Appearance

Sequence, timing, extent of molts, and plumage descriptions based on Cramp 1985 and Olsen and Larsson 1995, unless otherwise noted. Information has been obtained mainly from European populations; differences may exist between European and North American birds.

Hatchlings

In North American populations, two color morphs predominate: (1) dark type—light wood brown above, and (2) light type—pale creamy white above (San Francisco Bay, CA; DeGroot 1931, Miller 1943). Intermediate less common (San Francisco Bay, CA; Chaniot 1970). Underparts paler or white; lores and throat often gray. Dark morph has sooty throat-patch; lighter morph has white underparts (Miller 1943). Upperparts usually (but not always) spotted or mottled to some extent with dark freckling, and upperparts fade to almost white as young grow (Bent 1921).

Juvenal Plumage

Juvenal body plumage first appears on scapulars and back (Bent 1921). In 4 captive-reared chicks at Grays Harbor, WA: alar remiges and anterior portion of spinal tract begin developing at 10 d. At 24 d, spinal tract well developed and has mottled, washboard appearance; ventral tract white and well developed from base of lower mandible to tail. Rectrices merely stubs. Developing wing-coverts have mottled appearance. Down on head begins to be replaced by black cap starting at base of bill. At 34 d, black cap complete, though streaked with lighter colors on forehead and crown. Rectrices developing. At 41 d, feet beginning to turn from orange to black. Primary-tips just cross in back. At 48 d, primaries cross 2.54–3.81 cm. At 54 d, primaries and tail rectrices well developed (Penland 1976).

In European and North American populations forehead, lores, crown, and nape closely streaked pale buff or off-white and black, forming blackish cap. Upper mantle, scapulars, and tertials pale gray; feathers usually broadly edged with white (white portion partly tinged buff when fresh). Variable number of feathers have dull black or sepia subterminal V-marks on back and scapulars. In some, all upperparts marked; in others, marks often restricted to tertials or absent altogether. Back and rump as in Definitive Alternate plumage, but feather-tips often slightly tinged buff when fresh. Hindneck, underparts, axillaries, and underwing-coverts white.

Rectrices pale gray to nearly white, wide margins along tips and inner webs white; central 1–3 pairs often have dull black subterminal dots, others occasionally shaded dull gray subterminally, forming a dark band. Flight-feathers like those of adult, but gray is less silvery; inner edges and tips of inner 5–7 primaries and of primary-coverts bordered white, gray of feather-centers slightly darker subterminally; wedges to inner webs of primaries duller gray and indistinct. Upperwing-coverts like those of adult, but longer lesser-coverts and most median-coverts tinged off-white or buff at tips when fresh, shorter lesser-coverts slightly darker gray subterminally, forming indistinct carpal bar; some inner coverts occasionally have dull black subterminal mark (Cramp 1985).

Cap continues behind eye farther down onto sides of neck than in adult; juvenile has pale, narrow eye-ring that adult lacks (Olsen and Larsson 1995). In worn plumage, forehead and crown are paler and less heavily streaked black than in adult Definitive Basic plumage (Cramp 1985). Description of North American juveniles (Bent 1921) very similar to that of European juveniles.

Basic I Plumage

Prebasic I molt complete. In European and North American populations usually begins Sep–Dec on wintering grounds (sometimes earlier) and is complete by Mar–May (Bent 1921, Olsen and Larsson 1995), except for outer primaries, which often are not molted until Jun (Cramp 1985). Head, back, and most coverts molted first, followed by tertials, primary-coverts, and remiges. Primary molt pattern in immatures is usually different from rigid adult molt cycle. Primary molt begins Oct–Nov. As in other tern species, 2 or more waves of primary replacement occur during this molt, each wave beginning with innermost feather and proceeding sequentially outward. One to 4 inner primaries are molted Dec–Feb; 6–7 feathers molted Mar–Apr. Although primary molt can be completed May–Jun, normally not completed until Aug–Oct and usually suspended in summer. Next wave of replacement may begin Mar–Apr of second calendar year with inner primaries, thus 3 generations of primaries can be present. Plumage nearly indistinguishable from adult Definitive Basic when darkly patterned Juvenal upper mantle, scapulars, and tertials lost, but usually indistinct carpal bar persists, and Juvenal outer primaries are heavily worn and darker, contrasting sharply with paler inner feathers. This plumage also includes dark bar on secondaries, dark tail-feathers and dark primary-coverts, which Definitive Basic adult lacks.

In a captive-reared North American juvenile, mottled wing-coverts began to be replaced with pearly gray feathers at 41 d (Penland 1976).

Alternate I Plumage

Cramp (1985) reported that during spring and summer of second calendar year, no adult breeding plumage is attained in European populations. However, immature terns of other species undergo Prealternate molt during second calendar year, and adult Caspians have one in all subsequent years. Therefore it is possible that Prealternate molt occurs and simply results in a plumage identical to the previous one. Molt sequence in North American populations is probably similar to that of European populations.

Definitive Basic Plumage

Definitive Prebasic molt complete. In North America, usually begins with forehead and crown by Aug, but sometimes as early as Jun, before breeding season ends (Bent 1921). In European populations, molt begins with forehead and crown between late Jul and late Sep; primary replacement begins at same time and is suspended during migration, or begins after migration, and primaries are replaced from innermost outward. Body, tail, and wing molt completed Jan–Feb. After migration, rectrices replaced and primary molt begins again at point where previous primary molt was suspended. Inner 2–4 primaries are molted by about Mar, but birds completing Prebasic body molt late do not molt any flight-feathers. Molt of wing- and tail-feathers is suspended by the time breeding season begins. Primary molt does not resume again until after breeding, and begins with innermost feathers.

In birds assuming Definitive Basic plumage for the first time (fall of second calendar year), plumage very similar to adult, but tail-tips may still be dark. Subsequent immature molts are like those of adult, but cycles may be different; Prebasic may begin earlier or last longer, and Prealternate may involve greater number of inner primaries. Primary molt score may also be different from adult at same time of year, or when molt is arrested, some primaries often are relatively more worn than those of adult. (Cramp 1985).

In European populations, Definitive Basic plumage is similar to Definitive Alternate, except forehead, upper half of lores, and crown are heavily streaked black and white. Small patch below and in front of eye, as well as slightly elongated feathers of nape and ear-coverts, mostly black, feathers faintly fringed with white.

Definitive Alternate Plumage

Definitive Prealternate molt partial; in European populations, includes head and other body feathers and occurs Feb–Mar.

Forehead, upper half of lores, crown to just below eye, and slightly elongated feathers of nape black. Nape-feathers form short rough crest. Hindneck white. Mantle, scapulars, tertials, secondaries, and all upperwing-coverts pale gray; back pale gray, rump and uppertail-coverts white. Tail white, often with faint pale gray tinge. Outer webs of outer primaries and both webs of innermost are pale silvery gray; tips and inner webs of outer 5–6 primaries are blackish gray, and inner webs have ill-defined pale gray wedges toward bases; undersurface of outer feathers mostly dark gray. Underparts white, occasionally with slight gray tinge from lower throat to belly. Axillaries and underwing-coverts white. Silvery gray primary-tips become blackish with wear, especially on exposed parts; centers and outer webs of worn secondaries and tertials, and outer webs and tips of rectrices, become dark gray or brown-gray. Individuals with incomplete black caps are in summer of second or third calendar year. Whether incomplete caps are characteristic of all immatures is not known. In Least Terns, marked individuals of identical ages exhibited different Alternate plumages (Atwood and Massey 1982); thus, incomplete caps may occur in some but not all immature Caspians.

Definitive Alternate plumage acquired early and molted late; most individuals have black cap as early as Feb and retain it through autumn migration (Olsen and Larsson 1995).

Bill And Gape

In downy young, bill apricot orange, usually with black tip; becomes dull orange-yellow to orange-red in juvenile stage, tip extensively shaded horn-black. In breeding adults, bill bright coral red, extreme tip yellow, sometimes shaded brown subterminally. In nonbreeding adults, bill paler orange-red, 1–2 cm of tip horn-black (Cramp 1985).

Iris

Red-brown, sepia, or dark brown in adults; dark brown in downy young and juveniles (Cramp 1985).

Legs And Feet

In hatchlings, dark morphs have dark skin and dusky olive-colored feet; light morphs have light yellowish skin and dull orange feet (Miller 1943). In juveniles, yellowish foot develops blackish tinge, which gradually darkens to black foot of adult. Flesh of feet and legs is occasionally mottled or entirely orange-red, orange, or yellow in adults (FJC).