The endemic Swallow-tailed Gull (Larus furcatus, gaviota de cola bifurcada) is the only nocturnal gull in the world. Adults have a distinctive black head with a red ring around the eye, black bill with a gray tip, white, forked tail, and red, webbed feet. They often have white spots on their back, which resemble guano and help them to camouflage with their rocky cliff habitat. Immature gulls are white with dark brown spots on their backs and a black band on their tails.
Swallow-tailed gulls nest in small colonies on islands concentrated in the eastern archipelago, breeding all times of year. Their courtship ritual involves mutual preening, head-tossing, and regurgitation of food by the male. The young have a recognizably harsh call, consisting of an initial scream that displays their red gape and tongue, an uncharacteristic rattle, and a final clicking noise, which may also be used for echo-location during night feeding.
The most common places to encounter swallow-tailed gulls are Genovesa and South Plaza.