Appearance

Plumage sequence well established (Glutz von Blotzheim and Bauer 1982, Cramp 1985, Wilds 1993, Olsen and Larsson 1995, Higgins and Davies 1996), but assignment of plumage stages to specific ages largely conjectural. Observation of wild known-aged birds suggests plumages of various ages vary more and overlap more than most publications indicate (ICTN).

Only detailed account of molt in American birds by Wilds (1993); primary molt also studied extensively in Europe, South Africa, and Australia (Walters 1979, Scott and Grant 1980, Underhill and Prys-Jones 1986, Craik 1994, Higgins and Davies 1996, Koopman 1996), but none of these studies included birds of known age. Blokpoel et al. (1984) studied a few known-aged birds in Trinidad. This account follows summary of molt schedules in Higgins and Davies 1996, but more study needed in the Americas.

Hatchlings

Covered in thick down. Upperparts, wings, and flanks cinnamon-brown to gray-brown, spotted or streaked with black, forming indistinct lines on back. Lores, sides of neck, and throat fuscous to brown-black; rest of underparts white. Rare type (about 2/1,000 at Bird I., MA; ICTN) has upperparts entirely pale cinnamon-buff, with spots only on head.

Juvenal Plumage

For development, see Cymborowski and Szulc-Olechowa 1966, Nisbet and Drury 1972 . Plumage usually complete by 25 d except for flight feathers; last down lost at about same time. Forehead and lores white, variably tinged light brown to gray-brown when fresh, fading to near white. Patch from front of eye, through ear-coverts, and around nape blackish, tinged or streaked brown when fresh. Rest of face and throat white. Crown light brown becoming dark brown distally, and more white and black with fading and wear. Hindneck and sides of head white. Back, scapulars, tertials, and most upper wing-coverts light gray, feathers variably tipped buff or light brown, scapulars and tertials with subterminal dark brown or cinnamon crescents or irregular bars, most prominent on largest feathers; becoming more uniform gray with wear and fading. Rump pale gray, grading to white upper tail-coverts. Underparts, under wing-coverts, and axillaries white, sometimes tinged buff on sides of breast. Tail pale gray, becoming dark gray on outer 2–3 feathers; all feathers tipped and margined on inner web with white. Dark carpal (cubital) bar formed by 3–4 rows of lesser upper secondary-coverts, mostly blackish gray with paler bases and narrow buff fringes. Alula and lesser primary-coverts dark gray fringed pale gray, often joining and extending carpal bar. Primaries medium neutral gray, lighter than in Definitive Basic plumage but with similar pattern of white central wedge and dark distal margin; tips and distal edges of all but outermost 3–4 white; secondaries dark gray with white inner margins and tips.

Basic I Plumage

Acquired by molt in Nov–Feb, except outer primaries molted Jan–Jul. When molt complete, like Definitive Basic except for darker outer webs to secondaries and dusky centers to tertials. Differs from adults by retention of some Juvenal markings into Dec–Jan; carpal bar wider and blacker; inner secondaries and outer primaries darker; outer secondaries and inner primaries lighter (fresh); tail less deeply forked. Also differs by retention of worn, faded outer primaries into Apr–Jun, when adults have fresh, whitish primaries.

Alternate I Plumage

Also known as portlandica plumage. Acquired by molt in May–Jun, except for primaries, which start to molt from innermost in Jun–Jul, overlapping first Prebasic molt of outermost. Like Definitive Basic except more white in tail (but less than Definitive Alternate), carpal bar reduced and said to be sometimes absent, primaries fresh in Jul–Aug; some have more black on forehead. Wilds (1993) stated that Alternate I plumage is missing in Common Terns and that there is only one molt, May–Jul, which she called pre-Basic II, but Higgins and Davies (1996) listed 2 molts and 2 plumages for birds in Australia. This needs clarification for American birds. Although birds in this plumage commonly observed in winter quarters during northern summer (Haverschmidt 1972, Higgins and Davies 1996) and are seen rarely (<2/1,000 adults; ICTN) at breeding colonies, no proof that these are all 1 yr old.

Basic II Plumage

Said to be acquired by molt in Jul–Sep (but see above), except for primaries. Second cycle of primary molt starts in Jun of second calendar year, and may continue through May of third calendar year. Like Definitive Basic, but said to have dark gray outer webs to secondaries and dusky centers to tertials, thus dark subterminal band on inner wing in flight (Wilds 1993); also differs in patterns of fresh and worn primaries (Higgins and Davies 1996), but this unconfirmed.

Alternate II Plumage

Sometimes referred to as pikei plumage. Acquired by molt in Feb–Jun, except primary molt starts Jan (overlapping second cycle) and may continue through Jul. Molt of head and body plumage incomplete (Wilds 1993). Forehead usually white, sometimes streaked blackish; forecrown white with scattered blackish streaks or blackish with scattered white streaks; crown dull blackish or brown-black. Carpal bar varies from dark to scattering of brown-black spots. Otherwise like Definitive Alternate except tail-streamers shorter and primaries (P7–P9) usually more worn, although outer primaries sometimes new by May (Wilds 1993). Cramp (1985) stated that some 2-yr-olds have all gray underparts and Olsen and Larsson (1995) stated that some are indistinguish-able from adults, but this requires confirmation.

Basic III And Definitive Basic Plumages

Acquired by complete molt Jul–Nov. Extent of head and body molt prior to southward migration variable, but some adults show white on forehead by Sep. Primary molt starts in Jul and is arrested before migration with 3–6 inner feathers replaced; completed Dec–Feb in winter quarters. Some start another cycle of primary molt by late Jan (Blokpoel et al. 1984). Forehead and lores white; crown white, variably streaked dark gray or black. Patch from front of eye through ear-coverts to hindcrown and around nape black or brown-black. Upper back, sides of neck and head below black patch, underparts, and axillaries white. Remainder of back, scapulars, tertials, and upper wing-coverts light gray. Lesser upper wing-coverts dark gray with indistinct whitish fringes when fresh, forming distinct carpal bar. Rump gray-white; upper tail-coverts gray-white with white bases showing when worn. Rectrices light gray with white inner webs, outermost rectrix pale gray on distal part of inner web and dark gray on outer web. Outer primaries pale silvery-gray on outer web, remainder of each feather black at tip and 60–90 mm along inner margin, with white shaft and white wedge running up inner web to 45–50 mm from tip; inner primaries and secondaries light gray with concealed white inner webs and narrow white tips. Inner 4–5 primaries and outer 2–3 secondaries translucent (Craik 1994).

Alternate III And Definitive Alternate Plumages

Acquired by complete molt Mar–May, except inner primaries and some outer secondaries molted Feb–Apr. Like Definitive Basic, but forehead and crown black or brownish black with variable white speckling, separated from gape by narrow white wedge. Back light gray (no white collar); rump and upper tail-coverts white; outer rectrices more elongated. Lesser upper wing-coverts pale gray (no carpal bar); leading edge of inner wing white. White tips to inner primaries and secondaries very narrow or absent. Most underparts pale gray, becoming paler with fading and wear, sometimes nearly white by Aug. Axillaries, under wing-coverts, and under tail-coverts white. Throat very pale gray, usually contrasting slightly with white face. Birds in Alternate III plumage (aged as 3 yr old by banding) usually have distinct white speckling on forehead, extending back above eye, sometimes distinct narrow white band above bill; some have traces of carpal bar, but most or all have entirely gray underparts; a few have little or no speckling on black cap and are indistinguishable from adults (ICTN). Four-year-olds usually have slight white speckling on forehead. A minority of older birds (of any age) have variable white speckling on cap; no clear evidence that speckling decreases or increases with age (ICTN). Similarly, birds of any age can have black cap tinged brown. Majority (61%) of breeding birds have 5 black outer primaries contrasting with gray inner primaries; about 25% have 4, 10% have 6, 3% have 3 and 0.4% have 7 (n = 501); no trends with age or sex (ICTN). When gray breast-feathers pulled, replacement feathers are white, even when grown in late May (ICTN).

Hatchlings

Iris dark brown. Bill pink with black tip. Legs and feet pink. In some, base of bill, legs and feet become orange-pink or dull orange by 12 d.

Juvenal

Iris dark brown. Bill pale flesh to pale yellow-orange at base of lower mandible; upper mandible and tip of lower mandible black, becoming mostly black with dull red-orange base by Sep. Inside of mouth dull orange. Legs and feet dull pale orange-pink.

Basic I, Alternate I And Basic II

Iris dark brown. Bill black. Legs and feet black, but sometimes dark red in Alternate I (Apr–Jul).

Alternate II

Iris dark brown. Bill with dull orange-red base and black tip; varies from mostly black to about half red. Legs and feet dull orange-red.

Definitive Basic And Definitive Alternate

In S. h. hirundo, iris dark brown. Bill mostly black, often with crimson-red at base of lower mandible and below nostril (nonbreeding) becoming red or orange-red, with 12–18 mm black tip, often with variable amount of black on culmen or sides of upper mandible (early breeding), two-thirds red (egg-laying), and largely red (late chick rearing in late Jul). Black begins to develop again in Aug, and by mid-Sep may be largely black or still largely red. Rarely bill has minute yellowish tip or is mostly black throughout breeding. Three- and 4-yr-olds have more black on bill than older adults at same dates (ICTN). Inside of mouth and tongue, orange. Legs and feet pale orange-red, dull red, reddish-brown, or reddish-black (nonbreeding) becoming bright vermilion-red (breeding); claws black. In S. h. longipennis bill all black throughout year; inside of mouth orange; legs and feet black (nonbreeding) to dull red or reddish-black (breeding); soles red (Higgins and Davies 1996).