The black-billed gull (''Chroicocephalus bulleri''), Buller's gull, or tarāpuka ( Māori) is a

Near Threatened A near-threatened species is a species which has been categorized as "Near Threatened" (NT) by the International Union for Conservation of Nature as that may be vulnerable to endangerment in the near future, but it does not currently qualify f ...

species of gull in the family

Laridae Laridae is a family of seabirds in the order Charadriiformes that includes the gulls, terns, skimmers and kittiwakes. It includes around 100 species arranged into 22 genera. They are an adaptable group of mostly aerial birds found worldwide. ...

. This gull is found only in

New Zealand New Zealand ( mi, Aotearoa ) is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and over 700 smaller islands. It is the sixth-largest island count ...

, its ancestors having arrived from Australia around 250,000 years ago.

Taxonomy

Originally named ''Gavia pomare'' in 1855 by

Carl Friedrich Bruch Carl Friedrich Bruch (March 11, 1789 – December 21, 1857) was a German ornithologist. He was the younger brother of bryologist Philipp Bruch (1781–1847).Sir Walter Lawry Buller because it was already being used for another species. He then took up

Prince Napoléon Bonaparte A prince is a male ruler (ranked below a king, grand prince, and grand duke) or a male member of a monarch's or former monarch's family. ''Prince'' is also a title of nobility (often highest), often hereditary, in some European states. Th ...

’s "playful" genus name ''Bruchigavia'' (literally, "Bruch's seabird") as a provisional name for New Zealand gulls. But because Buller's proposed species name ''melanoryncha'' (literally, "black-billed") had already been given to another gull species, Frederick Hutton suggested the name ''bulleri'', in honor of Buller, in 1871. Buller accepted the offer and followed others in adopting the "larger and better-defined genus" of ''

Larus ''Larus'' is a large genus of gulls with worldwide distribution (by far the greatest species diversity is in the Northern Hemisphere). Many of its species are abundant and well-known birds in their ranges. Until about 2005–2007, most gulls ...

''. The alternative common name Buller's gull also retains the connection to Buller. The species is now considered to belong within the genus ''

Chroicocephalus ''Chroicocephalus'' is a genus of medium to relatively small gulls which were included in the genus '' Larus'' until recently. Some authorities also include the Saunders's gull in ''Chroicocephalus''. The genus name '' Chroicocephalus'' is from ...

''. The

holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of sever ...

is in the collection of the Museum of New Zealand Te Papa Tongarewa.

Description

A healthy adult black-billed gull is typically 35–38 cm long, with a wingspan of 81–96 cm, and a weight of around 230g. The head, body, and parts of the wings are white, with silvery grey on the saddle and wings, as well as black edging on the wings. The gull also undergoes some seasonal color change. While typically black from February to June, the

orbital ring An orbital ring is a concept of an artificial ring placed around a body and set rotating at such a rate that the apparent centrifugal force is large enough to counteract the force of gravity. For the Earth, the required speed is on the order of 1 ...

is orange-red, red, or dark red the rest of the year. The legs, too, change from black to dark red and even bright red as the breeding season progresses, "possibly stimulated by presence of begging chicks and juveniles." Observations suggest the gull is sexually dimorphic, but there is a lack of published data to support this. There is likewise a lack of data in regard to geographical variation. Easily mistaken for the red-billed gull, the black-billed gull is distinguished by its black bill and is described as having a “more delicate appearance,” a “more buoyant and graceful” flight, and being “generally less noisy,” despite having a similar call. F1 and F2 hybrids between the two gulls have been observed, both hybrids exhibiting dark red bills.

Behaviour

Colonies are formed around the first pair that begins nesting. Where more than one pair forms the initial nest, clustering around these sites takes place within the colony. Colonies are frequently tightly packed, with “Gulls little more than pecking distance from each other and nests often touch, leaving little room for taking off and landing.” Males may display aggressive behavior towards others in an “ill-defined area” for a few minutes before leaving the area and forgetting it. Nonetheless, not all male aggression is linked to defending a particular area, and some pairs without chicks will show aggression towards those with chicks. Fights are rarely prolonged, usually consisting of a single attack by the aggressor, employing the bill for pecking, the wings for beating, and the legs for scratching. The target typically retreats right away. Adults roost at the breeding colony or feeding sites, though the latter is more common.

Distribution and habitat

The black-billed gull is

endemic Endemism is the state of a species being found in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also found else ...

to New Zealand. Up to 78% of the total population is estimated to be living in the

Southland Southland may refer to: Places Canada * Dunbar–Southlands, Vancouver, British Columbia New Zealand * Southland Region, a region of New Zealand * Southland County, a former New Zealand county * Southland District, part of the wider Southland Re ...

region, on the southern end of the South Island. In breeding season the gull is found on major rivers, especially braided rivers, lakes, and farmland. It generally prefers estuaries and coastal areas outside of the breeding season, though some can be found at breeding sites all year round. The gull is also attracted to urban areas, and "anywhere refuse of scraps available", such as rubbish dumps and

freezing works A slaughterhouse, also called abattoir (), is a facility where animals are slaughtered to provide food. Slaughterhouses supply meat, which then becomes the responsibility of a packaging facility. Slaughterhouses that produce meat that is no ...

. In 2019 some gulls established a colony of around 300 birds in

Christchurch Central City Christchurch Central City or Christchurch City Centre is the geographical centre and the heart of Christchurch, New Zealand. It is defined as the area within the Four Avenues (Bealey Avenue, Fitzgerald Avenue, Moorhouse Avenue and Deans Avenue ...

. The species has been sighted occasionally on Stewart Island and

The Snares The Snares Islands / Tini Heke, known colloquially as The Snares, is a group of uninhabited islands lying about 200 km south of New Zealand's South Island and to the south-southwest of Stewart Island / Rakiura. The Snares consist of the ma ...

, as well as at altitudes of up to 1700 MASL on the mainland. Various colonies also live on the North Island, though it was formerly only a "visitor", the first recorded breeding taking place at

Lake Rotorua Lake Rotorua ( mi, Te Rotorua nui ā Kahumatamomoe) is the second largest lake in the North Island of New Zealand by surface area, and covers 79.8 km2. With a mean depth of only 10 metres it is considerably smaller than nearby Lake Tarawera ...

in 1932. Some South Island birds cross the

Cook Strait Cook Strait ( mi, Te Moana-o-Raukawa) separates the North and South Islands of New Zealand. The strait connects the Tasman Sea on the northwest with the South Pacific Ocean on the southeast. It is wide at its narrowest point,McLintock, A ...

after breeding season to winter in the North Island.

Important Bird Areas

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

Canterbury Canterbury (, ) is a cathedral city and UNESCO World Heritage Site, situated in the heart of the City of Canterbury local government district of Kent, England. It lies on the River Stour. The Archbishop of Canterbury is the primate of ...

region *

Ashburton River / Hakatere The Ashburton River / Hakatere is a river in the Canterbury region of New Zealand, flowing across Mid Canterbury from the Southern Alps to the Pacific Ocean. The official name of the river was amended to become a dual name by the Ngāi Tahu Clai ...

* Ōpihi River * Opuha Dam * Orari River *

Rakaia River The Rakaia River is in the Canterbury Plains in New Zealand's South Island. The Rakaia River is one of the largest braided rivers in New Zealand. The Rakaia River has a mean flow of and a mean annual seven-day low flow of . In the 1850s, Eu ...

;

region *

Aparima River The Aparima River, earlier known as Jacob's River, is one of the southward-flowing braided rivers of Southland, New Zealand. Description The Aparima has its headwaters in the Takitimu Mountains, south of Lake Te Anau, and flows south for before ...

* Eyre Creek * Mararoa River *

Mataura River The Mataura River is in the Southland Region of the South Island of New Zealand. It is long. Description The river's headwaters are located in the Eyre Mountains to the south of Lake Wakatipu. From there it flows southeast towards Gore, whe ...

Ōreti River The Ōreti River (formerly the Oreti River) is one of the main rivers of Southland, New Zealand, and is long. The river has been identified as an Important Bird Area by BirdLife International because, for much of its length, it supports bree ...

* Whitestone River

Status

In regard to Southland colonies, Rachel McClellan notes that “surveys in the 1970s indicated a population of about 140,000 breeding birds, whereas recent counts gave estimates of only 15-40,000 breeding birds”. Nonetheless, different counting methods and the various limitations of these methods mean that “estimates must be treated with caution”. This suggests a 6% decline in population every year across thirty years, equivalent to up to 83.6% over the whole period, or 50% if the data are taken conservatively. Higher population sizes in the 1950s and 1960s were potentially the result of increased agricultural activity, but the correlation is tenuous. Populations at this time were of legendary proportions, with anecdotes telling of farmers who “were forced to wear raincoats so as not to be coated in droppings". Due to "very rapid decline over three generations" the IUCN has rated the species as

. The gull had earlier received a Least Concern rating in 1994, and a Vulnerable rating in 2000. The

New Zealand Department of Conservation The Department of Conservation (DOC; Māori: ''Te Papa Atawhai'') is the public service department of New Zealand charged with the conservation of New Zealand's natural and historical heritage. An advisory body, the New Zealand Conservation Au ...

listed the gull as Nationally Critical in 2016. It has been referred to in other publications as “critically endangered”, and James Westrip proposed in August 2018 that the gull's status be uplisted to Critically Endangered in the next BirdLife International Red List report, though it was eventually downlisted in 2020. Bill Morris calls the bird “the world’s rarest gull”.

Threats

In her study of Southland colonies of black-billed gulls, Rachel McClellan found that eighty per cent of observed chick deaths resulted from predation. Introduced mammals, namely ferrets, stoats, cats, and hedgehogs, constitute the “primary factor influencing productivity,” that is, nest success, in the colonies. Chick predation from the indigenous black-backed gull (''Larus dominicanus'') also threatens the black-billed gull population. While “the species is relatively tolerant of human disturbance,” having potentially benefitted from increasing land conversion for agricultural use since the arrival of Europeans, human activity has also had a negative impact on population size. Largescale shootings of black-billed gulls, such as a 2009 “massacre” of around 200 birds in North Canterbury, are particularly detrimental to the species’ future. A similar event was reported in December 2018, while another article tells of a gull being discovered with an arrow in it. The birds have also been targeted by people in vehicles who “occasionally plough through colonies”. Morris suggests such actions in part result from confusion with the more common and disliked red-billed gull (''Chroicocephalus novaehollandiae scopulinus''), which is nonetheless also endangered in New Zealand. Although no studies have been conducted in this area, previous

DDT Dichlorodiphenyltrichloroethane, commonly known as DDT, is a colorless, tasteless, and almost odorless crystalline chemical compound, an organochloride. Originally developed as an insecticide, it became infamous for its environmental impacts. ...

usage on farms may affect the breeding success of black-billed gulls and herbicides that remain in use could have consequences that are yet unknown. McClellan suggests that climate change could have a positive impact on black-billed gull populations, such as in encouraging earlier or extended breeding seasons, but also a negative impact in increasing food availability, which would result in “poor synchrony”. Nesting on river islands, chicks are also vulnerable to flooding. In a January 2018 flood, a single colony lost up to 2500 chicks. Another colony is thought to have lost around 2200 eggs in a flood in November the same year. In October 2019, Mike Turner responded to a proposal for commercial rafting along the

, citing concerns for the welfare of black-billed gulls.

Conservation efforts

In October 2018, the Department of Conservation began a trial cull of black-backed gulls along the Hurunui River to control predation of black-billed gull chicks and other threatened bird species. In August 2019, after a successful trial, the Department announced a five-year programme extending to the Waiau Uwha River that aims to reduce the black-backed gull population in the areas by at least eighty per cent. The black-billed gull placed 30th, with 441 votes, in Forest & Bird's 2018

Bird of the Year ''Bird of the Year/Te Manu Rongonui o Te Tau'' is an annual election-based competition run by Forest & Bird to elect a "Bird of the Year" in New Zealand. It draws support from well-known personalities including politicians, artists, actors, and ...

competition.

Gallery

References

External links

Further images and videos on arkive.org.
{{Taxonbar, from=Q1270731 black-billed gull Endemic birds of New Zealand black-billed gull Taxonomy articles created by Polbot Taxobox binomials not recognized by IUCN Taxa named by Frederick Hutton (scientist)