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 (e.g. rabbits, lemmings, rats and mice), insects, marine invertebrates (e.g. 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).