Black-Tailed Gulls
Kabushima is an important breeding ground for umineko, the black-tailed gulls (Larus crassirostris) that are symbols of the island. Kabushima is a safe and plentiful feeding ground, and the gulls have flocked here for centuries.
Black-tailed gulls typically reach a length of 44 to 48 centimeters and weigh up to 0.6 kilograms. They are recognizable by their white and grey plumage, the red spot on their bills, and their black tail feathers. As many as 40,000 gulls flock to the island to nest, and their mating cycle lasts about six months.
Around February, the gulls migrate as couples to Kabushima from coastal areas throughout Japan. The black-tailed gull is monogamous, and pairs that have previously mated commonly return together. In early March, the gulls prepare for their stay on the island. During this period, it is common to hear the distinctive cat-like cry of the birds, which inspired their name—umi means “sea,” and neko means “cat.” Males can also be seen engaging in aggressive displays of territorial behavior.
Mating, nest building, and incubation take place from the end of March through mid-May. The gulls build nests by digging small holes with their feet, which they line with grasses and other materials. They can lay from one to five eggs, which are about the same size as a chicken egg, and are olive-colored with black speckles. Once the eggs are laid, both the male and female will take turns incubating them for hours at a time. The eggs hatch about 26 days later and, in a typical year, most eggs will have successfully hatched by mid-June.
The chicks of black-tailed gulls have black, wispy feathers. Due to the cool winds off the Pacific Ocean, they spend most of their time nestled against their parents for warmth. The parents protect and feed their offspring for about 45 days.
By mid-to-late July, the chicks will have reached their full size, and begin to practice flying. By August the young have mastered this skill, and flock by flock the gulls will depart Kabushima, to return the following year.