Great Black-backed Gull (Larus marinus)
Nesting great black-backed gulls defend their territories vigorously against other birds, and attract the attention of potential predators by flying in groups above them. These gulls can not only judge the level of threat from a particular predator, but can also remember their assessment if the same predator returns later.
This is the biggest of the Canadian gulls, measuring 70-78 cm in length- as large as a goose. It is unmistakable, with a black back and wings, and plain white underparts. It has pink legs and a yellow bill with a red spot near its tip. Juvenile gulls, from 1-3 years old, are brownish-grey, with a light rump and a dark band on the tail. In flight, great black-backed gulls are slow and soar frequently. This gull has a low, guttural voice, and its typical call is a deep keeow.
The great black-backed gull breeds on the east coast of North America, from northern Labrador to North Carolina. In winter, its range shifts south, spanning the coastline from southern Labrador to the southern tip of Florida, and extending inland to the lower Great Lakes.
The great black-backed gull is monogamous and usually colonial, with pair-bonds occasionally lasting for several breeding seasons. It nests on rocky shorelines, islands, and grassy areas near water. Great black-backed gulls often share nesting sites with herring gulls, double-crested cormorants, and various species of terns. The nest is constructed by both the male and female, and consists of a mound of seaweed, algae, moss, or rubbish, lined with grass. Two or three olive, brown-marked eggs are laid, and are incubated by both parents for 26 to 29 days. The young are semiprecocial, and are cared for by both parents until fledging, at 49 to 56 days of age.
The great black-backed gull is aggressive, and a notorious nest robber, pirate, and scavenger. It rarely catches its own food. When feeding, great black-backed gulls associate with other gulls, in particular, herring gulls and ring-billed gulls. They eat a wide variety of foods, including smaller birds, eggs, and fish, which are often stolen from other gulls. They also eat small mammals, carrion, and grains.