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Black-tailed Gull (crassirostris)


IMAGES:

Adult


DESCRIPTION:

BLACK-TAILED GULL(18"-19"; 48"-51") crassirostris

BILL SHAPE: long w/ slightly downcurved tip; slight gonydeal angle; 4.5 times eye diameter
HEAD SHAPE: sloped forehead w/ evenly rounded crown
WING EXTENSION: quite long; about 1.5 times bill length
POSTURE/HABITS: about size of California Gull
FIRST CYCLE SECOND CYCLE ADULT
BILL COLOR: flesh or pink w/ square-cut black tip pale yellow-green w/ black subterm band and faint reddish tip pale yellow w/ small red gon. half-spot; black subterm band; red tip
LEG COLOR: pale pinkish-brown pale green to pale yellow yellow
IRIS/ORB RING: dark pale gray to brown; orb ring dark cream to pale yellow; orb ring dark red to black
HEAD: white forehead, lores, throat, and broken eye-ring; fades into smooth unstreaked fawn brown crown, auriculars, and darker nape white w/ gray streaks across rear half, darkest across lower nape; broken white eye ring may show through gray tinge white w/ light streaks fading into a darker band from aur. edge to rear crown, giving a partial hooded or collared look; broken white eye ring may show
UNDERPARTS: smooth brown upper breast, fading to white belly and undt coverts white w/ variable g-b wash or mottling on breast sides and flanks white
PRIMARIES
(folded):
brownish-black as adult but A-spots smaller or absent black w/ A-spots; A10 smaller than eye; others same or larger
PRIMARIES
(in flight):
solid brownish-black above and below as adult, but color black-brown; A-spots smaller; more black on P4-5 P7-10 black w/ small A-spots; no mirrors; P6 black outer web and base w/ A-spot; P4-5 black band w/ A-spot;similar from below, but gray paler
SECONDARIES
(in flight):
solid brownish-black w/ pale tips above and below as adult but w/ thinner trailing edge gray w/ white trailing edge, 1/3-1/2 bill length; paler from below
TERTIALS: dark brown w/ gray fringe as adult but crescents may be more washed out gray w/ faded white crescents about 1/3 bill length
GREATER COVERTS: solid med. brown w/ faded pale brown edges adult gray, tinged brown adult gray
LESSER & MED COVERTS: as tertials, but paler adult gray , tinged brown adult gray
SCAPULARS: pale gray, fading to darker brown subterminally, w/ pale fringe as adult but slight brown tinge adult gray w/ small white crescent, about 1/3 bill length
BACK: as scapulars as scapulars adult gray is medium dark, darker than Calif. Gull
RUMP: quite white w/ dark chevrons and irregular spots white white
TAIL: solid brownish-black w/ buff fringe as adult but black band broader, making tail mostly black white w/ crisp broad black sub- term band w/ jagged base; outer webs white

The was table created by Steve Hampton and is intended to futher our knowledge of gull identification. Please email me at shampton@ospr.dfg.ca.gov if you have any suggestions for updating or improving this table. Thanks.