Overview

Brief Summary

Biology

The black-billed gull is a social and gregarious species, forming large flocks to forage and to breed. They are forced to travel long distances to feed each day as the flock can clear an area of food within a day. They scavenge less than many other gull species, but will follow ploughs to pick up earthworms and insects from the freshly-turned farmland. The birds feed from lakes and rivers as well, selecting small fish and aquatic invertebrates, as well as picking flying insects out of the air above the water (2). Food is spotted during soaring flight, and the gulls will descend on areas such as tussock grassland to eat moths, calling noisily as they do so (3). During the breeding season the black-billed gull returns to the same site it visits every year and pairs begin to build deep depressions of twigs and grass during October. The female lays between one and three eggs on lake edges or in braided rivers, and these are incubated by both the male and female for about 22 days continuously. After hatching, the chicks are fed by their parents until they fledge around 26 days later. The family stays at the breeding site until fledging unless disturbed when they may abandon the nest as soon as the majority of their eggs have hatched, moving on to coastal habitats for the winter. The young are able to breed after two years, but more normally will not pair up until three or four years of age (3).
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Description

Adapted for sustained, soaring flight, the black-billed gull has a compact body with long wings and a fan-shaped tail to help control movement in strong winds. With typical colouration for a gull, the black-billed gull can be distinguished by its black bill, legs, feet and wing tips, against a background of grey on the wings and back and white on the head, neck, breast, underside and tail (2) (3).
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Distribution

Range Description

Larus bulleri is endemic to New Zealand. The majority of the population (78%) breeds in Southland (Taylor 2000), mostly on the Mataura, Oreti, Aparima and Waiau rivers (Powlesland 1998). On the Oreti and Aparima, the number of breeding birds appears to have plummeted by as much as 90% in the last one to two decades (Powlesland 1998, Taylor 2000, McClellan in litt. 2007). Upper Waitaki catchment populations declined between the 1960s and 1990s, with breeding colonies disappearing from six rivers (Maloney 1999). Recent surveys at one minor colony in the Hunter Valley, Otago, showed numbers had dropped from 581 in 1969 to just 12, with the same trend seen in the nearby Makarora catchment area (R. Hitchmough in litt. 2005). Overall, Southland counts estimated a minimum of 57,000 pairs in 1985-1986 (Taylor 2000), declining by c.40% to 33,500 pairs in 1996-1997 (Powlesland 1998). Its numbers and range continue to increase in the North Island, but these colonies are small and the increase does not offset the South Island declines (R. Hitchmough in litt. 2005). The most complete nationwide census was carried out in 1996-1997 (G. A. Taylor per R. Coumbe in litt. 2000), and counted 48,000 nests (Powlesland 1998). Some birds remain at colonies throughout the year, others move from inland breeding sites to the coasts (Higgins and Davies 1996).

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Range

South I. (New Zealand); winters to North I..
  • Clements, J. F., T. S. Schulenberg, M. J. Iliff, D. Roberson, T. A. Fredericks, B. L. Sullivan, and C. L. Wood. 2014. The eBird/Clements checklist of birds of the world: Version 6.9. Downloaded from http://www.birds.cornell.edu/clementschecklist/download/

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Range

Endemic to New Zealand, the black-billed gull is found in the north of South Island and south of North Island and on nearby Stewart and Snares Islands (2) (3).
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Ecology

Habitat

Habitat and Ecology

Habitat and Ecology
In the South Island, it breeds mainly on braided river systems (Higgins and Davies 1996, Taylor 2000). In the North Island, it uses sand-spits, shellbanks, lake margins and riverflats (Taylor 2000). It often roosts and feeds on farmland, and scavenges in urban areas where refuse is available (Higgins and Davies 1996). It has a varied diet of terrestrial, freshwater and marine invertebrates, fish and shellfish (Higgins and Davies 1996, Heather and Robertson 1997). Breeding can begin after two years (Heather and Robertson 1997), but many individuals do not start until six years old, and adults may live over 30 years (R. Hitchmough in litt. 2005).


Systems
  • Terrestrial
  • Freshwater
  • Marine
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This species is found on the small islands of braided rivers, the margins of lakes, in parks, and on wet lawns, sheep pastures and ploughed fields. It is found both in coastal regions and further inland, typically moving closer to either the coast or to towns during the winter, after breeding inland (2) (3) (4) (5).
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Molecular Biology and Genetics

Molecular Biology

Statistics of barcoding coverage: Larus bulleri

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 0
Specimens with Barcodes: 7
Species With Barcodes: 1
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Conservation

Conservation Status

IUCN Red List Assessment


Red List Category
EN
Endangered

Red List Criteria
A2ce+3ce+4ce

Version
3.1

Year Assessed
2015

Assessor/s
BirdLife International

Reviewer/s
Butchart, S.

Contributor/s
Hitchmough, R., McClellan, R. & Taylor, G.

Justification
Surveys indicate that this species may have undergone a very rapid decline over three generations (32 years). It is therefore listed as Endangered.


History
  • 2012
    Endangered (EN)
  • Endangered (EN)
  • Endangered (EN)
  • Endangered (EN)
  • Vulnerable (VU)
  • Vulnerable (VU)
  • Lower Risk/least concern (LR/lc)
  • Lower Risk/least concern (LR/lc)