Red-billed gull

Larus novaehollandiae Stephens, 1826

Order: Charadriiformes

Family: Laridae

New Zealand status: Native

Conservation status: Nationally Vulnerable

Other names: silver gull, tarāpunga, tarapunga, mackerel gull, Jackie (Chathams), akiaki, seagull, redbilled gull, red billed gull

Geographical variation: Recent genetic research found five populations: 1) New Zealand (L.n. scopulinus), 2) Campbell Island (L.n. scopulinus), 3) New Caledonia (L. n. fosteri), 4) south-east Australia (L. n. novaehollandiae), 5) western Australia (L. n. novaehollandiae)

Red-billed gull. Adult. Waikanae River Estuary, Wellington, September 2010. Image © Alan Tennyson by Alan Tennyson Alan Tennyson

Red-billed gull. Adult. Waikanae River Estuary, Wellington, September 2010. Image © Alan Tennyson by Alan Tennyson Alan Tennyson

The red-billed gull is the commonest gull on the New Zealand coast. Except for a colony at Lake Rotorua, it rarely is found inland. It is commonly seen in coastal towns, garbage dumps and at fish processing facilities. Immature adults are often confused with the closely related black-billed gull. Recently the largest colonies in different parts of New Zealand have exhibited a marked decline in numbers (i.e. Kaikoura, Three Kings and Mokohinau Island). The bird tends to nest at the same locality from one season to the next, and offspring mostly return to their natal colony to breed.

Identification                                                                                       

Sexes are similar, but males are slightly larger with a longer and stouter bill. They are almost completely white but the mantle, back and wing coverts are pale grey. The main flight feathers are black with white tips. The iris is white and the bill, eyelids and feet are scarlet, especially in the breeding season, being more dull during the rest of the year. Immatures are similar to adults, except they have brown patches on the mantle and the primaries are brownish in colour rather than black. The iris, bill and legs of immatures are dark brown. Adult plumage is attained in the second year; birds of this age class can be recognised by the brownish-black tip to the bill, and the primary feathers have a brownish tinge instead of black in older individuals. The subantarctic race is stouter.

Voice: a wide range of calls are used in different circumstances. The alarm call used during the breeding season is a strident "kek" call

Similar species: the red-billed gull is often confused with the similar-looking black-billed gull, especially as juveniles and immature birds of both species have an overlapping range of bill and leg colours. The black-billed gull is always a paler, more elegant bird, with a longer, more slender bill, and with less black on the outer wing. In the South Island, the black-billed gull is seen inland more frequently than the red-billed gull.

Distribution and habitat

Red-billed gulls are found in most coastal locations throughout New Zealand. They are also commonly found in towns, scavenging on human refuse and offal from fish and meat processing works. They are seldom found inland. On mainland New Zealand, breeding occurs in dense colonies, mainly restricted to the eastern coasts of the North and South Islands on stacks, cliffs, river mouths and sandy and rocky shores. On outlying islands they breed on the Chatham, Campbell, Snares and Auckland Islands. Here, their nests are concealed and located singly or in small groups.

Population

The red-billed gull is a very abundant species that has recently suffered huge declines at its three main breeding colonies (Three Kings Islands, Mokohinau Islands and Kaikoura Peninsula). At Kaikoura the decline began in 1994, and between 1983 and 2005 the population declined by 51%. In contrast, with mammalian predator control at the Otago Peninsula, the population has seen a 6-10% increase in the 20 years since 1992.

Threats and conservation

A major threat to breeding birds is predation from introduced predators such as cats, ferrets, rats and stoats. Climate-induced fluctuation in the availability of krill, the principal food of the birds during the breeding season, has a major impact on breeding success.

Breeding

Red-billed gulls breed in large, dense colonies on the mainland, but in scattered or solitary concealed situations on the subantarctic islands, probably to help avoid skua predation. They have an extremely long egg-laying period that can extend from mid September to January. They are monogamous, with the sexes sharing approximately equally in nest-building, incubation and provisioning the chicks. Nests are well developed and consist of grass, seaweed or twigs. The clutch size is normally two eggs, but one and three egg clutches sometimes occur. Supernormal clutches up to five eggs can occur in female-female associations. Eggs are ovoid, mainly brownish or greenish-grey with dark brown spots or blotches. Incubation lasts 21-25 days and chicks begin to fly at 35days and continue to be fed for another c. 30 days. At most colonies, especially at the largest, adults and chicks return to the same colony in which they previously bred or were hatched. If successful at a particular site, adults often return the next year to the same portion of the colony. At Lake Rotorua in a mixed colony of red-billed gulls and black-billed gulls interbreeding has been recorded. The hybrids have been fertile and have bred with red-billed gulls.

Behaviour and ecology

At Kaikoura approximately 83% of pairs retain partners from one season to the next. The longest period that a pair remained together was 17 years. Divorce is highest in young birds and in pairs breeding together for the first time, especially if they were unsuccessful the previous season. An important feature of breeding is courtship feeding of the female by the male. Courtship feeding increases in frequency 16 days prior to the laying of the first egg. If the female is being adequately fed by the male, the female is able to remain in the nest territory for much of the day. Like most species of gulls and terns, the red-billed gull has a sex ratio that is biased in favour of females. At Kaikoura females make up 54.9% of the population. As a result, about 7% of the pairings are female-female pairs. These often produce fertile eggs because at least one of the females allows herself to either be force-copulated with by a male paired with another female, or solicits a copulation.

Food

The main food at the largest colonies is the euphausiid Nyctiphanes australis (krill). At Kaikoura during the breeding season adult gulls can sustain themselves on alternative foods such as earthworms, small fish, garbage and kelp flies, but they are dependent upon an abundant and regular supply of the surface-swarming krill for successful breeding. Outside of the breeding season the diet is highly variable. Some still feed at sea, others feed on small invertebrates along the shore and others will feed from human sources such as handouts in towns or cities, offal being discarded from fishing boats and garbage at rubbish dumps.

Websites

http://en.wikipedia.org/wiki/Red-billed_Gull

References

Falla, R.A.; Sibson, R.A.; Turbott, E.G.1966. A field guide to the birds of New Zealand. Collins Auckland.

Given, A.D.; Mills, J.A.; Baker, A.J. 2005. Molecular evidence for recent radiation in Southern Hemisphere masked gulls. Auk 122: 268-279.

Gurr, L. 1967. Interbreeding of Larus novaehollandiae scopulinus and Larus bulleri in the wild in New Zealand. Ibis 109: 552-555.

Gurr, L.; Kinsky, F.C. 1965. The distribution of breeding colonies and status of the red-billed gull in New Zealand and its outlying islands. Notornis 12: 223-240.

Mills, J.A. 1973. The influence of age and pair-bond on the breeding biology of the red-billed gull Larus novaehollandiae scopulinus. Journal of Animal Ecology 42: 147-162.

Mills, J.A. 1979. Factors affecting the egg size of red-billed gulls Larus novaehollandiae scopulinus. Ibis 121: 53–67.

Mills, J.A. 1989. Red-billed gull. In Lifetime reproduction in birds (ed. I. Newton), pp. 387–404. Academic Press, London.

Mills, J.A. 1994. Extra-pair copulations in the red-billed gull: females with high-quality, attentive males resist. Behaviour 128: 41–64.

Mills, J.A.; Yarrall, J.W.; Bradford-Grieve, J.M.; Uddstrom, M.J.; Renwick, J.A. ; Merilä, J. 2008. The impact of climate fluctuation on food availability and reproductive performance of the planktivorous red-billed gull Larus novaehollandiae scopulinus. Journal of Animal Ecology 77: 1129-1142.

Mills, J.A.; Yarrall, J.W.; Mills, D.A. 1996. Causes and consequences of mate fidelity in red-billed gulls. Partnerships in birds. The study of monogamy (ed. J.M. Black), pp 286–304. Oxford University Press, Oxford.

Miskelly, C.M.; Dowding, J.E.; Elliott, G.P.; Hitchmough, R.A.; Powlesland, R.G.; Robertson, H.A.; Sagar, P.M.; Scofield, R.P.; Taylor, G.A. 2008. Conservation status of New Zealand birds, 2008. Notornis 55: 117-135.

Perriman, L.; Lalas, C. 2012. Recent increase in population size of red-billed gulls (Larus novaehollandiae scopulinus) at Otago, southern New Zealand. Notornis 59: 138-147.

Tasker, C.R.; Mills, J.A. 1981. A functional analysis of courtship feeding in the red-billed gull, Larus novaehollandiae scopulinus. Behaviour 77: 221-141.

Recommended citation

Mills, J.A. 2013. Red-billed gull. In Miskelly, C.M. (ed.) New Zealand Birds Online. www.nzbirdsonline.org.nz

Red-billed gull

Breeding season
  • Jul
  • Aug
  • Sep
  • Oct
  • Nov
  • Dec
  • Jan
  • Feb
  • Mar
  • Apr
  • May
  • Jun
Egg laying dates
  • Jul
  • Aug
  • Sep
  • Oct
  • Nov
  • Dec
  • Jan
  • Feb
  • Mar
  • Apr
  • May
  • Jun

Red-billed gull

Social structure
monogamous
Breeding season
  • Jul
  • Aug
  • Sep
  • Oct
  • Nov
  • Dec
  • Jan
  • Feb
  • Mar
  • Apr
  • May
  • Jun
Nest type
ground-level platform
Nest description
Well made nest with a depression.
Nest height (mean)
0.00 m
Maximum number of successful broods
1
Clutch size (mean)
2
Clutch size (min)
1
Clutch size (max)
3
Mean egg dimensions (length)
52.90 mm
Mean egg dimensions (width)
37.70 mm
Egg colour
Mainly brownish-grey with dark brown spots or blotches
Egg laying dates
  • Jul
  • Aug
  • Sep
  • Oct
  • Nov
  • Dec
  • Jan
  • Feb
  • Mar
  • Apr
  • May
  • Jun
Interval between eggs in a clutch
1 days
Incubation behaviour
shared
Incubation length (mean)
24 days
Incubation length (min)
23days
Incubation length (max)
26days
Nestling type
semi-precocial
Nestling period (mean)
About 45 days
Age at independence (mean)
About 55 days
Age at first breeding (typical)
2-6 years
Maximum longevity
30 years
Maximum dispersal
650 km