American Oystercatcher Working Group

Appearance

Author: Sara Schweitzer (SHS), North Carolina Wildlife Resources Commission, Raleigh, NC.

Appearance

American Oystercatchers have 10 functional primaries, 16-17 secondaries (including 4 tertials), and 12 rectrices; oystercatchers are diastataxic (see Bostwick and Brady 2002) indicating that a secondary has been lost evolutionarily between what we now term s4 and s5. Wings are moderately rounded, tail is short and squared, and bill and legs are stout and strong. Geographic variation in appearance moderate. The following molt and plumage descriptions pertain to the nominate North American subspecies; see Systematics: Geographic Variation for appearance variation in up to four other recognized subspecies in Mexico through South America. No geographic and little or no sex-specific variation in molt strategies reported, although variation in timing and extent likely in temperate vs. tropical populations due to variable environmental constraints, day-length regimes, and breeding seasonality; molt in South American populations undoubtedly differs in timing, at least, from that described below.

Molts

Molt and plumage terminology follows Humphrey and Parkes (1959) as modified by Howell et al. (2003, 2004). American Oystercatcher reported to exhibit a Complex Basic Strategy (cf. Howell et al. 2003, Howell 2010), including complete prebasic molts and a partial preformative molt but no prealternate molts (Dwight 1900, Bent 1929, Webster 1942, Palmer 1967a, Oberholser 1974, Prater et al. 1977, Pyle 2008; Fig. 3), but no detailed qualitative or quantitative studies of the sequence, timing, and extent of molt have been conducted.  It has been assumed that the sequence and extent of molts of the American Oystercatcher were similar to those of the European Oystercatcher (Dare and Mercer 1974, Pienkowski and Knight 1975, Boere 1976, Hulscher 1977, Wilson and Morrison 1981, Cramp and Simmons 1983, Koopman 1992) because many authorities deem them closely related (Peters 1934, Murphy 1936, Hellmayr and Conover 1948, Heppleston 1973b, Sibley and Monroe 1990), but the timing and location (breeding grounds, migratory staging area, wintering sites) of molts are plastic in birds (P. Pyle, pers. comm.), and could differ substantially between the two oystercatcher species. Furthermore, European Oystercatcher has a Prealternate Molt in adults which has not been reported in American Oystercatcher (see also Webster 1942); if the same were to occur in American Oystercatcher it would exhibit the Simple Alternate Strategy (Howell et al. 2003, Howell 2010). Molts of North American populations follow a “Northern Hemisphere Strategy” as defined by Pyle (2008), which generally includes accelerated and partial preformative molts and accelerated prebasic molts (to complete before onset of winter) as compared to species that migrate to the Southern Hemisphere for the non-breeding season.

Prejuvenal (First Prebasic) Molt

Complete, Jun-Aug in North America, on or near the breeding territory. We assume development of this plumage is similar to that of the Black Oystercatcher of w. North America, described by Webster (1942), as follows:  By 12 d, Juvenal plumage develops on flanks and along ventral midline; primaries pierce skin.  Between 14 and 21 d, Juvenal secondaries, secondary coverts, rectrices, auriculars, and crown feathers appear (Figs. 5, 6, 7, 8).  Down remains attached to tips of Juvenal feathers, especially on rump (Fig. 9), underside of neck, flanks, and legs. Juvenal plumage is fully developed by 6 wk, and last traces of down (usually on inner thighs) disappear thereafter.

Preformative Molt

“First Prebasic” or “Prebasic I” Molt according to Humphrey and Parkes (1959) and some later authors; see revision by Howell et al. (2003).  Limited to incomplete, Sep-Dec in North America (Fig. 5), on or near breeding grounds. Includes some to most body feathers, no to a few proximal secondary coverts, sometimes 1-3 tertials, and often 1-2 central rectrices (r1), occasionally to all rectrices, but no primaries, primary coverts, or secondaries other than tertials (Pyle 2008).

First and Definitive Prealternate Molts

Reported not to exist in this species (see above). In European Oystercatcher a limited Definitive Prealternate Molt occurs, involving some to most head and throat feathers (Cramp and Simmons 1983); study needed on whether or not a limited Definitive Prealternate Molt may occur in some American Oystercatchers, or if a First Prealternate Molt occurs in either species.

Definitive Prebasic Molt

Incomplete to complete, Apr-Dec in North America (Fig. 5), occurring primarily on or near breeding grounds but probably can complete on non-breeding grounds in migratory populations. Second Prebasic Molt and later molts of non-breeding individuals can commence a month or more earlier (Apr or May) as compared to those of successful breeders.  Among successful breeders, females probably begin molt later than males (Webster 1942, Dare and Mercer 1974, Wilson and Morrison 1981); molt can commence during incubation and suspend for chick feeding (after 1-3 inner primaries, at least, replaced) and this may occur more frequently in females than males, as in raptors with similar suspended molts (Pyle 2008).  Primaries replaced distally (p1 to p10), secondaries replaced proximally from s1 and s5 and distally from the tertials, and rectrices probably replaced distally (r1 to r6) on each side of tail, with some variation in rectrix sequence possible. Usually complete but 1-3 secondaries (among s7-s12, the last feathers replaced) can occasionally be retained during incomplete molts.

Plumages

Following based primarily on detailed plumage descriptions in Ridgway (1919), Bent (1929), Murphy (1936), Webster (1943), Palmer (1967b), Oberholser (1974), Paulson (2005), and O’Brien et al. (2006); see Prater et al. (1977) and Pyle (2008) for specific age-related criteria. Sexes similar in all plumages. Definitive Plumage typically assumed at Second Basic Plumage. Throughout this section, capitalized names and colors refer to those in Smithe (1975) unless specified otherwise.

Natal Down

Present primarily May-Aug in North America. Dark grayish chin, throat, and breast, clearly demarcated (as in adults) from remainder of entirely white underparts. Dark breast sometimes extends dorsally to form a collar around the nape that is darker than adjacent head and back plumage.  A narrow black stripe runs from the base of the bill through each eye to the nape. Two parallel black stripes down back; a black dot behind eye (Figs. 1, 2). A black stripe on each side of body from base of tail (top of femur) to wing (shoulder) separates darker dorsal down from light ventral down (Fig. 3). Otherwise, upperparts Drab (color 27) with rump and flanks tipped with Buff (color 124) to Warm Buff (color 118; Fig. 3). Auriculars and areas above and below eyes, light Buffy Drab (Avellaneous of Ridgway 1912); sides and back of neck uniformly Light Drab (color 119c; photos in Bancroft 1927, Tomkins 1954, Hall 1960; line drawing and photo in Jehl 1968; color plate in Harrison 1978; Fig. 4).

Juvenal (First Basic) Plumage

Present primarily Jun-Oct in North American populations. Back, scapulars and wing coverts light Raw Umber (color 223), tipped with Clay to Cinnamon color (colors 123b and 123A, respectively; Fig. 6, 7); crown, sides of head, and chest Raw Umber (color 223) tipped with Cinnamon (color 123A); chin and throat mottled Fuscous (color 21) to buff;  whitish feathers around base of bill (Figs. 10, 13); uppertail coverts white tipped with buff (Fig. 9); rest of underparts white.  Tail Raw Umber (color 223) distally, tipped with Cinnamon (color 123A), and white basally, the rectrices with indistinct demarcation between light and dark (illustrated by Pyle 2008); wing feathers Raw Umber (color 223) with white wing bar consisting of greater upper secondary coverts, widest in the middle and tapering both distally and proximally (Figs. 11, 12).  By end of Jul, lighter colored feather tips often become bleached and nearly gone due to wear.

Formative Plumage

“First Basic” or “Basic I” plumage according to Humphrey and Parkes (1959) and later authors; see revision by Howell et al. (2003). Present primarily Oct-Sep in North American populations. Head and neck Fuscous (color 21) or Sepia (color 119); mantle Dark Neutral Gray (color 83); underparts white.  Similar to Definitive Basic Plumage except for retained juvenal scapulars, most wing coverts (which can be tipped whitish when fresher), and rectrices paler and duller in color, forming contrasts with newer and darker, replaced formative back feathers, proximal wing coverts, and 1-3 tertials. Some to most rectrices usually retained, the juvenal feathers contrastingly narrow and with less distinct demarcation between white bases and dark tips (Pyle 2008).

First and Definitive Alternate Plumages

May not exist (see Prealternate Molts); but if so, similar to Formative and Definitive Basic plumages, respectively, but some head and neck feathers replaced, contrastingly fresh. Coloration of feathers would appear to be identical, unlike in European Oystercatcher, in which white neck and chin feathers of Basic Plumage replaced with dark feathers.

Definitive Basic Plumage

Present primarily Oct-Sep in North American populations.  Head, neck, and upper chest uniformly black with faint bluish green gloss; white streak immediately below lower eyelid; back, scapulars, rump, and anterior median uppertail coverts plain grayish brown or brownish gray (similar to colors 119A and 119B); median anterior uppertail coverts sometimes edged white; lateral and posterior uppertail coverts white, the latter rarely with a few dusky spots or blotches.  Lower chest, belly, undertail coverts, axillars, and underwing coverts white, the underwing coverts sometimes tipped with brownish gray, and the carpometacarpal region (wrist) spotted dusky.  Inner primaries (p1-p4, less frequently p5, p5-p6, or p5-p7) with basal white areas, usually 25 mm or more in length, on their shafts and outer webs.  Tips of upperwing median coverts, all exposed portions of greater coverts, and secondaries immediately distal to tertials immaculate white.  More distal secondaries deep brownish gray  with white on inner webs and basal part and distal edges of outer webs. Primaries and primary coverts dull black. Tail deep brownish gray becoming darker (sometimes nearly black) distally and white basally, the demarcation between white and dark of rectrices distinct (illustrated by Pyle 2008).  Upperpart feathers, wing coverts, tertials, and rectrices all uniform in wear (all Basic), not showing molt limits as in Formative Plumage.

Bill

Fledgling bill mixture of grays and buffs (Fig. 13), becoming pale orange with dusky at extreme tip by 12 mo (Cadman 1980), and relatively dull red without yellow tip through second year (illustrated by Pyle 2008).  Adult bill vermillion with yellowish tip and scarlet red base (Fig. 14).

Iris

Brown in fledglings (Fig. 13), becoming pale lemon-yellow by 12 mo and lemon yellow in adults (Fig. 14).

Orbital Ring

Brown in chicks (Figs. 4, 5, 8, 10), dark brown-orange in fledglings (Fig. 13), and chrome orange in adults (Fig. 14).

Legs

Dull grayish in fledglings, becoming gray by 12 mo, and pinkish-white in adults.


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