Swallow-tailed Gull

By Archives •  Updated: 07/18/22 •  2 min read

The Swallow-tailed gull (Creagus furcatus) is a nocturnal foraging seabird that breeds mostly in the Galapagos Islands; a few pairs nest on Malpelo Island off Colombia. Nesting pairs feed nearby their nesting islands but when it is not breeding, the swallow-tailed gull travels widely in the Humboldt Current region including as far north as Panama, and south to Peru.

Its habit of nocturnal foraging is unique among gulls. Its diet is squid and fish. Nocturnal foraging might be an adaptation to avoid kleptoparasitism (piracy) by frigate birds.

In order to see while hunting for food at night, the swallow-tailed gull’s eyes are larger in size and volume than those of any other gull. They also possess a tapetum lucidum in the back of the eye that reflects light back through the retina, increasing the amount of light available to the photoreceptor cells.

Also unusual among gulls is the swallow-tailed gull’s single egg clutch. Most gulls and relatives lay 2-3 eggs in a clutch.

Swallow-tailed Gull Calls

A group of Swallow-tailed Gull

Credit: Byron Chin, CC-BY

Calls and displays are quite different from other gulls, most resembling the vocalizations of the black-legged kittiwake and Sabine’s gull.

The loudest and most commonly heard call is an alarm referred to as “rattle-and-whistle”, a gurgling scream made with the head moving side to side. This call is contagious, with other birds joining in without seeing the cause. A loud and rapid kweek, kweek, kweek is the greeting call between mates, made with the head and neck curved forward to the ground.

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 looke at in 2004.

This type of gull was first described by the French naturalist and surgeon Adolphe-Simon Neboux in 1846. Its scientific name is originally derived from the Greek word for gull, “Glaros” and via Latin Larus, “gull” and furca “two-tined fork”.

Sources:

Agreda, ANA and DJ Anerson. 2003. Evolution of single chick broods in the swallow-tailed gull Creagus furcatus. Ibis 145: 53-58.

Hailman, J. 1964. The Galapagos Swallow-tailed Gull is nocturnal. Wilson Bulletin 76: 347-354.

Harris, MP 1970. Breeding ecology of the Swallow-tailed Gull. Auk 87:215-243.

Harrison, P. 1983. Seabirds. Houghton Mifflin, Boston.

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