Plumages, Molts, and Structure

Hatchlings

Head and upperparts buff with gray down-bases showing through. Black spots on crown arranged in irregular bars or a distinct ring around crown. Three more-or-less concealed black bars on back of nape, and short black marks on back form bar or several short stripes in interscapular region and diamond-shaped patterns on lower back. Small dark spot behind eye, but side of head otherwise unspotted. Chin and throat golden buff, remaining underparts whitish or buffish gray (Cramp and Simmons 1983 Cramp, S., and K. E. L. Simmons (1983). The Birds of the Western Palearctic, Volume 3: Waders to Gulls. Oxford University Press, Oxford, UK. Close ). General coloration of down and amount of spotting variable (Fjeldså 1977 Fjeldså, J. (1977). Guide to the Young of European Precocial Birds. Skarv Nature Publication, Tisvildeleje, Denmark. Close ), some individuals having more spotting on sides of head and a spot above base of bill. Hatchlings similar to, but darker than, those of Common Terns (DVW). Unlike some Laridae, hatchlings not known to occur in different color morphs.

Juvenile Plumage

Head white, with brown-black crown, upper nape, lower band on cheek and crescentic mark in front of eye and some feathering around eye. Narrow white area on hindneck. Base of hindneck, upper mantle and sides of chest black, feathers tipped narrowly with yellow-buff, gray, or white. Feathers of mantle, back, and scapulars blackish brown with whitish fringes giving scaly pattern, most prominent on scapulars. Back and upper rump gray, barred blackish brown. Lower rump and uppertail-coverts white, tipped grayish-brown. Underparts, including axillaries and entire underwing surface, white. Tail white with broad subterminal brown-black band. Outer feathers with less black, and outermost with no black, or with small patch at tip of inner web. On upper surface of wing, P10–P8 brown-black with outer part of inner web white except at tip. P7–P6 similar but rest of inner web, along shaft, paler and grayer. P5 similar but white of inner web more extensive, almost reaching shaft near tip and with gray tongue on outer web (sometimes also on P7–P6). P4–P1 white with area along shaft and outer edge of outer web dark brown-gray, and rest of outer web and inner part of inner web pale gray. P4 (and rarely P3) with small brown-black spot on outer web near tip. Secondaries white with black shaft-streak or drop-shaped, brown-gray to brown-black mark along shaft, elongated on outer web and shorter (confined to distal part of feathers) on inner web. Marks become progressively narrower, darker, and sharper proximally along wing, then larger again on tertials to occupy most visible part of feather except for narrow edge. Primary-coverts brown-black, narrowly tipped white, innermost pale gray with pale brown shaft-streaks. Greater-coverts pale gray, with inner webs and tips white, sometimes with dark shading on base of inner web. Tertials dark brown, with narrow white margins. Median-coverts and larger lesser coverts black-brown, narrowly tipped pale buff or white. Smaller lesser coverts broadly fringed gray-white, with bases black-brown. Alula and coverts along outer edge of outer primaries brown-black, with outer webs white.

Basic I Plumage

Head white with dark gray or blackish eye-crescent, ear spot and crown. Hindneck, mantle, back and scapulars pale gray, often with a few Juvenile feathers retained on back and scapulars. Remaining upperparts, including upperwing, as Juvenile plumage, giving distinctive M-shaped dark pattern to upperwings in flight, very distinct from uniform pale gray upperwing of Definitive Basic plumage. Black area at base of hindneck or upper mantle and sides of chest often retained longer than rest of Juvenile mantle and scapular feathers, giving distinct collared appearance. Sides of breast pale gray. Other underparts like Definitive Basic plumage. Central 1–4 pairs of tail feathers usually as in Juvenile plumage, but sometimes replaced by white ones. Tips of other tail feathers and remiges progressively reduced by abrasion.

Alternate I Plumage

Head and neck resemble Definitive Basic plumage, but often with variable number of brown-black feathers, occasionally head dark sooty brown or black with or without white forehead (Cramp and Simmons 1983 Cramp, S., and K. E. L. Simmons (1983). The Birds of the Western Palearctic, Volume 3: Waders to Gulls. Oxford University Press, Oxford, UK. Close ). Upperparts, including all scapulars, like Definitive Basic plumage, but remiges and rectrices retained from Juvenile plumage, and wing coverts progressively replaced (precise chronology unclear) by gray ones. Variable numbers of tail feathers white by this stage. Occasionally birds acquire pink flush on underparts (as in Definitive Alternate plumage), and lose gray sides to breast. Wings become very worn and faded by late summer, and dark areas such as carpal bar often fade to pale brown.

Basic Ii Plumage

Similar to Definitive Basic plumage, but upper surface of P10 with outer web black or gray-black, P9–P6 with black subterminal marks, bands, spots, or shaft-streaks, dark shading on inner web of primaries and secondaries reduced or lacking, underwing coverts paler or white, axillaries white, median and lesser underwing coverts whitish or gray, contrasting with grayish remainder of underwing (underwing thus never as uniformly and dark black as in Definitive plumage). Occasionally, alula, marginal underwing coverts, inner secondaries, and tertials have small blackish-brown marks.

Alternate Ii Plumage

Differs from Definitive Alternate plumage only by dark outer web of P10 and sometimes by paler gray underwing, especially greater, median, and lesser undersecondary coverts (Veen 1980 Veen, J. (1980). Breeding behaviour and breeding success of a colony of Little Gulls Larus minutus in the Netherlands. Limosa 53:73-83. Close , Grant 1982c Grant, P. J. (1982c). Gulls: a guide to field identification. Vermillion, SD: Buteo Books. Close ).

Definitive Basic Plumage

Head white, with dark gray-black crescent in front of eye. Rear of crown and nape dark gray, black ear spot, slight black feathering often around eye, with usually a streaked, dark gray-and-white band from eye to ear coverts, and sometimes a few dark edges on forecrown feathers. Hindneck upper mantle and sides of chest white. Mantle, scapulars, and back pale blue-gray, scapulars tipped white. Rump, uppertail-coverts, tail, and underparts white. Underparts sometimes flushed pink, but rarely as intense as in Definitive Alternate plumage. Primaries pale blue-gray shading to lead-gray on inner half of inner web, with broad white tip and white edge on distal inner web of all except P9–P10. Secondaries pale blue-gray with dark shading on inner web, broad white tip, and white edge on outer web. Tertials and all upperwing coverts pale blue-gray. Thus, upperwing appears gray with white border on trailing edge and tip. Underside of remiges blackish, and underwing coverts lead-gray or blackish. Axillaries ash-gray. Occasionally birds in third year (i.e., Basic III plumage) still show dark outer web of P10 and paler underwing than in older adult.

Definitive Alternate Plumage

Plumage as Definitive Basic but with black hood, extending over whole head and upper neck. Hood sometimes molted in Jul if failed breeder, with a few black feathers sometimes remaining into Oct (Cramp and Simmons 1983 Cramp, S., and K. E. L. Simmons (1983). The Birds of the Western Palearctic, Volume 3: Waders to Gulls. Oxford University Press, Oxford, UK. Close ). Entire underparts, hindneck, and mantle often suffused with pink, especially obvious on breast.

Figure 4 . No studies specific to North America, but specimens and field observations indicate general appearance of North American birds similar at all life stages to those described for Palearctic by Tinbergen (Tinbergen 1937 Tinbergen, L. (1937). Feldbeobachtungen au Zwergmowen, Larus minutus Pall. Limosa 10:12-21. Close ), Veen (Veen 1980 Veen, J. (1980). Breeding behaviour and breeding success of a colony of Little Gulls Larus minutus in the Netherlands. Limosa 53:73-83. Close ), Grant (Grant 1982c Grant, P. J. (1982c). Gulls: a guide to field identification. Vermillion, SD: Buteo Books. Close ), and Cramp and Simmons (Cramp and Simmons 1983 Cramp, S., and K. E. L. Simmons (1983). The Birds of the Western Palearctic, Volume 3: Waders to Gulls. Oxford University Press, Oxford, UK. Close ). No known sex differences in molt or plumages. Following descriptions of molt and plumages based on Palearctic birds unless indicated otherwise.

Prejuvenile Molt

Timing and sequence of feather emergence in Prejuvenile molt unclear and little studied.

Prebasic I Molt

Acquired by partial (but sometimes incomplete) Prebasic I molt of head and other body feathers, which begins at fledging and is usually complete by Nov in the Palearctic (Grant 1982c Grant, P. J. (1982c). Gulls: a guide to field identification. Vermillion, SD: Buteo Books. Close ). Molt does not include remiges, but occasionally some central rectrices molt.

Prealternate I Molt

Prealternate I molt incomplete; includes head, body, and some inner upperwing coverts; occurs Feb–May in Palearctic (Grant 1982c Grant, P. J. (1982c). Gulls: a guide to field identification. Vermillion, SD: Buteo Books. Close ).

Preasic II Molt

Acquired by complete Prebasic II molt, in Jun–Oct in Palearctic, but between Jun and Aug in Ontario (PJE, DVW).

Prealternate II Molt

Prealternate II molt partial; includes head and body feathers; occurs Feb–May in Palearctic.

Definitive Prebasic Molt

Acquired by complete Definitive Prebasic molt in Jun–Nov (Palearctic) and probably similar period in North America.

Definitive Prealternate Molt

Definitive Prealternate molt partial; includes head and body feathers; occurs Jan–May (Palearctic), and probably Mar–Apr in North America, but little information available.

Bill And Gape

Downy chicks have flesh-pink bill with dark brown tip. Gape flesh-pink in juveniles, bright orange or red thereafter, color more intense in older birds. Bill dark brown-black in full-grown birds, often tinged red in breeding adults, especially at base.

Iris

Dark brown or black at all ages. Orbital ring red in Alternate plumage at least (Cramp and Simmons 1983 Cramp, S., and K. E. L. Simmons (1983). The Birds of the Western Palearctic, Volume 3: Waders to Gulls. Oxford University Press, Oxford, UK. Close ), but described as blackish-brown by Grant (Grant 1982c Grant, P. J. (1982c). Gulls: a guide to field identification. Vermillion, SD: Buteo Books. Close ) in Basic-plumaged birds. Orbital ring blackish in Juvenile plumage (Grant 1982c Grant, P. J. (1982c). Gulls: a guide to field identification. Vermillion, SD: Buteo Books. Close ).

Legs And Feet

Flesh-pink, sometimes washed gray-brown, in juveniles and immatures, becoming orange to vermilion red in adults. Webs usually darker than leg. Claws black–dark brown.

Measurements made by the authors. Based on specimens collected mostly in Great Lakes region, also Connecticut (2) and Texas (1). Males average slightly larger than females (see also Veen 1980 Veen, J. (1980). Breeding behaviour and breeding success of a colony of Little Gulls Larus minutus in the Netherlands. Limosa 53:73-83. Close , Cramp and Simmons 1983 Cramp, S., and K. E. L. Simmons (1983). The Birds of the Western Palearctic, Volume 3: Waders to Gulls. Oxford University Press, Oxford, UK. Close ), but North American sample sizes small. Immatures (1 male and 3 females) average smaller than adults on all measurements except culmen.

Linear Measurements

See Table 2 for culmen, wing, tail, and tarsus of North American specimens. Bill depth at angles of gonys: for adult males, mean 5.6 mm ± 0.3 SD (range 5.3-6.0, n = 4); for 1 adult female, 5.2 mm.

Mass

Mass at collection of North American specimens (mostly outside the breeding season): Adult males, mean 116.1 g ± 10.9 SD (range 99.2-125.0, n = 6); one adult female, 134.5 g. An unsexed adult in Dec weighed 155.5 g. In the Netherlands and Belgium (presumably during the breeding season) 8 adult males averaged 99 g (range 82-117); 4 adult females averaged 98 g (range 93-108; Cramp and Simmons 1983 Cramp, S., and K. E. L. Simmons (1983). The Birds of the Western Palearctic, Volume 3: Waders to Gulls. Oxford University Press, Oxford, UK. Close ). Two immature females in North America, Jun, weighed 110 g and 120 g. In Palearctic, immatures averaged lower mass than adults, but precise collection dates unclear. No marked sexual dimorphism noted in Palearctic specimens (Cramp and Simmons 1983 Cramp, S., and K. E. L. Simmons (1983). The Birds of the Western Palearctic, Volume 3: Waders to Gulls. Oxford University Press, Oxford, UK. Close ).