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Slaty-backed Gull


First Cycle
Second Cycle
Third Cycle


SLATY-BACKED GULL (24"-27"; 52"-54") schistisagus

BILL SHAPE: fairly thick and straight, may appear stubby; 4-5x eye diameter; gonydeal angle small. to moderate.
HEAD SHAPE: rounded to low sloped forehead, flat crown w/ squared-off rear crown
WING EXTENSION: about bill length
POSTURE/HABITS: often very bulky or wide-bodied (like a goose from behind); may appear long-necked when standing
BILL COLOR: black w/ pinkish base to lower mandible and a touch at base of culmen; pale tip by summer pale yellow to black w/ pink base to lower mand; variable dark subterm band ... ...
LEG COLOR: bright pink or dark pink bright to dark pink bright to dark pink bright pink, even reddish
IRIS/ORB RING: dark often pale yellow pale yellow pale yellow or cream to light amber; orb ring red to pink
HEAD: quite pale with dark gray smudge in front and immediately around eye; creamy brown blurred streaks on rear crown and nape mostly white w/ light streaking on crown and aur edge; dark streaks on nape and neck side; dark smudge around eye same as adult obvious dark gray smudge around eye, extending more in front and behind; otherwise variable thin brownish streaks over aurs, rear head, and neck; many white-headed by late Jan
UNDERPARTS: light blotching on breast, becoming nearly solid and darker on belly; undt. coverts barred breast pale and blotchy; belly blotchy or solid dark; undt covs may have pale bars mod blotching on lower breast and belly white
med. dark brown, not black, w/pale crecents like Thayers but sometimes larger, w/ pale edge extending along upper (inner) edge of the feathers med dark brown, not black, w/ pale cresents or tiny A-spots as adult w/ A-spots, but spots may be smaller black w/ A-spots; A7 larger than eye; A8-10 same or smaller than eye
(in flight):
dark brown on outermost Ps with slightly pale window on inner Ps (becoming more obvious in late winter), w/ dark subterminal spots in window; very pale or silvery from below, with thin dark trailing edge and dark P9-10 outer Ps dark brown, inner Ps virtually white above; pale silvery below, w/ outer Ps slightly darker usually shows small mirrors and white tongues of adult large mirror on P10; often small mirror on P9; large white tongues on P6-7 and usually P8, called a "string of pearls", obvious from above and below; black parts are dark gray below
(in flight):
solid dark brown above; silvery from below med brown w/ large pale fringe and edges, creating weak dark bar above; pale silvery from below ... adult gray w/ broad white trailing edge, about 3/4 bill length; may show thin white skirt when perched
TERTIALS: moderate dark brown (slightly lighter than Ps), w/ broad pale tip or subterm chevron; may show pale edges med brown w/ irregular but heavily mottled tips adult gray w/ white tertial crescent about 1/2 - 3/4 bill length adult gray w/ large white crescent, about 3/4 bill length
GREATER COVERTS: variable; fairly solid med g-b (slightly lighter than Ts) on darker birds; fading to white quickly, often showing 2 rows of faded dark spots solid rather pale g-b w/ fine internal marbling near tips; fading to white by summer muddied adult gray and brown adult gray
LESSER & MED COVERTS: creamy white w/ dark subterminal anchors, giving a pale look to upperwing; prone to fade largely pale cream w/ irreg small dark subterm anchors or shafts; prone to fade muddied adult gray and brown adult gray
SCAPULARS: pale gray with thin black shaft lines and variable pale tip; not checkered like M&L covs or w/ some adult gray; may show white crescent as adult but with smaller white crescent adult gray w/ white crescent about 1/2 bill length
BACK: same as scapulars adult gray or like muddied 1W as adult adult gray is very dark gray, darker than Vega
RUMP: variable, mottled w/ dark; pale by summer white white white
TAIL: almost solid dark brown; pale fringe; fine white bars on outermost webs; irreg pale bars at base of outer retrices solid dark brown w/ pale fringe and slighly mottled pale bases to outer retrices w/ pale bars at base of outermost webs mostly blackish w/ white fringe and extensive white mottling to bases, producing jagged look white

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