, Chatham Islands. The northern subspecies breeds mainly in open areas on the Sisters and Forty-Fours, Chatham Islands, with a small population on Rosemary Rock, Three Kings Islands. It ranges mainly off the Chatham Islands and eastern North Island, but has been recorded in subantarctic seas. After breeding both subspecies migrate to the seas off Peru and Chile.

Population

Counts of the number of breeding pairs of southern Buller’s mollymawks estimated the total breeding population at 13,625 breeding pairs in 2002. This comprised an estimated 8,713 breeding pairs on The Snares and 4,912 breeding pairs at the Solander Islands. There are no recent estimates of the numbers of northern Buller’s mollymawks, but in the 1970s there were an estimated 16,000 breeding pairs on the Forty-Fours and 1,500 breeding pairs on Big Sister. An estimated 630-670 pairs were breeding on Little sister in 1994-96. On Rosemary Rock, 13 occupied nests were recorded in 1985. Thus, the combined total population of the two subspecies is about 32,000 breeding pairs.

Threats and conservation

All breeding sites are free from mammalian predators, although an expanding New Zealand fur seal population at the Solander Islands may be affecting breeding success of those birds breeding on the lower slopes. Buller’s mollymawk is a common albatross species observed killed in the New Zealand fisheries, with demersal longliners and trawling operations responsible for the majority of mortalities.

Breeding

Colonies can be densely packed or loose. Buller’s mollymawk are monogamous with shared incubation and chick care. The nest is a pedestal of mud, guano and vegetation accumulated from the immediate vicinity, and is used and added to year after year. The single large (104 x 64 mm) white egg is laid in October-November (northern subspecies) or January-February (southern subspecies) and hatches after 68-72 days. Chicks on the Snares Islands fledge when about 167 days old, mainly in August and September, with stragglers into October. Young are independent at fledging; they begin breeding when about 12 years old, and can live more than 45 years.

Behaviour and ecology

As a typical albatross, Buller’s mollymawks have perfected soaring flight. In strong winds they wheel effortlessly on their long, narrow, stiffly held wings. They use their webbed feet for swimming and as rudders when coming in to land. Their strongly hooked bills are used to grasp prey whilst the sharp edges of the upper mandible are used to slice it into manageable portions. However, albatrosses have a great capacity to extend the throat, and so swallow large pieces of food.

At their breeding colonies Buller’s mollymawks use an elaborate series of displays and calls to maintain their pair bond and to defend their nest pedestal. They are annual breeders that usually return to the same nest site year after year with the same partner. After breeding the colonies are deserted and the birds migrate across the Pacific to seas off Chile and Peru. Banding shows that 92-97% of adults survive from one year to the next. The oldest banded bird was estimated to be at least 54 years old.

Food

Buller’s mollymawks mainly eat fish, squid, krill, salps and offal from fishing vessels taken from the surface. They rarely plunge or dive for food.

Weblinks

BirdLife factsheet

ACAP

Wikipedia

Kingdom of the Birds: An expedition to Solander Island – Te Papa Channel

References

Francis, R.I.C.C.; Sagar, P.M. 2012. Modelling the effect of fishing on southern Buller’s albatross using a 60-year dataset. New Zealand Journal of Zoology 39: 3-17.

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

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

Robertson, C.J.R. 1991. Questions on the harvesting of toroa in the Chatham Islands. Science & Research Series 35: 1-105. Department of Conservation, Wellington.

Sagar, P.M.; Molloy, J.; Weimerskirch, H.; Warham, J. 2000. Temporal and age-related changes in survival rates of southern Buller’s albatrosses (Thalassarche bulleri bulleri) at The Snares, New Zealand, 1948-1997. Auk 117: 699-708.

Sagar, P.M.; Stahl, J.C. 2005. Increases in the numbers of breeding pairs in two populations of Buller’s albatross (Thalassarche bulleri bulleri). Emu 105: 49-55.

Sagar, P.M.; Unwin, M.J.; Stahl, J.C.; Warham, J. 2005. Variation in the size of Buller’s albatross (Thalassarche bulleri) eggs. New Zealand Journal of Zoology 32: 171-180.

Sagar, P.M.; Warham, J. 1998. Breeding biology of southern Buller’s albatross Diomedea bulleri bulleri at The Snares, New Zealand. Pp. 107-112. In Robertson, G.; Gales, R. (eds) Albatross biology and conservation. Surrey Beatty, Chipping Norton.

Stahl, J.C.; Bartle, J.A.; Cheshire, N.G.; Petyt, C.; Sagar, P.M. 1998. Distribution and movements of Buller’s albatross (Diomedea bulleri) in Australasian seas. New Zealand Journal of Zoology 25: 109-137.

Stahl, J.C.; Sagar, P.M. 2000. Foraging strategies of southern Buller’s albatrosses Diomedea b. bulleri breeding on the Snares, New Zealand. Journal of the Royal Society of New Zealand 30: 299-318.

Warham, J.; Fitzsimmons, C.H. 1987. The vocalisations of Buller’s Albatross, Diomedea bulleri, (Aves: Diomedeidae), with comparative data on other albatrosses. New Zealand Journal of Zoology 14: 65-79.

Wright, A.E. 1984. Buller’s mollymawks breeding at the Three Kings Islands. Notornis 31: 203-207.

Recommended citation

Sagar, P.M. 2013 [updated 2022]. Buller’s mollymawk | toroa. In Miskelly, C.M. (ed.) New Zealand Birds Online. www.nzbirdsonline.org.nz