Larus crassirostris Vieillot, 1818

Taxonomy and Size

The black-tailed gull, scientifically named Larus crassirostris Vieillot, 1818, is a medium-sized gull. It measures 46 cm (19 inches) in length, with a wingspan of 126–128 cm (49.6–50.3 inches).

Adult Appearance

It has yellow legs, a red and black spot at the end of its bill, and, as its common name suggests, a black tail. Males and females have identical plumage and features, though males are larger than females.

Plumage Development

It takes four years for black-tailed gulls to develop full adult plumage.

Etymology of Common Names

This gull produces a cat-like call, which inspired its Japanese name umineko (meaning "sea cat") and its Korean name gwaeng-yi gull (meaning "cat" gull).

Cultural Significance

In Hachinohe, the calls of this species are counted among the 100 Soundscapes of Japan.

Resident Distribution

This species is resident along the coastlines of the East China Sea, Japan, Manchuria, and the Kuril Islands.

Vagrant Records

It occurs as a vagrant in Alaska and North America, and individuals have also been recorded in the Philippines.

General Diet

Black-tailed gulls feed mainly on small fish, molluscs, crustaceans, scraps, and carrion.

Diet Composition Study

A study of identifiable remains in gull excreta from Korea found 19.1% of remains were fish, 3.3% were crustaceans, and 3.3% were land insects.

Feeding Behavior

The species often follows ships and commercial fishing fleets, and it will also steal food from other seabirds.

Nesting Timing

It nests in colonies, which form in mid-April.

Reproduction Details

Females lay 2–3 eggs by early June, and incubation lasts approximately 24 days.

Vocal Signal Repertoire

Black-tailed gulls use a wide range of vocal signals, with over 10 distinct sounds used for communication.

Chick Recognition Ability

Chicks can recognize their parents through voice and visual cues between 10 and 15 days after hatching, and can also tell the difference between siblings and unrelated gulls.

Call Function Categories

Different call types serve different purposes: alarm calls are warning signals for predators or other danger; aggressive calls accompany attacks on predators; contact calls are for communication between members of the species.

Mew Call Usage

The most commonly heard cat-like "mew call" is a type of contact call, used frequently in situations including returning to the nest with food, switching mating and nesting roles, caring for young, and collective flight.

Additional Contact Call Types

Contact calls also include the begging call of young gulls and the call a female makes during mating.