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..

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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
2012

Assessor/s
BirdLife International

Reviewer/s
Butchart, S. & Symes, A.

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.

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Status

The black-billed gull is classified as Endangered (EN) on the IUCN Red List 2006 (1).
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Population

Population
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), thus the number of mature individuals is estimated to be 96,000; however, more up-to-date survey data are required.


Population Trend
Decreasing
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Threats

Major Threats
Brown rats Rattus norvegicus take eggs and chicks in the North Island. Remote video cameras have shown that mustelids Mustela spp. and feral cats are major predators on South Island colonies, often taking hundreds of chicks in a season (Biswell 2006). Hedgehogs may also take eggs. The recreational use of riverbeds and coastal areas is increasing, causing greater disturbance of nesting colonies (Taylor 2000). River modification (including hydroelectric development, and water and gravel extraction) also has a significant impact. The spread of weeds is a major threat, reducing suitable nesting habitat on riverbeds (Maloney 1999, Taylor 2000).

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Despite a substantial decline on South Island over the past ten to twenty years, the black-billed gull remains more common on South Island than North Island, where it has actually expanded its range since the 1970s. It is hoped that its overall declining trend has reversed recently, partly due to a change in agricultural practices that has seen more insects and worms being revealed by ploughing. The black-billed gull has developed a habit of following ploughs and aiding farmers by picking out insect pests. However, the breeding habitat of the bird continues to decline in size. This reduction in habitat is the cause of the drop in gull numbers over the last 30 years as land is increasingly turned over to agriculture. Additionally, breeding habitat is currently threatened by the spread of exotic lupins which clog the waterways (2) (5).
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Management

Conservation Actions

Conservation Actions
Conservation Actions Underway
Studies of breeding biology, movements and dispersal are being undertaken. Localised and nationwide counts are on-going. Habitat restoration and protection in the MacKenzie Basin is undertaken as part of Project River Recovery, including predator research and a public awareness campaign (Taylor 2000).

Conservation Actions Proposed
Monitor key breeding populations. Initiate nest protection and trapping of introduced predators at key colonies. Initiate riverbed weed control if nesting habitat continues to be lost. Assess the possible impacts of further hydroelectric dam projects, and gravel and water extraction proposals (Taylor 2000).

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Conservation

The New Zealand Government has launched the New Zealand Biodiversity Strategy to respond to its obligations under the Convention on Biological Diversity. This includes management of wetland habitats by protecting them from development, as well as by planting appropriate plant species in areas recovering from disturbance in order to stabilise the soil and reduce fertiliser run-off that can encourage the growth of exotic species, such as lupins, at the expense of native species. The water level must be maintained and a water care code has been established to ensure that users of wetland habitats are able to act responsibly (6).
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Wikipedia

Black-billed Gull

The black-billed gull (Chroicocephalus bulleri), also known as Buller's gull, is a species of gull in the Laridae family. It is found only in New Zealand.

Taxonomy[edit]

As is the case with many gulls, it has traditionally been placed in the genus Larus, but is now considered to belong within the genus Chroicocephalus. The holotype is in the collection of the Museum of New Zealand Te Papa Tongarewa.[2]

Description[edit]

The black-billed gull is a lightly coloured gull with a small amount of black on its wingtips. It has a long, thin, black bill with a bright red interior, and reddish black feet and white eyes. The juvenile has a flesh coloured bill with a dark tip and dark brown eyes. As juvenile red-billed gulls display similarly dark bills and feet they may be confused with this species.[3]

Distribution and habitat[edit]

Adult at Lake Taupo

The black-billed gull is endemic to New Zealand. Its natural habitats are rivers, freshwater lakes, freshwater marshes, sandy shores, pastureland, and urban areas. It is threatened by habitat loss. About 78% of the population breeds in the Southland Region on the southern end of South Island, New Zealand, especially beside the Mataura, the Oreti, the Aparima and Waiau Rivers. On the North Island, breeding sites are typically sand-spits, shell banks, lake margins and river flats. It feeds on fish, terrestrial, freshwater and marine invertebrates and visits farmland and refuse tips.[3]

Status[edit]

The black-billed gull has shown a marked decline in numbers since about 1980. A census in 1996 showed 48,000 nests which would equate to about 96,000 mature individuals. The bird faces threats from various predators that eat eggs and chicks. These include brown rats, weasels, hedgehogs and feral cats. Nesting colonies are disturbed by people and river modification through dredging or abstraction of gravel and water also impact on them. For these reasons, the IUCN has rated the species as being "Endangered".[3]

Important Bird Areas[edit]

Sites identified by BirdLife International as being important for black-billed gull conservation are:[3]

References[edit]

  1. ^ http://www.doc.govt.nz/Documents/science-and-technical/nztcs1entire.pdf
  2. ^ "Larus bulleri; holotype". Collections Online. Museum of New Zealand Te Papa Tongarewa. Retrieved 17 July 2010. 
  3. ^ a b c d "Black-billed Gull factsheet". BirdLife data zone: Important Bird Areas. BirdLife International. 2012. Retrieved 2012-11-15. 
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