Appearance

Figure 6. Annual cycle of breeding, migration, and molt in the Least Sandpiper.

Adult Least Sandpiper, breeding plumage; NY State, May

Adult Least Sandpiper, non-breeding plumage; California, December

Juvenile Least Sandpiper; NY State, August

Molts And Plumages

Hatchlings

Precocial and downy. Down whitish below, breast, neck, sides of head and forehead tinted buff or brownish. Facial marking variable; black streak from bill to eye; short malar streak. Dark marks on ear coverts. Pale around eyes; blackish crown tapering to base of bill. Sides of crown, hind crown (occiput) and nape orange buff with a little black mottling and 4 incomplete supraorbital lines of whitish down tips extending to occiput. Back and wings mottled black and yellowish to golden or chocolate brown. A diagonal cross or hour glass shape of white tipped “bottle-brush” down feathers on mid-back (Ticehurst 1930, Jehl 1968b). Barbs of bottle-brush down are intertwined for most of their length. Tips of barbs have short, white, densely packed barbules (Jehl 1968b, Fig. 14) which interlock with adjacent barbs forming the relatively discrete white plumage markings on downy young. Back pattern becomes diffuse or disappears in older chicks as bottle-brush feathers become worn or disentangled (Jehl 1968b).

Juvenal Plumage

Prejuvenal molt complete. Head: superciliary stripe relatively dull, especially behind eye, joining finely across forehead; split superciliary stripe (as found in Long-toed Stint) faint or lacking (Grant and Jonsson 1984); eye separated from dark patch on posterior ear coverts by faint paler area. Ground color of face dirty gray, not whitish. Loral region dark, broad and straight connecting the eyes and bill like a mask. Eyes appear somewhat oval rather than round. Crown and upperparts rather somber darkish browns, feathers margined buffy brown. Scapulars black, variably marked with reddish on bases, edged with buff and tipped whitish or creamy; mantle and scapulars edgings converge to form 2 striking “V” marks, on the mantle and scapulars respectively. Scapular “V” less conspicuous than mantle “V.” Wing coverts pale gray to blackish edged with buff to pale cinnamon/rufous; underparts whitish with light brown to pale buff neck and breast with speckling and streaking that is finer and less distinct than adults in Definitive Alternate plumage, and sometimes lacking in center of breast; tertials blackish, narrowly edged with rufous and patterned internally on some; rectrices predominantly ashy, central pair edged buffy brown; remiges more or less sepia with buffy-edged coverts (Palmer 1967, Grant and Jonsson 1984, Paulson 1993).

Basic I Plumage

Birds do not appear to molt prior to their first migration however, Maxwell (in Senner and Howe 1984) states that molt may be completed during migration at migratory staging areas in the central U.S. Birds wintering in California begin molt on the wintering grounds and undergo a partial molt of most body plumage, and a variable number of wing coverts, tertials (S10–S13) and rectrices from early Aug to early Dec. Replacement of tertials and rectrices varies from none to nearly all (Dwight 1900, Townsend 1927, Spaans 1976). Contrary to Cramp and Simmons (1983), no data exist regarding possible differences in extent of this molt among birds wintering in different areas (e.g. California vs. n. South America). Based on a misreading of Spaans (1976), Veit and Jonsson mistakenly state that this molt “is either partial or complete. [Birds] wintering in South America replace all flight feathers except some outer primaries and wing coverts between Sep and Nov.” In fact, young birds do not molt any flight feathers during this molt.

The color pattern of Juvenal S9 differs from that of S9 grown during subsequent molts. Juvenal S9 is largely black with a white tip. In later feather generations, the black extends along the rachis and “forms a small dark lanceolate marking into the white feather tip” (Burton and McNeil 1976). Because birds do not replace S9 during Prebasic I or Prealternate I molt (see below), this character is a reliable character by which to age birds.

Upperparts (including mantle, back, scapulars, secondary coverts, crown and nape) brownish gray, slightly darker feather centers (especially shafts) and paler feather edges create a somewhat mottled appearance. Rest of head off white with narrow darker streaks, dusky ear patch, dark lores, diffuse whitish supercilium and narrow whitish eye-ring. Breast slightly darker than remaining underparts and feathers with dusky streaks, creating a ‘breast band.’ Lower breast, belly and undertail coverts white. Tail pale brownish gray with darker inner feathers, outer upper tail coverts white, or with black shaft or center, central upper tail coverts blackish (Palmer 1967, Grant and Jonsson 1984, Veit and Jonsson 1984, Paulson 1993).

Alternate I Plumage

Prealternate I molt partial to incomplete; Jan–Jun, occurring mostly from Jan to mid-Apr, more extensive than Definitive Prealternate molt. Usually most body plumage (except some scapulars and upper wing coverts), some outer primaries (beginning between P5 and P8) and the innermost 2 or 3 tertials (S11–S13 or S12–S13) are replaced (Forbush 1925, Townsend 1927, Spaans 1976, Cramp and Simmons 1983). Timing may average about 1 mo later than Definitive Alternate molt (Forbush 1925).

Based on a misunderstanding of Spaans (1976), Cramp and Simmons (1983) and Prater et al. (1977) mistakenly state that this molt may be complete, beginning from early Nov to early Jan. In birds that replace outer primaries, Spaans (1976) found a negative correlation between primary molt score and body mass suggesting that molt is physiologically and energetically demanding.

Upperparts decidedly dark in tone, the feathers margined gray brown (not gray) to cinnamon/rufous on crown, auriculars, mantle and tertials; scapulars black with or without light brown to pale buff edges, and tipped whitish on some. Sides of head and much of neck white with dark (sepia/dusky) streaking; fairly conspicuous white supercilium and dark loral stripe; underparts white except breast light brown with conspicuous dark streaks. Marked demarcation between dark breast and whitish belly.

Lower back and inner rectrices black; outer upper tail coverts white or with black centers, central upper tail coverts black; rest of tail pale brownish gray. Wing brown above, narrow white wing stripe formed by moderately broad whitish tips of greater secondary coverts and quite narrow tips of greater primary coverts. Under wing and axillars white; greater primary coverts and tips of flight feathers gray brown; marginal coverts tipped darker brown (Palmer 1967, Veit and Jonsson 1984, Paulson 1993). Overall much variation in overall brightness (Paulson 1993).

Definitive Basic Plumage

Definitive Prebasic molt complete. Most to all molting occurs on the wintering grounds. Contrary to Cramp and Simmons (1983) no documented cases of birds arriving in n. South America with suspended flight feather molt (Spaans 1976). However, Maxwell (in Senner and Howe 1984) states that molt may be completed at migratory staging areas. Like other Calidris species timing of molt varies with length of migration. Short distance migrants wintering in California begin molt in Jul and complete flight feather molt by Oct and body molt by Nov (Page 1974). In contrast, birds wintering in n. South America begin molt in Aug or Sep and finish by Dec or early Jan (Townsend 1927, Spaans 1976, Cramp and Simmons 1983). Molt probably completed in some individuals in 130 d on Bolinas Lagoon, California with flight feather replacement in 72 d (Page 1974). Initiation of body molt precedes onset of flight feather molt (Dwight 1900, Page 1974). Primaries molt (proceeding from inner to outer) followed by secondaries (when inner 5–7 primaries replaced), and rectrices (after inner 3–5 primaries replaced). Secondaries replaced in sequence from outermost to S7 or S8, followed by S10 and then S9. Tertials molt in sequence from inner to outer. Recrtix molt begins with central pair and proceeds outward; however, in at least some cases, the outermost pair (R6) is replaced after the inner 2 or 3 pairs. In general rectrix molt more variable and asymmetrical than remigial molt (Page 1974, Spaans 1976). Timing of Definitive Prebasic molt of populations wintering in California coincides with timing of highest food densities (Page 1974).

Overall plumage color same as Basic I but some birds look plain while others more conspicuously streaked (Paulson 1993). Basic I plumage however, includes retained Juvenal flight feathers and some body plumage. These differences are imperceptible in the field and even difficult to detect in the hand.

Definitive Alternate Plumage

Definitive Prealternate molt incomplete; Jan–Jun. Includes head, neck, mantle, most scapulars, often some inner median upper wing coverts, some upper tail coverts, underparts, some to all tertials and usually their coverts, and 1–3 pairs of central rectrices (Forbush 1925, Townsend 1927, Page 1974, Spaans 1976, Cramp and Simmons 1983). Feathers replaced in Jan appear intermediate between Basic and Alternate plumage suggesting possible sex steroid hormonal regulation of plumage color in this species (Cramp and Simmons 1983).

Overall plumage color same as Alternate I. Alternate I plumage however, includes some to all retained Juvenal flight feathers and some Juvenal body plumage. These differences are imperceptible in the field and even difficult to detect in the hand.

Bare Parts

Bill

Blackish, short, and tapering to a fine point (noticeable at close range), with a distinct downward curvature in many but not all individuals (Paulson 1993).

Iris

Dark brownish.

Legs And Feet

Slaty in hatchlings. Yellowish green or gray green to occasionally brownish or olive in immatures (Wallace 1974). Variable, from dull to bright yellow (Paulson 1993) to greenish yellow (Palmer 1967) in adults. Legs short, toes longish.