Black-legged Kittiwake

The black-legged kittiwake (Rissa tridactyla) is a member of the gull family Laridae, characterized by its white head and body, grey back, and grey wings tipped with solid black. Adults typically measure 37–41 cm in length, with a wingspan of 91–105 cm, and weigh between 305–525 g. Notably, this species has black legs and a yellow bill, with some individuals displaying pinky-grey to reddish legs. The species is distinguished by its three-toed feet, with the hind toe being greatly reduced or absent.

Identification Tips

Adults in breeding plumage exhibit a clean white head and body, with a grey back and wings, and black wingtips. The bill is bright yellow, and the legs are black. In winter, they develop a dark grey smudge behind the eye and a grey collar on the hind-neck, with the bill turning dusky-olive. Juveniles can be recognized by a black 'W' across the wings, a black hind-neck collar, a black tail band, and a solid black bill.

Habitat

The black-legged kittiwake is a coastal bird, favoring the arctic to subarctic regions. It is most commonly found nesting on sheer sea cliffs during the breeding season and spends the rest of the year at sea.

Distribution

This species inhabits the northern coasts of the Atlantic, from Canada to Greenland, and on the Pacific from Alaska to Siberia. Its wintering range extends south to the St-Lawrence, southern coast of New Jersey, China, the Sargasso Sea, and off the coast of West Africa.

Behaviour

Kittiwakes are highly pelagic outside the breeding season, spending most of their time on the wing and rarely coming inland. They are colonial nesters, forming monogamous pairs and sharing responsibilities in nest building, incubation, and chick-rearing.

Song & Calls

The black-legged kittiwake is named for its distinctive call, a shrill 'kittee-wa-aaake, kitte-wa-aaake'. They have a variety of vocalizations, including greeting calls between mates, alarm calls, and begging calls from females to males.

Breeding

Breeding occurs in large colonies on cliffs, with both sexes participating in nest construction. The breeding season typically runs from May to September. They lay one to three sub-elliptical eggs, which vary in color and are incubated for about 27 days. Chicks are semi-precocial and exhibit siblicide, with the first-born sometimes killing its sibling to reduce competition for food.

Similar Species

The red-legged kittiwake is the closest relative and can be distinguished by its red legs and slightly smaller head with a shorter bill. Juvenile black-legged kittiwakes can be confused with Bonaparte's gull juveniles but have more black on the primaries and a different wing pattern.

Diet and Feeding

Kittiwakes primarily feed on fish, supplemented by invertebrates such as copepods and squids. They forage at the sea's surface, catching prey in flight or while sitting on the water. Their diet varies with location, from Pacific capelin and herring in Alaska to sandeels in the UK.

Conservation status

The black-legged kittiwake is currently classified as Vulnerable by the IUCN Red List. The global population has declined by about 40% over three generations, with threats including fisheries and global warming affecting their food sources.

Subspecies

There are two subspecies: R. t. tridactyla in the North Atlantic, with a very small or absent hind toe, and R. t. pollicaris in the North Pacific, which has a normally developed hind toe.