Swallow-tailed Gull

The Swallow-tailed Gull, Creagrus furcatus, is a distinctive member of the gull family Laridae, and the sole species within its genus. This equatorial seabird is recognized by its elegant forked tail and the remarkable transformation of its plumage and eye coloration between breeding and non-breeding seasons. During breeding, adults boast a striking black head and a vivid red eye-ring, which transitions to a white head and black eye-ring when not breeding. Their upperparts are a sleek gray, with black wingtips accentuating their silhouette, and the bill is predominantly black with a stark white tip.

Identification Tips

To identify the Swallow-tailed Gull, look for the unique combination of its forked tail, the seasonal variation in head color, and the red or black eye-ring depending on the breeding cycle. The large, dark eyes are also a key feature, adapted for their nocturnal lifestyle.

Habitat

The Swallow-tailed Gull is intimately tied to the marine environment, spending the majority of its life soaring over the open ocean. It breeds on the rocky cliffs and shores of the Galápagos Islands, favoring the eastern islands where the waters are warmer.

Distribution

This gull is a near-endemic breeder to the Galápagos Islands, with a few pairs nesting on Colombia's Malpelo Island. Outside the breeding season, it adopts a pelagic lifestyle, migrating eastward to the coasts of Ecuador and Peru.

Behaviour

The Swallow-tailed Gull is the world's only fully nocturnal gull and seabird, feeding on squid and small fish that surface at night. At dusk, flocks depart the colony amidst a cacophony of calls and displays, returning before dawn.

Song & Calls

The vocal repertoire of the Swallow-tailed Gull is quite distinct from other gulls, with a "rattle-and-whistle" alarm call and a rapid "kweek, kweek, kweek" greeting call between mates. These sounds are integral to their social interactions, particularly during the breeding season.

Breeding

Breeding commences around the age of five, with pairs often remaining together across seasons. The Swallow-tailed Gull nests on cliffs, constructing a platform adorned with lava pieces, coral, and sea urchin spines to secure the egg. Typically, one speckled egg is laid per breeding attempt, with a nine-month breeding cycle that may shorten if the egg or chick is lost. Incubation lasts about 31-34 days, and fledging occurs at 60-70 days, with parental care extending until around 90 days of age.

Similar Species

While the Swallow-tailed Gull's nocturnal habits and breeding plumage make it quite unique, it shares some nesting behaviors with the cliff-nesting Black-legged Kittiwake.

Diet and Feeding

The diet of the Swallow-tailed Gull consists exclusively of nocturnal prey, such as squid and small fish that ascend to feed on plankton at night. This gull's large eyes and reflective tapetum lucidum aid in its nighttime foraging.

Conservation status

As of the last assessment in 2004, the Swallow-tailed Gull is classified as Least Concern by the IUCN, with an estimated population of around 35,000 individuals. There are currently no significant threats identified that could endanger its population.