Common Gull

识别特征

Adult common gulls are 40–46 cm (16–18 in) long, noticeably smaller than the herring gull and slightly smaller than the ring-billed gull. It is further distinguished from the ring-billed gull by its shorter, more tapered bill, which is a more greenish shade of yellow and is unmarked during the breeding season. The body is grey above and white below. The legs are yellow in breeding season, becoming duller in the winter. In winter, the head is streaked grey and the bill often has a poorly defined blackish band near the tip, which is sometimes sufficiently obvious to cause confusion with ring-billed gull. They have black wingtips with large white "mirrors" on the outer primaries p9 and p10, which are smaller than those in the short-billed gull. Young birds have scaly black-brown upperparts and a neat wing pattern, and pink legs which become greyish in the second year before tuning yellow. By the first winter, the head and belly are white, with fine streaks and greyish feathers grow on the saddle. They take three years (up to four in the Kamchatka subspecies) to reach maturity. The call is a high-pitched "laughing" cry.

分类信息

There are three subspecies, with the Kamchatka gull (L. (c.) kamtschatschensis) being considered a distinct species by some authorities. <p>The North American short-billed gull was formerly widely considered conspecific with this species (as Larus canus brachyrhynchus), but most authorities now recognize it as a distinct species, L. brachyrhynchus, based on differences in genetics, morphology and vocalizations. Though "mew gull" was formerly used as a name for Larus canus sensu lato in North America and not commonly used outside North America, the name "short-billed gull" was chosen for L. brachyrhynchus by the AOS due to the usage of mew gull in recent literature to denote all forms of the L. canus complex, the revival of the name short-billed gull in some of the same literature for brachyrhynchus, and the fact that short-billed gull was historically used for brachyrhynchus when it was treated as a distinct species in the first through third editions of the AOU (now AOS) checklist (in which the name mew gull, contrary to more recent usage, was specifically reserved for the Old World forms).

学名

Larus canus

命名信息

Linnaeus, 1758

目

Charadriiformes

科

Laridae

属

Larus

分布与栖息地

繁殖区

NA, PAL : Iceland and nw, c Europe to Kamchatka (e Siberia)

非繁殖区

Europe to n Africa, Mediterranean, Black and Caspian seas, Persian Gulf; Sea of Okhotsk (se Russia), Japan, Korean Pen. to se China

迁徙

Complete migrants

行为

Both common and short-billed gulls breed colonially near water or in marshes, making a lined nest on the ground or in a small tree; colony size varies from 2 to 320 or even more pairs. Usually three eggs are laid (sometimes just one or two); they hatch after 24–26 days, with the chicks fledging after a further 30–35 days. Like most gulls, they are omnivores and will scavenge as well as hunt small prey. The global population is estimated to be about one million pairs; they are most numerous in Europe, with over half (possibly as much as 80-90%) of the world population. By contrast, the short-billed gull population in Alaska is only about 10,000 pairs.

保护状况

种群趋势

unknown