[order] Charadriiformes | [family] Laridae | [latin] Larus delawarensis | [UK] Ring-billed Gull | [FR] Goéland à bec cerclé | [DE] Ringschnabelmöwe | [ES] Gaviota de Delaware | [IT] Gabbiano di Delaware | [NL] Ringsnavelmeeuw

Ringsnavelmeeuw determination

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Ring-billed gulls are medium-sized gulls. Males are larger than females. They are 46 to 54 cm long (average 50.2 cm) and weigh 400 to 700 g (average 550 g). Females are 43 to 50 cm long (average 46.9 cm) and weigh 300 to 600 g (average 470 g). Adults of both sexes have a wingspan of approximately 127 cm. The back and shoulders of ring-billed gulls are pale bluish-gray, and the head is white. The wings are tipped in black with evident white spots, and the belly is whitish. Ring-billed gulls have yellowish or greenish legs and feet. Their most distinctive feature is a sharply defined narrow black band that encircles the bill. Immature ring-billed gulls have different coloration than adults. First year birds are whitish with brown flecks and have very dark wing tips and tails. Second year birds are more like the adults, but have a black-tipped tail.

These birds frequent inland waterways. They may be found in areas with sandy ground where vegetation is sparse. They may also be found where there are rocks and concrete pieces, on pebble beaches, and sometimes in wet meadows. Their preference for open areas makes them well-suited to urban and suburban landscapes and they are often found on large, grassy lawns, parking lots, and in vacant land.

Ring-billed gulls range from southern Alaska to the north shore of the Gulf of St. Lawrence, to southern parts of Oregon and Colorado and northern New York. During the winter, it is found from British Columbia to Maine (including the Great Lakes and Maritime regions), then south to central California to southern Mexico to the Gulf Coast to Cuba. It is also found in Bermuda and Hawaii. This gull winters from southwestern British Columbia and Washington state to the Great Lakes region to Nova Scotia then southward.

Ring-billed gulls are opportunistic feeders, or scavengers, meaning they will eat almost anything that they find. They eat fish, rodents, small aquatic animals, bird chicks and eggs, insects, and vegetable matter such as fruits, though they prefer animal foods.
This kind of feeding behavior has made them very successful in areas around humans where they take advantage of land fills, garbage dumps, and ships that dump garbage overboard. They also scavenge from plowed fields, parks, and parking lots. In fact, these gulls might be seen squabbling over discarded items from fast-food restaurants. Ring-billed gulls are able to snatch food from the water's surface while in flight.

This species has a large range, with an estimated global Extent of Occurrence of 5,400,000 km². It has a large global population estimated to be 2,600,000 individuals (Wetlands International 2002). Global population trends have not been quantified, but the species is not believed to approach the thresholds for the population decline criterion of the IUCN Red List (i.e. declining more than 30% in ten years or three generations). For these reasons, the species is evaluated as Least Concern. [conservation status from birdlife.org]

Ring-billed gulls are generally monogamous. Breeding pairs form immediately before or during arrival on the breeding grounds and territory establishment. In expanding colonies, polygynous trios (two females attending the same nest and mated to the same male) are frequently observed.
Ring-billed gulls nest in colonies on the ground, or infrequently, in trees near inland lakes. Nests are built by both members of a breeding pair. Nests are constructed of dead plant material including twigs, sticks, grasses, leaves, lichens and mosses, and may be interspersed with those of other water birds.
The female lays 2 to 4 (usually 3) eggs per clutch, each about 6.4 cm long by 4.6 cm wide. The eggs are light blue, green or brownish and spotted. Both male and female incubate the eggs. The semiprecocial chicks hatch after 20 to 31 days, and are brooded and fed by both parents. The chicks begin leaving the nest within days of hatching, and are able to fly at about 5 weeks old.

Wanders N to Alaska and Yukon. Winters from S part of breeding range S to Greater Antilles; becoming commoner in Central America, both in the interior and along coasts; also occurs increasingly in Lesser Antilles; first recorded in Florida in 1930, now common in winter. E population migrates to Atlantic coast and S to Gulf Coast, few reaching West Indies and Central America. Birds of plains and mountain states move to pacific coast. Large numbers remain on Great Lakes until freeze-up. Most Great Lakes birds return to the lake where they hatched, but not necessarily to same colony. Since mid-1970's has become regular vagrant to W Palearctic (see page 595), especially in British Is, where records span all months of the year; massive influx of over 400 individuals in first half of 1980's has led to species becoming a virtual resident in some coastal areas.