Swallow-tailed gull

Appearance

The swallow-tailed gull has no structural or plumage differences between the male and female. In the breeding season, the adult has a black plumaged head and a bright red fleshy rim around each eye. Outside the breeding season, the head is white and the eye rim becomes black. It has a grayish upper breast, gray mantle, and black wingtips. The mostly black bill has a contrasting white tip.

Distribution

The swallow-tailed gull is a near-endemic breeding bird of the Galápagos Islands, although a few pairs nest on Malpelo Island off the coast of Colombia. When not breeding, it is totally pelagic, flying and hunting over the open oceans, and migrating eastward to the coasts of Ecuador and Peru.

Status

Population trends have not been estimated, but it is not thought to be threatened. The population was estimated to be about 35,000 individuals when it was last considered in 2004.

Habitat

The swallow-tailed gull is a near-endemic breeding bird of the Galápagos Islands, although a few pairs nest on Malpelo Island off the coast of Colombia. When not breeding, it is totally pelagic, flying and hunting over the open oceans, and migrating eastward to the coasts of Ecuador and Peru.

Reproduction

The swallow-tailed gull breeds from about 5 years old, with pairs frequently staying together from year to year. Most breed throughout the year in mixed colonies on the cliffs of the Galápagos Islands sometimes on flat areas, and food for the young is hunted from the seas near to the nesting colonies. The nest is made on a small platform on a cliff, usually less than 10 m above sea level, by covering the rocky ground with small pieces of lava, white coral, and sea urchin spines, which prevent the egg from rolling. Nesting birds tend to face the cliff, a habit common among exclusively cliff nesting gulls, such as the black-legged kittiwake. The female usually lays one speckled egg per breeding attempt. They are asynchronous breeders, and follow a nine-month cycle, or less if an egg or chick is unsuccessful. The egg is generally incubated for 31–34 days. A chick takes its first flight at about 60–70 days old, and is fed by the adults until about 90 days, when it leaves the land, possibly with the adults, to live over the open seas.

Food

The swallow-tailed gull is unique among the gulls in feeding exclusively nocturnally, mostly on fish and squid which rise to the surface at night to feed on plankton. It leaves the colony as a flock at dusk, with a great deal of screaming and display.