Appearance

Studies of molts and plumages (Dwight 1901, 1920, 1925) give few data; instead give brief and general descriptions of extent of each molt and appearance of each resulting plumage. Dwight did not describe sequence of replacement of feathers in each molt or relative timing of molts (1) between sexes, (2) among age classes, (3) among different populations, or (4) in relation to ecological factors such as effect of failed (or unattempted) versus successful breeding. Such studies in North America are needed.

The scenario presented below depicts the sequence of molts and plumages for an average individual. Great Black-backed Gulls typically do not achieve Definitive plumage until >3 yr old (i.e., during their fourth Prebasic molt), but there is considerable individual variation in the age at which this plumage is attained (Dwight 1925, Witherby et al. 1941).

Hatchlings

Semiprecocial and downy. Down paler or purer gray than that of Herring Gull, grading to buffish white on belly; underparts are palest on chin and throat and unmarked except for spots on side of chin and an obscure speckling or clouding on sides, posterior abdomen, and undertail-coverts. Head whiter than that of Herring Gull, finely marked with sparse, small, dotlike fuscous black to deep gray spots that are star-shaped to polygonal in shape; back, thigh, and undertail-coverts are diffusely mottled with drab gray to light clove brown. Back less heavily marked than that of Herring Gull; as in Herring Gull, dusky spot on shoulder and 2 blurred bars across forearm. Small median spot or line on forehead; very variable spot on anterior crown, which diverges into 2 less-defined rows of spots in temporal region. Median spot, transverse group of spots, or 2 spots—one behind the other—on occiput; often an additional large spot to each side of occiput. Spots also on lores, relatively smaller spots around orbital area, and none within orbital area; irregular spots on cheek, throat, and side of neck, forming 2 pairs of larger spots on nape (Dwight 1925, Witherby et al. 1941, Fjeldså 1977, Cramp and Simmons 1983).

Juvenal Plumage

Prejuvenal molt complete; sheds down progressively over 30–40 d; down molts first from scapulars, wings, breast, and back, then from underside, neck, and head. Down retained on head after remainder of body is fully feathered; Juvenal plumage typically complete by 4–6 wk after hatching (Witherby et al. 1941).

Head and underparts sparsely and distinctly streaked gray brown; paler face and nape; darker ear-coverts; blackish eye-crescent. Mantle and scapulars boldly patterned blackish brown; whitish edges form contrasting checkered pattern. Rump white and sparsely marked by thin subterminal arrowheads and shaft-streaks. Pattern of wing-coverts more barred and less checkered than mantle and scapulars; transverse pale bar separated from edge of feather by thin dark outline, forming 2 oval patches. Tertials blackish brown, with obvious pale border and obvious pale notches at sides, and subterminal pale bar. Secondaries mainly blackish brown, forming secondary bar. Primaries and outer wing mainly blackish brown, but inner primaries pale with dark subterminal marks forming pale window. Underwing has slight window effect; rest of underwing is uniform blackish brown, giving subtle 2-tone effect. Tail white with dark zigzag bars and spots at base; blackish subterminal band typically highly diffuse and broken; broad white tip (color plates in Cramp and Simmons 1983, photos and line drawings in Grant 1986).

Basic I Plumage

Prebasic I molt partial; includes head, neck, many or most mantle-feathers, some scapulars, some rump-feathers, and breast and sides. All Juvenal flight-feathers retained. Molt begins Aug–Nov (rarely later), typically ending by Dec. Prebasic I and Prealternate I molts overlap in some individuals (Dwight 1925, Cramp and Simmons 1983). Head, neck, and underparts whiter than in Juvenal plumage; back grayer brown than in Juvenal plumage.

Alternate I Plumage

Prealternate I molt partial; occurs Mar and Apr, though some may start earlier; chiefly confined to head, in some to most of back, rump, and underparts (Dwight 1925, Cramp and Simmons 1983).

Alternate I plumage similar to Juvenal and Basic I plumages, except head and underparts often extensively whitish. Mantle more uniformly dark, with less-contrasting checkered pattern (color plates in Cramp and Simmons 1983, photos and line drawings in Grant 1986).

Basic II Plumage

Prebasic II molt complete. Occurs Jul–Sep, in European populations as early as end of May (Dwight 1925) or Apr (Witherby et al. 1941), and lasting until Oct (Grant 1986). Flight-feather molt begins with innermost primary (P1, not P10 as stated by Grant [1986], who followed Dwight’s long-abandoned numbering system) and its associated greater-covert, and progresses outward to outermost primary (P10). At any one time, only 2 primaries typically are growing. Secondary molt starts simultaneously from both outermost secondary (S1) inward, and from innermost secondary (S24) outward, beginning at about the time P6 and P7 are growing. Secondary molt proceeds much more rapidly than primary molt, many feathers often missing at one time, typically finishing before completion of primary molt. Rectrix molt begins shortly after onset of secondary molt, usually beginning with central pair and proceeding outward. Some birds replace R6 before R5, and some individuals may lose all rectrices synchronously. Wing-coverts other than greater primary-coverts molt just before secondary molt, beginning with median-coverts and progressing to greater- and lesser-coverts. Molt of underwing-coverts is prolonged; spans entire molt period. Body molt usually begins on back, followed shortly thereafter by humeral and ventral tracts, and anterior part of head. Thereafter, body molt progresses outward in all directions. All subsequent Prebasic molts follow same sequence (line drawings of primary and rectrix color pattern in Dwight 1920, color plates in Cramp and Simmons 1983, photos and line drawings in Grant 1986).

Head and back of neck white, usually with narrow indistinct streaking; underparts and rump mainly white, with less coarse dark streaking on breasts, sides, and flanks; mantle and scapulars grayer; some mantle-feathers and scapulars are uniform gray black with brown tinge and often brown tip. Outer wing mainly blackish brown (P10 often with irregular gray white mirror at tip), but P1–P5 and their greater primary-coverts are mainly pale gray brown; tertials barred black and white or with extensive white internal markings, not mainly dark-centered as in previous plumages and with variable amount of brown barring; greater-coverts are peppered or finely barred, but not strongly barred as in previous plumages. Underwing generally whiter. Uppertail-coverts are more closely barred than in Basic I plumage. Tail extensively whitish at base; remainder mainly solid blackish, broken up by white or whitish wavy bars.

Alternate II Plumage

Extent and timing of Prealternate II molt same as for Prealternate I molt. Plumage same as Basic II plumage, except head and underparts less streaked. Mantle and scapulars have more black, sometimes with a few brown-barred feathers. Dark areas on wings and tail faded, and pale areas faded to whitish (often contrasting with dark mantle and scapulars to give saddle effect) by summer.

Basic III Plumage

Extent and timing of Prebasic III molt same as for Prebasic II molt (Dwight 1925, Cramp and Simmons 1983). Head and body white, with faint streaking primarily on nape and hindneck; a few streaks on undertail-coverts. Mantle and scapulars uniform blackish gray, with occasional scapular as in Basic II plumage. Wings as in Definitive Basic plumage; uniform black except extent of black on distal portion of primaries decreases toward more proximal primaries and is more extensive than in Definitive Basic plumage—i.e., black tips extend to primaries more proximal than P5 (typically innermost primary with black tip in Definitive Basic plumage). Greater primary-coverts and alula also black-tipped. Outer primaries with black also have white mirrors, though smaller, less numerous, and on fewer primaries than in Definitive Basic plumage. Variable amount of brown markings on inner wing, especially on median- and lesser-coverts, secondaries and their greater-coverts, and tertials (which are mainly blackish brown); brown markings less extensive than in Basic II plumage. Underwing white (sometimes with some brown marks on coverts) with dark subterminal trailing edges. Rump and uppertail-coverts white, with a few brown marks. Tail white, with subterminal markings of highly variable extent and pattern; markings typically finely barred or freckled or often confined to feather centers, giving tail dark-and-white striped pattern (line drawings of primary and rectrix color pattern in Dwight 1920, color plates in Cramp and Simmons 1983, photos and line drawings in Grant 1986).

Alternate III Plumage

Extent and timing of molt same as for Prealternate I molt. Plumage same as Basic III plumage, except head, neck, rump, and underparts pure white or with a few dark streaks; freckled areas on inner wings are worn or faded to whitish; white primary tips are reduced or lacking because of wear (Grant 1986).

Definitive Basic Plumage

Extent and timing of Definite Prebasic molt same as for Prebasic III molt. Molt typically begins during egg-laying, incubation, or shortly after hatching. Head and neck white, or lightly streaked with dusky brown; rump, underparts, and tail white. Mantle slaty to sooty black; secondaries and tertials gray black like mantle and broadly edged with white. Black primary markings usually terminate with subterminal spot on P5, forming clear-cut black wing-tip above and below; some individuals also have small blackish marks on outer greater primary-coverts. White mirrors larger, more numerous, and on more primaries. Mirrors on P9 and white tip on P10 are obvious at long distance. No brown markings on inner wing or underwing; underwing white with broad, dark gray subterminal trailing edge, which merges with blackish underside of outer primaries. Scapular-crescent small; tertial-crescent prominent when bird is perched. Thin white leading edge prominent; white tips of secondaries and inner primaries form prominent trailing edge (line drawings of primary and rectrix color pattern in Dwight 1920, color plates in Cramp and Simmons 1983, photos and line drawings in Grant 1986).

Definitive Alternate Plumage

Extent and timing of molt same as for Prealternate I molt. Plumage same as Definitive Basic plumage, except head, neck, upper mantle and tail-coverts, and underparts white; white tips of primaries reduced through wear (line drawings of primary and rectrix color pattern in Dwight 1920, color plates in Cramp and Simmons 1983, photos and line drawings in Grant 1986).

Aberrant Plumages

No total albinistic or melanistic birds have been reported in North America; one North American sight record of a bird (presumably adult) with 5 white primaries in each wing (Ross 1963).

The following based on Dwight 1925, Witherby et al. 1941, Fjeldså 1977, and Cramp and Simmons 1983 .

Bill And Gape

Hatchlings. Bill black at base, with pinkish buff tip.

Juvenal Plumage. Bill brown black, white at tip; flesh pink area at base of lower mandible.

Basic I Plumage. Bill black, dusky gray pink at base.

Alternate I Plumage: White area at tip of bill and pale area at base more prominent.

Basic II Plumage. Bill pale pink at base, with large subterminal black band extending proximally along cutting edge.

Alternate II Plumage. Bill usually pale yellow or pink, with subterminal black band and black cutting edge.

Basic III Plumage. Bill more extensively yellow, creamy, or yellow pink, with variable amount of orange or pale red at gonys.

Alternate III Plumage. Unchanged from Basic III plumage.

Definitive Basic Plumage. Bill paler and duller than in Definitive Alternate plumage; gape pinkish.

Definitive Alternate Plumage. Bill pale yellow with pale bone-colored tip; bright vermilion patch at gonys and sometimes small dusky spot near tip of lower mandible; gape vermilion.

Iris

Hatchlings. Dark brown.

Juvenal Plumage. Dark olive brown or black brown; eye-ring yellowish brown.

Basic I Plumage. Unchanged from Juvenal plumage.

Alternate I Plumage. Unchanged from Juvenal plumage.

Basic II Plumage. Sometimes pale; eye-ring yellowish to dull orange.

Alternate II Plumage. Often pale.

Basic III Plumage. Probably always pale.

Alternate III Plumage. Unchanged from Basic III plumage.

Definitive Basic Plumage. Pearl gray with granulated appearance or blue gray, sometimes pale yellow; eye-ring dark red or orange.

Definitive Alternate Plumage. Eye-ring vermilion.

Legs And Feet

Hatchlings. Brownish black.

Juvenal Plumage. Dark bluish gray with pinkish overtones; webs pinker.

Basic I–Alternate III Plumages. Unchanged from Juvenal plumage.

Definitive Basic Plumage. Pale pinkish cinnamon or pink.

Definitive Alternate Plumage. Unchanged from Definitive Basic plumage.