Heermann's Gull heermannii

(last update: 23-01-2018 )

Coordinators:
John Cant
Mars Muusse

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adult: January

Below you will find a description of Chapter 16 HEERMANN'S GULL Larus heermanni, as published in one of the best Gull publication: "Gulls of the Americas" by Steve Howell & Jon Dunn.

"we" in the text below refers to the original authors. If any errors occur in this text, please let me know and mail to marsmuusseatgmaildotcom.

HEERMANN'S GULL Larus heermanni

LENGTH 18-20 IN. (45.5-50.5 cm)

IDENTIFICATION SUMMARY

This attractive, medium-sized, four-cycle gull breeds in nw. Mexico and is a regular post-breeding visitor north along the Pacific Coast to s. Canada, casually to se. Alaska. Bill average in depth with slight gonydeal expansion; tail tip falls between tips of P6 and P7 at rest. All ages are dark slaty gray to sooty brown overall with black legs. Alternate adult has a clean white head and mostly red bill; immature bills are pinkish to reddish basally. No other all-dark gull occurs regularly in its range.

TAXONOMY
Monotypic.

STATUS AND DISTRIBUTION
Endemic to W. N. America.

Breeding.

Breeds (Apr.-July) and partly resident in the Gulf of Calif., Mex., with 95 percent of the nesting population on Isla Rasa (which has 300,000-400,000 adults(1), and south locally to n. Jalisco and off Pacific Coast of cen. Baja Calif. Peninsula. Has nested on 19 islands in w. Mex., but during 1999 to 2000 bred on only 12 islands there(2). Since 1979, a few pairs have attempted nesting in coastal cen. Calif. (San Luis Obispo Co. north to San Francisco Co.(3); in 1990, hybridized with California Gull in Nevada.(4)

Nonbreeding.

Post-breeding dispersal (mainly June-Nov.) mostly north along Pacific Coast of N. America, regularly north to sw. B.C. (mainly s. Vancouver Is.); also south to cen. Mex., where uncommon to fairly common south to Colima, rare or casual south to Caxaca and Guatemala. Fairly common to common (mainly May-Feb.) along both coasts of Baja Calif. Peninsula (casual inland). Northbound movement in Calif. and Ore. Evident by June (a few birds in May), with numbers increasing dramatically after mid-June; peak numbers on cen. Calif. coast mid-July-Nov. Farther north, a few appear in sw. B.C. by June-early July, with peak numbers in coastal Wash. and sw. B.C. Aug.-mid-Oct., after which there is rapid southward withdrawal. Casual (Aug.-Sept.) north to se. Alaska. Often remains common in Ore. and n. Calif. until mid-Nov., in s. Calif. into Feb. Rare north of cen. Calif. after Dec., although some non-breeders remain in cen. and s. Calif. through spring. Uncommon more than about 50 km offshore. Casual inland in Wash., along coastal slope of Ore. (west of the Cascades), and Calif. (late Aug.—mid-Nov), exceptionally in small flocks.

Well away from the coast, most frequently found at Salton Sea (where rare; mainly mid-Apr.-early Oct., casually into winter), with scattering of records (Apr.-Oct.) elsewhere in se. Calif. (north to at least Mono Co.) and north to Nev. Casual (mainly Sept.—Nov.) along Colo. R. north to Lake Mead (Ariz./Nev.), and elsewhere in Ariz.

Accidental (mainly Aug.-Dec.) east in N. America to Great Lakes, Va., Fla., and s. Tex., with some individuals remaining many months, for example, Aug. 1979 to Nov. 1981 in Mich./Ohio, Nov. 1999 to Sept. 2000 in Ont., and Oct. 2000-Aug. 2004 or later in Fla.

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