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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