The black-tailed gull is a distinctive seabird, native to the coastlines of East Asia, where it is a common sight. Its adaptable nature allows it to thrive in various marine environments.
Identifying the Black-tailed Gull
Adult black-tailed gulls are easily recognized by their black tail band, which gives the species its name. They possess yellow legs and a yellow bill marked with a black band and a red spot at the tip. The adult plumage, which takes about four years to fully develop, includes a dark gray back and wings with black wingtips that lack white mirrors.
These gulls are comparable in size to a crow or a herring gull, measuring approximately 46 cm (18 inches) in length with a wingspan of 126–128 cm (49.6-50.3 inches). In winter, their heads show strong brown streaking, while first-winter birds are dark brown with a paler face. Immature birds are more challenging to identify, but they gradually develop adult features.
Habitat and Distribution
The black-tailed gull is found along the coastlines of East Asia, including the East China Sea, Japan, Manchuria, and the Kuril Islands. It is a resident species in these areas, though some post-breeding dispersal occurs. The gull prefers habitats such as sea cliffs, rocky or sandy seashores, and rocky islets for breeding.
Outside the breeding season, black-tailed gulls disperse, often remaining within Southeast Asian waters, though some venture offshore. While common in its native range, the species has been observed as a vagrant in other areas, including Alaska, North America, and the Philippines. In Japan, large colonies are found, with over 40,000 gulls nesting at Kabushima, designated a National Natural Monument.
Diet and Foraging Behavior
The black-tailed gull is an opportunistic feeder, primarily consuming small fish, mollusks, crustaceans, and carrion. These gulls also readily exploit discarded human food and refuse.
Their foraging techniques are varied, including surface-seizing prey from the water, sometimes immersing their heads, or plucking items while wading or walking on the ground. They also drop hard-shelled prey onto firm surfaces to break them open. The species is known to follow ships and commercial fishing fleets, and it engages in kleptoparasitism, which is the act of stealing food from other seabirds.
Breeding and Social Habits
Black-tailed gulls are colonial breeders, forming dense aggregations that number up to 10,000 pairs. The breeding season occurs in spring and early summer. Nesting sites are on sea cliffs, rocky coastlines, or sandy shores.
Females lay two to three whitish eggs with dark markings, and incubation lasts about 24-25 days. Both parents participate in feeding and rearing the downy chicks, which fledge about 35-40 days after hatching. The gulls are monogamous and highly vocal within their colonies, known for their harsh, cat-like calls.