Last updated on April 16, 2014 at 16:55 EDT

Swallow-tailed Gull, Creagrus furcatus

The Swallow-tailed Gull (Creagrus furcatus) is a species of seabird of the gull family. It is found in the equatorial seas where it spends most of its time hunting on the open ocean. Its main breeding grounds is on the cliffs of the larger Galápagos Islands, and on some of the smaller islands. It is typically found along the eastern islands where the water is warmer. It is also found in smaller numbers on Malpelo Island off the coast of Colombia. It is the only fully nocturnal seabird in the world. When not breeding, it is totally pelagic (living on the open seas). It migrates east toward the coasts of Ecuador and Peru.

The adult Swallow-tailed Gull has no differences in plumage between sexes. During the breeding season, the adult has a black head, with bright red fleshy rims around each eye. During the rest of the year, the head is white and the eye rim is black. The upper breast is grayish, the mantle is gray, and the wingtips are black. The black bill has a white tip. The call is referred to as a “rattle-and-whistle”, and is a gurgling scream that the bird makes while moving its head from side to side. Other birds will join in for no reason. The greeting call is a rapid kweek, kweek, kweek sound between males.

This species feeds exclusively at night. It preys on squid and small fish that come to the surface at night to feed. Its eyes are larger than most other gulls, which allows more light to filter in and make the gull see easier at night. Melatonin levels in this species was measured and it was discovered that they have smaller amounts of melatonin than day-active gulls. A high level of melatonin usually makes birds sleepy. Little is understood if the melatonin levels are a cause or an effect of the Swallow-tailed Gull’s night time activity.

The Swallow-tailed Gull begins to breed at about 5 years old. Breeding pairs generally mate year after year. Most breed throughout the year in mixed colonies. The nest is usually on a small platform on a cliff about 30 – 35 feet above sea level. The nest is made of small pieces of lava, white coral, and sea urchin spines that help keep the eggs from rolling out of the nest. Nesting birds generally face the cliff, a habit exclusively common among cliff nesting gulls. The female lays one egg per clutch, and can breed throughout the year (mostly on nine-month cycles). The egg is incubated for 31 to 34 days and the young flies at about 60 to 70 days old. Both adults feed the chick for about 90 days. The adult hunts for food for the young near the colonies.

The population size of this species has been estimated at about 35,000 individuals in 2004. It currently has no endangered status.

Image Caption: An adult Swallow-tailed Gull with a chick on Genovesa Island, Galapagos Islands, Ecuador. Credit: Claumoho/Wikipedia (CC Attribution 2.0)

Swallow-tailed Gull Creagrus furcatus