Plumages, Molts, and Structure

See Characteristics, above for sources; additional material from Johnson 1977a Johnson, O. W. (1977a). Plumage and molt in shorebirds summering at Enewetak Atoll. Auk 94:222-230. Close and Kinsky and Yaldwyn 1981 Kinsky, F. C., and J. C. Yaldwyn (1981). The bird fauna of Niue Island, south-west Pacific, with special notes on the White-tailed Tropic Bird and Golden Plover. National Museum of New Zealand Miscellaneous Series 2. Close . Capitalized color names follow Smithe 1975 Smithe, F. B. (1975). Naturalist's Color Guide. American Museum of Natural History, New York, NY, USA. Close with corresponding number codes given at first mention of each name; exception when referencing “brown” that often denotes several shades of this color and thus only numbers given. When match for a color not particularly close, number qualified with “c.” Plumage structure as follows: wings long and pointed; 11 primaries (rarely 12; Marks 1993 Marks, J. S. (1993). Molt of Bristle-thighed Curlews in the northwestern Hawaiian Islands. Auk 110:573-587. Close ), P10 longest, P11 minute; 16–17 secondaries, 4 alular feathers. Tail short, slightly rounded; 12 rectrices. Feathers of thighs with diagnostic narrow, elongated shafts (“bristles”) extending 25–50 mm beyond tip of webs. Adult found dead on Laysan I. 18 Aug 1991 had 6,081 contour feathers with dry mass of 23.45 g (Marks 1993 Marks, J. S. (1993). Molt of Bristle-thighed Curlews in the northwestern Hawaiian Islands. Auk 110:573-587. Close ).

Molt complex, as in other trans-Pacific migrant shorebirds (Johnson and Johnson 1983 Johnson, O. W., and P. M. Johnson (1983). Plumage-molt-age relationships in "over- summering" and migratory Lesser Golden-Plovers. Condor 85:406–419. Close , Marks 1993 Marks, J. S. (1993). Molt of Bristle-thighed Curlews in the northwestern Hawaiian Islands. Auk 110:573-587. Close , Gill et al. 2002a Gill, Jr., R. E., B. J. McCaffery and P. S. Tomkovich. (2002a). "Wandering Tattler (Heteroscelus incanus)." In The birds of North America, no. 642., edited by A. Poole and F. Gill. Philadelphia, PA: The Birds of North America, Inc. Close ). Plumage similar between sexes, but much individual variation. Following sequence of molts and their timing determined from birds in Northwestern Hawaiian Is. at northern end of winter range; unknown if sequences and timing similar farther south (Marks 1993 Marks, J. S. (1993). Molt of Bristle-thighed Curlews in the northwestern Hawaiian Islands. Auk 110:573-587. Close ). No evidence of molt while in Alaska (REG, BJM).

Hatchlings

Natal down well developed. Lower throat, sides of neck, and vent Pale Pinkish Buff (121D); upper breast, thighs, and central back whitish-buff. Upperparts with distinct blackish brown (Dusky Brown, 19) markings. See Allen and Kyllingstad 1949 Allen, A. A. and H. Kyllingstad. (1949). The eggs and young of the Bristle-thighed Curlew. Auk 66:343-350. Close for depiction of downy young.

Juvenile Plumage

Prejuvenile molt progresses rapidly, with chicks capable of sustained flight at 21–24 d after hatching (see Breeding: young birds, above). Juvenile plumage generally similar to breeding/nonbreeding adult but much warmer and more brightly patterned (contra Paulson 1993 Paulson, D. R. (1993). Shorebirds of the Pacific Northwest. University of Washington Press, Seattle, Washington, USA. Close ), especially 1–2 mo after fledging. Inner secondaries, scapulars, and wing coverts with large, cinnamon-buff (c. Salmon, 6) spots (= “notched” portion of feather; Paulson 1993 Paulson, D. R. (1993). Shorebirds of the Pacific Northwest. University of Washington Press, Seattle, Washington, USA. Close ). Juveniles arrive on wintering grounds in bright Juvenile plumage.

Basic I Plumage

Prebasic I molt complete, but timing extremely protracted. Molt begins with replacement of nonflight contour feathers late Sep to mid-Oct. Appearance virtually identical to that of Definitive Basic plumage except for prolonged retention of outer primaries and associated coverts, and some rectrices. Timing of replacement of rectrices highly variable, starting early Oct to mid-Nov, but sometimes not until second calendar year. Replacement of Juvenile primaries begins Mar–Jun of second calendar year (when birds 9–12 mo old), with secondary replacement occurring Jun–Sep. Primary molt completed late Jul–Oct when birds 13–16 mo old; latest completion dates result from retention of Juvenile primaries 9 and 10 (see below).

Alternate I Plumage

Appearance virtually identical to Basic, but little information on timing. Yearlings replace body feathers throughout summer of second calendar year, but very difficult to distinguish Pre-basic I from Prealternate I molts of nonflight contour feathers.

Basic II And Basic III Plumage

One-year-old birds begin replacing Basic I primaries in Jul and Aug when these feathers are new; some individuals retain Juvenile primaries 9 and 10, thus carrying 3 generations of primaries simultaneously (Marks 1993 Marks, J. S. (1993). Molt of Bristle-thighed Curlews in the northwestern Hawaiian Islands. Auk 110:573-587. Close ). Molt often incomplete so that birds in third calendar year possess fully grown Basic II and III primaries. Replacement of Basic I secondaries begins about halfway through primary molt. Replacement of Basic II primaries begins Jul–Aug and ends Oct–Nov, thus occurring about 1 mo ahead of adults that have migrated to and from breeding grounds. Exception is 32-mo-old bird on Laysan I. replacing Basic II P10 on 15 Feb (Marks 1993 Marks, J. S. (1993). Molt of Bristle-thighed Curlews in the northwestern Hawaiian Islands. Auk 110:573-587. Close ). Prebasic III molt occasionally incomplete based on 4 banded birds captured Feb to Apr of third calendar year with 2 generations of fully grown primaries. Differences in fading and wear between primary generations subtle and thus easily overlooked. Alternate II and Alternate III plumages virtually identical to corresponding Basic plumages. Subadults can be found replacing body feathers nearly year-round, so very difficult to distinguish Prealternate molts from corresponding Prebasic molts.

Definitive Basic Plumage

After Marks 1993 Marks, J. S. (1993). Molt of Bristle-thighed Curlews in the northwestern Hawaiian Islands. Auk 110:573-587. Close . Acquired with fourth and subsequent Prebasic molts and virtually identical in appearance to Definitive Alternate plumage (see below). Molt complete, beginning with nonflight contour feathers late Jul–late Aug soon after arrival on wintering grounds. Duration of primary molt averages 92 d, with mean start and completion dates of 2 Sep ± 1.7 d SE and 3 Dec ± 3.2 d SE, respectively (virtually all adults start replacing primaries by 5 Sep). Primaries 1–4 lost rapidly, followed by 2 or 3 more when first block about one-third grown; up to 7 primaries growing simultaneously on each wing, with average of 4 growing during early and middle stages of molt (molt scores 1–15 and 16–35, respectively) and 3 growing toward end (score 36–39). Outermost secondaries (S1–2) dropped first, usually after P1–6 have been dropped, followed by innermost (tertials), the molt waves con-verging between S9 and S12. Large blocks of secondaries dropped rapidly (see below) such that completion of secondary molt occurs shortly before or at about same time as that of primary molt. Rectrices not dropped until latter stages of secondary molt but highly variable with no discernible pattern.

Extent of primary and secondary loss causes flightlessness in some birds (Marks 1993 Marks, J. S. (1993). Molt of Bristle-thighed Curlews in the northwestern Hawaiian Islands. Auk 110:573-587. Close ), the only example of molt-induced flightlessness among extant shorebirds (Kinsky and Yaldwyn 1981 Kinsky, F. C., and J. C. Yaldwyn (1981). The bird fauna of Niue Island, south-west Pacific, with special notes on the White-tailed Tropic Bird and Golden Plover. National Museum of New Zealand Miscellaneous Series 2. Close , Marks et al. 1990 Marks, J. S., R. L. Redmond, P. Hendricks, R. B. Clapp and Jr. Gill, R. E. (1990). Notes on longevity and flightlessness in Bristle-thighed Curlews. Auk 107:779-781. Close ). Flightlessness results from either of 2 stages of remigial molt: (1) 4–7 inner and middle primaries dropped and/or no secondaries or 1–3 outer secondaries dropped (this type also missing most greater secondary wing coverts, leaving gaps between shafts of secondaries), and (2) 3–5 middle and distal primaries and large blocks of secondaries (6–14) dropped or growing simultaneously. Estimated 51% of adults on Laysan I. become flightless for at least 2 wk from Sep to Nov. Little known about extent of flightlessness south of Hawaiian Is. Curlew collected on Niue I. (east of Tonga) in the South Pacific 30 Nov 1963 was replacing all primaries on each wing and “must have been flightless at the time” (Kinsky and Yaldwyn 1981 Kinsky, F. C., and J. C. Yaldwyn (1981). The bird fauna of Niue Island, south-west Pacific, with special notes on the White-tailed Tropic Bird and Golden Plover. National Museum of New Zealand Miscellaneous Series 2. Close : 24), and a native of Rangiroa Atoll in the Tuamotu Archipelago noted that curlews were easier to catch in Oct when they were unable to fly (Marks et al. 1990 Marks, J. S., R. L. Redmond, P. Hendricks, R. B. Clapp and Jr. Gill, R. E. (1990). Notes on longevity and flightlessness in Bristle-thighed Curlews. Auk 107:779-781. Close , Gill and Redmond 1992 Gill, Jr., R. E. and R. L. Redmond. (1992). Distribution, numbers, and habitat of Bristle-thighed Curlews (Numenius tahitiensis) on Rangiroa Atoll. Notornis 39:17-26. Close ).

Definitive Alternate Plumage

Attained Jan–Apr from fourth and subsequent Prealternate molts. Molt incomplete, involving most body feathers and variable number of rectrices and perhaps lesser secondary wing coverts. General plumage well described but causes for variation, especially range in overall back-ground color, needs study. For example, multiyear observations of marked birds on breeding grounds (REG, BJM) suggest variation not age related; causes possibly region-specific diet and/or feather wear.

Head with narrow Buff (124) to Cream (54) median crown-stripe streaked brown (Fuscous, 21; Prout's Brown, 121A; Brussel's Brown 121B), extending from base of bill on forehead to rear of crown, but not to nape; bordered by broad dark to rich brown (21; Vandyke Brown, 121; 121A) lateral crown stripes from forehead to nape; these join across nape to form “U” shape; feathers on forehead with thin Buff fringes. Broad Buff supercilium with short, fine dark brown (121A/21) streaks. Lores brown (121) with small Buff streaks, forming thin, bold, dark loral-stripe that extends behind eye onto ear coverts. Rest of ear coverts Cream to Buff with short dark brown (121A/21) streaks; intensity of streaking varies greatly, possibly being more prominent in fresh plumage but varying individually. Chin and throat off-white to Cream. Front and sides of neck Pale Pinkish Buff, or Cream, with bold rich to dark brown (121; Raw Umber, 223; Verona Brown, 223B) shaft-streaks, the streaking more prominent than on ear coverts and becoming denser toward body. Hindneck brown (c. Raw Umber, 23) streaked with narrow cinnamon-buff (pale 6) edges; some birds appear less streaked on neck than others. Upperparts brown (Hair Brown, 119A to Sepia, 219) boldly spotted Buff to Pale Pinkish Buff, with much variation among individuals (REG). Mantle and scapulars brown (119A) with Pale Pinkish Buff corners (quite large, irregular spots) to feathers; some variation in Buff color within and between feathers; corners fade to Cream and reduced by wear and are sometimes worn away completely. Scapulars, brown (119A) with 2–3 large Pale Pinkish Buff tips, edges, or spots. Rump brown (119A) with cinnamon-buff (c. 6) edges or fringes to feathers forming untidy streaking. Upper tail-coverts cinnamon-buff to Pale Horn (92) or off-white; some feathers have varying brown (c. 121B) bars, chevrons, or streaks (or all 3) on webs, but these usually concealed or at least inconspicuous so uppertail coverts appear as broad, clean Buff patch. Breast variable from palest Cream (off-white) to deep Pale Pinkish Buff, with short, irregular wedge-shaped brown streaks (121B) in center of feathers, forming faint to prominent gorget ending abruptly above lower breast (though cutoff usually not conspicuous because streaking sparse); streaking may be heavier in fresh plumage. Feathers on sides of breast warm Buff to off-white with narrow brown (121B) shaft-streaks and partly exposed brown (121B) bases. Flanks Buff to off-white, irregularly barred with brown (121B) chevrons, mostly on inner webs; barring mostly concealed by closed wing. Axillaries broadly and evenly Pale Pinkish Buff and dark brown (121B). Lower breast, belly, and, to lesser extent, vent variable from off-white to pale cinnamon-buff. Thighs pale Buff with irregular brown (c. Mikado Brown, 121C) streaks mostly on inner webs and covering shaft distally; elongated shafts (bristles) shiny, almost transparent pale Buff. Undertail coverts uniform Buff or Pale Pinkish Buff. Tail Pale Pinkish Buff to cinnamon-buff (some paler) when fresh, with plain Buff tip and usually 6 complete dark brown (121) bars about 5 mm wide and 10 mm apart; basal 2 bars usually concealed by uppertail coverts. Central rectrices fade sooner than rest, quickly becoming pale Buff. Upperwing, including lesser- and median coverts dark brown (121, 119A) with broad, irregular Pale Pinkish Buff edges or fringes, slightly paler than upperparts; edges of median coverts and posterior lesser coverts worn and faded to Cream or off-white by arrival of birds on breeding grounds, giving very contrasting light area to folded wing (REG). Greater secondary coverts dark brown (121) with large, bold Pale Pinkish Buff lateral spots on both webs. Greater primary coverts dark brown (121) with broad white to Buff tips on inner ones. Outer 4 primaries (P7–P10) appear unbarred from above and are dark brown (219) with pale Buff lateral notches along inner webs (7 mm wide, 5 mm apart); form broad, sharply defined bars, extending half to two-thirds the width of inner web and not reaching shaft, widest at edge, narrower and rounded toward shaft (Higgins and Davies 1996 Higgins, P. J., and S. J. J. F. Davies (editors). (1996). Handbook of Australian, New Zealand & Antarctic birds. Volume 3. Melbourne: Oxford University Press. Close , specimens). Others describe marking on outer primaries as diffuse mottling (Mlodinow et al. 1999 Mlodinow, S. G., S. Feldstein and B. Tweit. (1999). The Bristle-thighed Curlew landfall of 1998: climatic factors and notes on identification. Western Birds 30:133-155. Close ) or being un-notched (Paulson 1993 Paulson, D. R. (1993). Shorebirds of the Pacific Northwest. University of Washington Press, Seattle, Washington, USA. Close ); this often the case in subadults, but almost all breeding adults with prominently notched outer primaries (REG, BJM; photo Kyllingstad 1948 Kyllingstad, H. C. (1948). The secret of the Bristle-thighed Curlew. Arctic 1:113-118. Close ). P6 similar to outer primaries but with narrow Buff fringe at tip and with smaller Buff spots along outer edge. Inner 5 primaries appear barred above; dark brown (219), fading to brown (119A) with wear, with about 5 bold, sharply defined Buff to Cream spots on outer webs (5–7 mm wide, 7–8 mm apart), about two-thirds width of webs; similar spots on inner web shorter, less well defined, and paler buff-gray; broad Buff tips grade to Cream distally. Secondaries gray-brown (c. Grayish Horn, 91) with distinct buff-gray spots on both webs, less boldly barred than inner primaries. Inner secondaries (tertials) dark brown (121/119A) with bold cinnamon-brown (c. 6) spots prone to wear and sometimes lost. On underwing, primaries bold gray-brown (c. Olive-Brown, 28) with Buff tips and lateral spots and bold brown (121) barring with barring about twice the width of the notching (on underwing of N. p. hudsonicus Whimbrel notching of outer 7 primaries about twice the width of barring; REG). Secondaries appear duller, buff-gray, with bold gray-brown (91/28) barring and Buff notching (barring broader than notching); Buff tip to inner web forms narrow, pale trailing edge. Greater underwing primary coverts Olive-Brown with Buff tips and lateral spots. Greater underwing secondary coverts and subhumerals dark brown (121) boldly barred cinnamon-buff (c. 6). Lesser- and median coverts dark brown (121) spotted deep cinnamon-brown (c. 6). In flight, wing lining appears dark brown closely barred pink-buff to cinnamon-buff (c. 60% brown, 40% buff) and contrasts sharply with buff-gray of rest of underwing.

Bill And Gape

Bill ranges from entirely black to bicolored, with basal three-fourths or more of lower mandible (sometimes including base of upper mandible; see Rosair and Cottridge [Rosair and Cottridge 1995 Rosair, D., and D. Cottridge (1995). Hamlyn Photographic Guide to the Waders of the World. Hamlyn Limited, Melbourne, Australia. Close ]) brown/dusky pink to pink; color darkens distally. Occasionally, just tomia with pink. Among 7 breeding pairs observed upon arrival (May) at Curlew Lake, 6 females with dramatically more pale on lower mandible than mates; however in 1 pair, female with all dark bill and male with pale on lower mandible (BJM). Between members of pairs in hand during early stage of hatching at Neva Creek (n = 27 pairs), males always with less and duller pink on basal lower mandible, ranging from no pink or slightly pink (often discernible only in hand) to pink over one-third of mandible. Females usually with brighter and more extensive coloration that frequently extends throughout proximal half of lower mandible (REG). Bill color changes seasonally (less black in winter) and possibly with age class; more study needed (REG, JSM).

Iris

Dark brown to blackish.

Legs And Feet

Four downy young described as “cadet gray” (Allen and Kyllingstad 1949 Allen, A. A. and H. Kyllingstad. (1949). The eggs and young of the Bristle-thighed Curlew. Auk 66:343-350. Close ); adult light blue-gray or grayish blue.

See Appendix 1 . Females significantly larger than males for all measurements recorded. Body mass highly variable among seasons owing to premigratory fattening.