GREAT BLACK-BACKED GULL (Larus marinus) – (See images below)
DESCRIPTION: The Great black-backed gull is not quite black, but is rather dark grey on its back and wings, whereas the head and neck are white.  The under parts are white. The bill is yellow with a reddish spot near the tip of the lower mandible. The eyes are yellow with a thin red circle around them, and the legs are pink. Juveniles have a mottled brown plumage and a black bill. It takes them four years to reach adult plumage. Sexes are similar. It is the largest member of its family at some 30 inches long (75 cm).
NAME: The English name ‘Gull’ would have its origins in Old Celtic ‘Gullan’ and other languages, including Latin ‘gula’ for throat. As per Choate this would be related to the gull’s ‘indiscriminate’ scavenging habits, its ‘willingness to swallow almost anything’ (think ‘gullible’). The Latin genus name ‘Larus’ means ‘gull’, and the Latin species name ‘marinus’ means ‘marine’.
HABITAT: Along the coasts, rivers, lakes, ponds, etc.
DIET: Like other gulls, great black-backed gulls are scavengers, hence can be found in large numbers around garbage. They feed on fish, and are known to throw shellfish on rocks or roads from the air, in order to break the shell and reach its contents. They also prey on other birds.
NESTING: The nest is a scrape on the ground in a sheltered area. In urban areas the birds can build their nests on roofs. Usually three beige eggs are laid, which are incubated by both parents. They also both feed the young.
DISTRIBUTION: This bird is found in the northern Atlantic regions on each side of the ocean. It migrates south of its breeding range where bodies of water are free of ice in the winter. Some vagrants have been reported on Hawaii. (See note below for information on bird vagrancy.)
ON PEI: The great black-backed gull is a year-round resident on Prince Edward Island, and is very common.

CONSERVATION: This gull species used to be hunted for its feathers for the hat fashion industry. It has made a recovery since and has now increased its population to the point where it is considered a pest in some areas, for example around airports. It is also threatening some vulnerable seabirds and there are steps taken to manage their population on some bird sanctuary islands.
Vagrancy: In biology this means an animal going way outside its normal range. For birds, this can happen when there are storms and they get blown off course. On other times, the bird simply wanders in a different direction than usual. Here’s an article about vagrancy in birds.
GULLS ON HAWAII: Gulls are not long time residents or indigenous to Hawaii. They are continental species and the Hawaiian Islands don’t seem to provide them with the habitat they need. Those birds that do make it however have either flown on their own or got blown off course, or hitched a ride on ships. In either case they don’t stay for long. 
SIMILAR SPECIES: Lesser Black-backed Gull
REFERENCES: (Maritimes Breeding Bird Atlas) (Norwegian Polar Institute)
Protecting Colonial Nesting Birds – Island Nature Trust, PEI (.pdf brochure)

Great black-backed gull, Borden, PEI,  Canada Sept. 2, 2013, © Roberta Palmer
Great black-backed gull, Borden, PEI,
Canada Sept. 2, 2013, © Roberta Palmer
Great black-backed gull with Herring gulls,  PEI, Canada, © Marie Smith
Great black-backed gull with Herring gulls,
PEI, Canada, © Marie Smith