Bryan Brillhart Photography Presents “Dig Imperial Beach” Bird of the Week, the "Thayer's Gull"
Oct 13, 2016 08:13AM
● By Paul Spear
The column will provide a picture of a bird(s) locally photographed and we will have background on the bird.
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The Thayer's Gull
This week’s “Bird of the Week” is Thayer's gull (Larus thayeri), a large gull native to North America. Wintering commonly along parts of the Pacific Coast, this bird was largely overlooked for years because of its resemblance to Herring Gull (it was once considered a race of that species). Thayer's is a gull of the Canadian high Arctic in summer. It is closely related to the Iceland Gull, and the two are sometimes very difficult to tell apart; they may be only forms of the same species. Most birds are from the central Canadian Arctic and move southwest to the Pacific Coast. They are rare farther east in winter. Young birds tend to move farther south than adults; most are found in southern California and northwestern Mexico are first-winter immatures.
Adult Thayer's gulls in nonbreeding plumage have a pale gray mantle, with obvious blackish
wingtips, and extensive brown streaking on the head and neck. The head, neck, breast, belly, and underwings are primarily white, and the legs are pink. There is a red spot on the lower mandible, and the color of the iris is generally dark. In summer, the head and neck are white, with the bill turning bright yellow with a larger red spot on the lower mandible. Juvenile gulls are brown, with black bills, and black legs which quickly fade to adult pink. Thayer's Gull reaches a length of 56 to 64 cm (22 to 25 in), with a wingspan of 130 to 148 cm (51 to 58 in) and a weight of approximately 720 to 1,500 g (1.59 to 3.31 lb).
Habitat is along coastal waters, and bays. They winter mostly in coastal regions, especially around estuaries and protected bays, but also well offshore at times. They may regularly visit freshwater ponds and garbage dumps in coastal plains. Thayer’s gulls are rare in winter farther inland and around lakes, and rivers. Nesting is on the rocky coasts of northern islands.
Thayer’s gulls forage in flight by dipping to the surface of water or by plunging to just below the surface; also feeding while swimming or walking. They are omnivorous. Diet includes many small fish, also carrion, mollusks, crustaceans, and berries. Around colonies of smaller seabirds, they may take their eggs or young. They also may feed on refuse around garbage dumps, docks, and fishing boats.
Breeding behavior is not well known. Thayer’s gulls probably do not breed until 4 years old. Nests are in colonies, sometimes with other species of gulls. Nest sites are on ledges of rocky cliffs close to the ocean, usually facing a fjord or sound on arctic islands. Nests (probably built by both sexes) are a low mound of plant material with a depression at the center.
After breeding, females lay 2, sometimes 3, buff to olive or gray with darker brown blotches
eggs. Incubation is probably by both sexes; and their incubation period is not known. Both parents probably feed their young. Age of young at fledging and at independence are not known.
Thayer’s gulls will soon be migrating into our terrific Tijuana Estuary along our beaches. Look for them while on a beach walk to the Tijuana River. Until next week, happy birding!