Great Black-backed Gull

Distribution, movements and phenology

The Great Black-legged Gull breeds from the far north-west of Russia, including Scandinavia and the Baltic Sea coast, the United Kingdom, Ireland and north-west France, through Iceland and southern Greenland, to the Atlantic coasts of Canada and the northern United States (del Hoyo et al. 1992). In winter, its northernmost populations migrate to milder latitudes, with Portugal marking the southern limit of its European range (del Hoyo et al. 1992). In Mainland Portugal, it is found along the entire coast, mainly frequenting the northern half of the country, as far as the Sado estuary (Catry et al. 2010a). The species occurs from mid-September onwards, with the majority of birds observed during the wintering period (Ornithological Reports; Catry et al. 2010a). There are also records of non-breeding individuals during the spring and summer months (Leitão et al. 1998; Catry et al. 2010a). At sea, it appears to be more common in autumn and spring. Recaptures of ringed individuals indicate that the birds arriving in Portugal generally originate from European colonies, such as those in Ireland or northern France (Harris 1962; Bernis 1967), but a bird from Canada has also been observed in the north of the country (Catry et al. 2010a). The species is a regular visitor to all the islands of the Azores, in small numbers and mainly during the non-breeding season (Birding Azores 2014).

Abundance and population trends

The species is very scarce in Portugal, and its abundance may depend on the severity of winters in northern Europe. Sightings of this gull have been increasing on the Mainland and in the Azores (Ornithological Reports), possibly due to the greater number of observers. Globally, the trend for the species has been one of slight increase, with American populations remaining stable (Delany & Scott 2006). However, in some key European populations, such as those in the United Kingdom, a progressive decline has been recorded, particularly in recent years (Taylor & Tipling 2014).

Ecology and habitat

Outside the breeding season, this gull is frequently observed in mixed flocks with the Lesser Black-backed Gull, which sometimes makes it difficult to detect. It is usually seen resting on sandy beaches, rocky coastlines or in harbour areas, and sometimes occurs offshore on the continental shelf (Catry et al. 2010a). The Great Black-legged Gull is an opportunistic species and therefore has a varied diet. In breeding areas, this may include small fish, eggs, juvenile or adult birds, small mammals, insects, or even carrion and organic waste (del Hoyo et al. 1992).

Threats and conservation

No specific threats to this gull are known in Portuguese waters. As a species with opportunistic habits, it may be locally affected by the ban on discards from fishing vessels (Taylor & Tipling 2014). Its recent decline in the United Kingdom has led to the cessation of population control measures for this species, such as culling and the destruction of nests under licence (Taylor & Tipling 2014). In Denmark, it is considered a game species (Bregnballe et al. 2006).

Autor

Meirinho et al. 2014