LC
Great Black-backed Gull Larus marinus



Justification

Justification of Red List Category
This species has an extremely large range, and hence does not approach the thresholds for Vulnerable under the range size criterion (Extent of Occurrence <20,000 km2 combined with a declining or fluctuating range size, habitat extent/quality, or population size and a small number of locations or severe fragmentation). Despite the fact that the population trend appears to be decreasing, the decline is not believed to be sufficiently rapid to approach the threshold for Vulnerable under the population trend criterion (>30% decline over ten years of three generations). The population size is very large, and hence does not approach the thresholds for Vulnerable under the population size criterion (<10,000 mature individuals with a continuing decline estimated to be >10% in ten years or three generations, or with a specified population structure). For these reasons the species is evaluated as Least Concern.

Population justification
The European population is estimated at 118,000-133,000 pairs, which equates to 237,000-266,000 mature individuals or 360,000-400,000 individuals (BirdLife International 2015). Combining the European population estimate with that for the north-west Atlantic population in Wetlands International (2015) gives a global estimate of 690,000-940,000 individuals. It is therefore placed in the band 500,000-999,999 individuals.

Trend justification
Historically, the species underwent a marked population increase and range expansion southwards between the 1930s and 1975, as well as spreading north to Spitsbergen. In the Nearctic, the breeding range has also extended southwards since the mid-20th century; it first bred in Maine in 1928, Massachusetts in 1931, New York in 1940, the Great Lakes in 1954, and New Jersey in 1966. In New England the population increased from 30 pairs in 1930 to 12,400 in 1972 (Burger et al. 2018). Over the last 50 years, the population in North America has been decreasing at about 29.7% over three generations (36 years), but the estimate yields large uncertainties (data from Christmas Bird Count, T. Meehan in litt. 2018). Also in some northern European countries, the species is in decline; however, these declines are relatively short-term adjustments. Recent trend estimates for the UK indicate that over the past three generations, overall declines are of a far smaller magnitude than between 2000 and 2012 (JNCC 2018). These short-term declines do not appear to be continuing (JNCC 2018). Similarly, while the trend in Sweden between 2001 and 2011 was estimated as a decline of between 20-50%, the long term (1980-2011) trend was stable: the population increased to the 1990s, then stabilised prior to the decline. Using the trend that most closely matches the three generation length,  reduces the estimate of the current rate of decline to 23.6%. Recent declines observed in offshore populations on the North Sea and Baltic Sea are not reflected in analogous trends at the breeding sites and may indicate a shift in the distribution or habitat use (Markones et al. 2015, N. Markones in litt. 2018).

Distribution and population

The species has a very large, trans-Atlantic distribution, being found from the Great Lakes, U.S.A. and the east coast of U.S.A. and Canada, coastal Greenland, Iceland, Faroe Islands, Svalbard, U.K., Republic of Ireland, the west coast of mainland Europe, Scandinavia, Estonia and coastal European Russia. Individuals breeding in harsher environments will migrate south, wintering on northern coasts of Europe from the Baltic Sea to southern Portugal, and down North America as far south as the Caribbean (del Hoyo et al. 1996).

Ecology

Behaviour The migratory movements of this species vary throughout its range, with high Arctic breeders migrating south for the winter but southern breeders only dispersing short distances (del Hoyo et al. 1996). The breeding season starts from early-April or mid-May with the species nesting in solitary pairs amidst colonies of other species or in small mixed-species colonies (del Hoyo et al. 1996) of up to 50-100 individuals (Richards 1990), e.g. with Herring Gull Larus argentatus (del Hoyo et al. 1996) in favourable locations (Richards 1990). The autumn migration occurs between July and November (peaking October-November) and the return migration to the breeding grounds occurs between March and April (Olsen and Larsson 2003). Outside of the breeding season the species is largely gregarious (Olsen and Larsson 2003). Habitat The species inhabits rocky or sandy coasts, estuaries and inshore and offshore waters, breeding on vegetated islands, dunes, flat-topped stacks, rocky shores (del Hoyo et al. 1996), flat beaches (Snow and Perrins 1998) and islands in saltmarsh (del Hoyo et al. 1996). The species may also breed on undisturbed inland sites including islets in large freshwater lakes and rivers (Snow and Perrins 1998), fields and open moorland (del Hoyo et al. 1996). Diet The species is omnivorous and opportunistic, its diet consisting of fish, adult and young birds, birds eggs, mammals (rabbits, lemmings, rats and mice), insects, marine invertebrates (molluscs), carrion and refuse (del Hoyo et al. 1996). Breeding site The nest is a shallow cup constructed from grass, moss and seaweed and is positioned on sand, grass or bare rock substrates on vegetated islands, rocky ridges and outcrops, dunes (del Hoyo et al. 1996), flat beaches (Snow and Perrins 1998) and islands in saltmarsh among scrub (del Hoyo et al. 1996). The species may also nest in undisturbed inland sites such as islets in large freshwater lakes and rivers (Snow and Perrins 1998), fields and open moorland (del Hoyo et al. 1996). Management information The breeding densities of this species in the Baltic Sea were unaffected by the removal of the introduced nest predator American Mink Neovison vison from small offshore breeding islands (Nordstrom et al. 2003). The species is considered to be a threat to other bird species due to its predatory and opportunistic diet (del Hoyo et al. 1996).

Threats

Continuing reductions in the quantities of available discards in the North Atlantic are believed to be driving the observed decline in eastern Atlantic populations in recent years (Burger et al. 2018). The species is hunted for sport in Denmark (Bregnballe et al. 2006). Within its European range it is vulnerable to collision with offshore wind farms (Bradbury et al. 2014) and to being caught as bycatch in fishing gear, including longlines, trawls and gill-nets (Anderson et al. 2011, Žydelis et al. 2013). It is vulnerable to coastal oil spills and other types of surface water pollution.

Conservation actions

Conservation Actions Underway
The following information refers to the species's European range only: The species is covered under the African Eurasian Waterbird Agreement. In the EU it is listed under Annex II of the Birds Directive. There are 54 Important Bird Areas within Europe for this species. Within the EU there are 111 Special Protection Areas which include this species. 

Conservation Actions Proposed
The following information refers to the species's European range only: Continued monitoring of numbers hunted. On board observer programmes on fishing vessels to monitor bycatch rates, and appropriate mitigation measures implemented where necessary.

Acknowledgements

Text account compilers
Westrip, J., Butchart, S., Ekstrom, J., Hermes, C., Malpas, L., Calvert, R., Martin, R., Ashpole, J, Stuart, A.

Contributors
Markones, N.


Recommended citation
BirdLife International (2020) Species factsheet: Larus marinus. Downloaded from http://www.birdlife.org on 28/11/2020. Recommended citation for factsheets for more than one species: BirdLife International (2020) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 28/11/2020.