Pacific Golden-Plover Pluvialis fulva Scientific name definitions
Version: 1.1 — Published April 15, 2021
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23–26 cm; 100–228 g; wingspan 60–72 cm. Black underparts with narrow white line along flanks in summer plumage; vent tends to be mostly white with scattering of black. Has longer legs and is yellower than European Golden Plover (Pluvialis apricaria), with brownish-gray underwing, and wings clearly longer than tail. Various features suggested for separation of formerly conspecific American Golden-Plover (Pluvialis dominica) from present species, but perhaps only three are valid: the number of primaries exposed beyond the longest tertial (2–3 in Pacific Golden-Plover, 4–5 in American Golden-Plover), primary projection past the tail-end (c. 0–9 mm in Pacific Golden-Plover, 12–22 mm in American Golden-Plover), and breeding plumage; in some cases, involving molting birds and those in non-breeding plumage, unequivocal species identification may be impossible (2, 3, 4, 5, 6, 7). Female somewhat less black than male . Non-breeding adult has yellowish-buff breast, grading to whitish on belly and vent; golden spotting less prominent. Juvenile as non-breeding adult, but has brown barring on flanks. One report of aberrant white plumage (8).
A medium-sized plover that is very similar in appearance to American Golden-Plover. Ranges of all standard measurements overlap between the two species (see 9). The following features helpful, but not infallible, in separating the species: length of Pacific Golden-Plover (23–26 cm) is frequently less than American Golden-Plover (24–28 cm); flattened wing in Pacific Golden-Plover is typically < 175 mm and in American Golden-Plover is > 180 mm; Pacific Golden-Plover tends to have slightly longer bill and tarsus, and tibia more exposed and less feathered proximally, giving the species a somewhat longer-legged appearance than American Golden-Plover; in all plumages, Pacific Golden-Plover upperparts are spangled with bright yellow markings on dark grayish-brown background, American Golden-Plover upperparts are similar but less colorful. The most reliable field criteria for identifying the two species (9) are: interspecific differences in alternate plumages during spring and part of the summer; extension of primary feather tips beyond the longest tertials on folded wing, typically 2–3 tips in Pacific Golden-Plover, 4–5 tips in American Golden-Plover (although beware of molting or growing tertials); and primary tip projection past end of the tail (0–9 mm in Pacific Golden-Plover, 12–22 mm American Golden-Plover). Individual variation often associated with molting during the non-breeding season will make some individuals (including extralimital records) difficult if not impossible to identify with certainty (10, 11, 12, 13, 14, 9).
Most males in definitive alternate plumage are easily separable to species: white neck stripe of American Golden-Plover terminates abruptly at upper breast, and flanks and undertail coverts black; in Pacific Golden-Plover, white continues past the breast forming an irregular but conspicuous wash along sides and flanks, and undertail coverts are predominantly white. The extent of lateral whiteness varies among male Pacific Golden-Plovers, with some individuals being more boldly patterned than others.
Females in definitive alternate plumage are less colorful, with variable numbers of whitish feathers on breast and face producing mottled appearance. Obvious sexual dimorphism is typical in Pacific Golden-Plover and in most American Golden-Plovers; some American Golden-Plover females are less mottled, darker (brownish black), nearly male-like in appearance. Basic and juvenile plumages are generally distinctive: head, neck, breast, and upperparts bright yellowish-buff in Pacific Golden-Plover, grayish in American Golden-Plover. However, subtle variation in juvenile and non-breeding plumage coloration sometimes renders this feature misleading (15, 11, 16, 12, 13, 17).
Body masses are similar in both species but extremely variable (about 100–200+ g) over the annual cycle. Abnormally low body mass can occur in some Pacific Golden-Plovers (usually juveniles) encountering stressful conditions during fall migration; emaciated individuals at or near death may drop to 50–70 g (18, 19). Similar weight loss is likely in American Golden-Plovers; an 86 g juvenile was reported in the Caribbean (20).
The Pacific Golden-Plover is smaller than the European Golden-Plover. Also, European Golden-Plover has mostly white wing-linings, whereas the underwing of Pacific Golden-Plover is smoky gray. Black axillars, white wing-stripe, and white rump and uppertail distinguish the Black-bellied Plover (Pluvialis squatarola) in all plumages from the three golden-plover species. Compared to the latter, alternate plumage of the Black-bellied Plover is particularly distinctive with silver-gray upperparts, white undertail, and more extensive white on the head, neck, and shoulders.
Most of this section is based on detailed descriptions of plumage, often for both Pacific and American golden-plovers combined (21, 22, 23, 24, 25, 26, 27, 28, 20, 29, 30, 10, 11, 31, 16, 12, 13, 32, 33; OWJ, unpublished data). Several of these sources (11, 16, 32) contain particularly helpful photographs of Pacific Golden-Plover (both sexes), in the plumages described below, often in comparison with American Golden-Plover. Additional published photos are available (e.g., 34, 9, 35, 36). Treatment by Byrkjedal and Thompson (37) complements our descriptions below, and includes useful diagrams and sketches. See Pyle (33) for detailed information on molt and age determination, and Dwight (38) and Stone (39) for early accounts of molts (primarily based on American Golden-Plover).
Pacific Golden-Plovers have 10 full-length primaries (numbered distally, p1 to p10), 15–16 secondaries (numbered proximally, s1 to s11, and including 4–5 tertials, numbered distally, t1 to t5), and 12 rectrices (numbered distally, r1 to r6, on each side of the tail); plovers are diastataxic (40), indicating that a secondary has been lost evolutionarily between what we now term s4 and s5. Wings are long and pointed and tail is short and squared. Geographic variation in appearance is slight at best (see Systematics: Geographic Variation). Geographic variation in wing-molt strategies has been reported (41), with birds breeding in western Siberia commencing primary molt before fall departure from nesting grounds, while birds breeding in Alaska mostly defer molt until after fall arrival on overwintering grounds.
Present June–July. Natal down well developed at hatching. Crown and back overall yellowish, mottled with fine black markings; except for crown and black malar stripe, remainder of head, throat, and nape solid whitish; underparts grayish white. Yellowish especially noticeable around head, nape, and throat (42, 43, OWJ). Whether sexes dimorphic uncertain.
Present primarily July–October. Similar to Definitive Basic Plumage but feathering more even in pattern and wear. Crown, mantle, back, scapulars, and tertials dark grayish brown, the feathers marked with brightish yellow edges and spots; rectrices grayish brown faintly barred dark brown, with small lateral yellow spots and fringed tips; lores moderately dark forming indistinct loral smudge; dark auriculars produce conspicuous postorbital patch; indistinct supercilia mottled whitish; upperwing lesser and median coverts same background color as upperparts with whitish, buffy, and yellowish markings; chin whitish; chest pale brown, mottled and spotted with darker brown; breast, sides, and flanks brownish white with grayish-brown barring, heaviest on breast and becoming finer and less dense on flanks; belly and undertail whitish. Sexes similar except for average differences in outer rectrices (see Formative Plumage).
"First Basic" and/or "Basic I" plumage of Humphrey and Parkes (44) and some previous authors. Present primarily November–March. Similar to Definitive Basic Plumage except for aspects related to retention of juvenile feathers in upperwing and tail. Distinctive breast to flank barring of Juvenile Plumage lost by early winter, after which body plumage closely resembles Definitive Basic. Juvenile primaries not molted (29, 45, 46, 33) and thus become progressively worn; most juvenile distal greater coverts and some tertials and (usually) outer rectrices also retained, contrasting with replaced formative scapulars, lesser, median, and proximal greater coverts, and (usually) 1–5 tertials . Outer rectrices (r6) helpful as age criterion if retained (most birds) since juvenile feathers are drab and unbarred (29; Figure 385 in 33). Sexes similar, except that dark barring on outer rectrices averages slightly more distinct in males than in females (Figure 385 in 33); this allows sex determination of some but not all individuals when used alone.
First Alternate Plumage
Present primarily April–September, although may not be present in all individuals (see First Prealternate Molt). Banding studies on breeding grounds (OWJ) and examination of migrants (Johnson 1985a) indicate that First Alternate Plumage is variable due to partial or limited molts. In both males and females, plumage aspect can appear nearly as developed as Definitive Alternate Plumage, through usually with varying degrees of partial alternate feathering, to resembling retained Formative Plumage with a few feathers replaced, which may or may not show color patterns of alternate feathers. The latter appearance is more common on individuals that remain on winter grounds for their first summer. Upperwing coverts and tertials often confusing as age criteria since variable number of Juvenile, Formative, and/or First Alternate feathers retained by some birds, replaced by others; however, worn juvenile outer primaries and some worn juvenile proximal upperwing greater coverts are retained in most or all birds, and these can be used to distinguish First Alternate from Definitive Alternate plumages, including for birds returning for their second winter in August–September and before the Second Prebasic Molt. Differences in body plumage generally cannot be used for sexing, except perhaps for a few males with well-developed First Alternate plumage appearance.
Definitive Basic Plumage
Present primarily October–March. See Definitive Prebasic Molt for information on appearance of breeding birds transitioning into Supplemental or Basic plumage before southbound migration. Upperparts including crown dark grayish brown with bright yellow, buffy, and whitish spots and fringes; rectrices barred light and dark grayish brown; sides of head grayish with darker auriculars and loral smudge and indistinct whitish supercilia. Upperwing lesser and median coverts gray-brown with pale yellowish margins and whitish tips; tertials gray-brown with indistinct pale yellowish margins and dusky bars; greater coverts, primary coverts, and remainder of remiges grayish, the greater coverts with indistinct white and dark bars along edges, the greater and primary coverts with white tips, and the primary shafts dark basally and terminally but white subterminally (especially conspicuous on outer 5–6 primaries). Underparts mostly brown with variable wash of pale yellow; belly and undertail whitish. During Prebasic Molt, plumage of males and females progressively less dimorphic as alternate feathering replaced. Following molt, sexes similar, except that outer rectrices (r6) about 80% sexually dimorphic with crisply defined dark gray/grayish white or black/white bars indicating male, and less defined (more somber) coloration indicating female (Figure 385 in 33).
In both sexes, Definitive Basic Plumage separated from Formative Plumage by basic primaries darker, fresher, and broader at tips, not becoming as progressively worn as juvenile primaries of Formative Plumage; upperwing coverts uniform in wear and quality and uniform with scapulars; tertials uniform in wear within tract and with other secondaries; outer rectrices (r6) more distinctly barred (29; Figure 385 in 33).
Second and Definitive Alternate Plumages
Present primarily April–September.
Male. Crown, nape, mantle, scapulars, tertials, and wing coverts dark grayish brown with bold, brightish yellow spots and fringes; sides of head and breast with continuous white stripe from forehead through supercilia, down sides of neck to flanks, widening slightly along sides of breast; sides of head (below white stripe); underparts primarily black, the vent often showing white feathers and the undertail coverts predominantly white (small percentage mostly to entirely black) (16, OWJ). Wings and tail as in Definitive Basic Plumage. Second Alternate Plumage is similar to Definitive Alternate plumage in most males, but a few birds possibly require an additional cycle, showing mottled whitish feathers, similar to but fewer than found in First Alternate Plumage (above); alternate plumages of some individuals may become progressively more extensive in successive cycles, with up to 3 yr before Definitive Alternate Plumage is acquired (needs further study).
Female. Similar to Definitive Alternate male but black feathering of face and underparts mottled whitish, grading into white head-neck stripe, resulting in the latter being less clearly defined than in male; auriculars often with distinctive white cheek patches. Male-like coloration rare in Pacific Golden-Plover females (contra 12, who reported “substantial overlap between sexes”), and darker individuals generally show white feathering on auriculars (OWJ). One instance of “male-like plumage” was reported among female Pacific Golden-Plovers on St. Lawrence Island (47). Although Nelson (48) described these plovers as sexually dimorphic in Definitive Alternate Plumage, the notion that sexes were alike persisted in early and later accounts (e.g., 21, 49, 50). Differences between male and female Definitive Alternate Plumages were set forth by A. C. Meinertzhagen (see 51) and confirmed in subsequent field studies (47).
Molt and plumage terminology follows Humphrey and Parkes (44), as modified by Howell et al. (52, 53). Pacific Golden-Plover exhibits a Complex Alternate Strategy (cf. 52), including a complete prebasic molt, a partial to incomplete preformative molt, and a limited to partial prealternate molt in both first and definitive cycles (Figure 2). A Definitive Presupplemental Molt of flank feathers has been reported in Pluvialis (54, 37, 55) but confirmation is needed (see 33 and below). Definitive appearance attained at the Second Basic and Second Alternate plumages, although possibly not until the Third Alternate Plumage in some males (see Alternate Plumages, above).
Prejuvenile (First Prebasic) Molt
Complete, late June–July, as young mature and forage on the tundra. One “nearly six-day-old male” American Golden-Plover had no juvenile feathers except for “barely visible” wing quills (56). Primaries also erupt at approximately 6 d of age. Prejuvenile Molt progresses rapidly, prior to fledging at < 30 d (see Breeding: Young Birds). Otherwise, no detailed information on timing or sequence of pennaceous feather irruption and development.
"First Prebasic" and/or "Prebasic I" molt of Humphrey and Parkes (44) and some previous authors. Molt occurs primarily or entirely on the overwintering grounds. Molting appears to start after arrival in Hawaii; duration about 2.5 mo, from October to early December (Figure 2). Juveniles traveling very long distances (into South Pacific) perhaps in molt before arrival on wintering grounds. Preformative molts differ in extent between Pacific Golden-Plover and American Golden-Plover (29, 30, 33): in Pacific Golden-Plover, it is partial to incomplete, occurring in September–December/March, and including most to all body feathers, some to most secondary coverts, often 1–5 tertials, and some rectrices, but usually no primaries, outer secondaries, or primary coverts (33). Rectrix molt variable and disorderly—some birds replace all rectrices, others very few, juvenile outer rectrix (r6) often retained. Most individuals show Preformative Molt patterns typical of shorebirds wintering in the Northern Hemisphere, although Individuals wintering farther south probably have more-extensive Preformative Molts, which may include outer primaries in an eccentric pattern in occasional individuals, as in other shorebirds that migrate to Southern Hemisphere (33).
First Prealternate Molt
Limited to partial, primarily March–May (Figure 2). Some of this molt can occur while en route north; e.g., Pacific Golden-Plovers overwintering in Australia depart in partial alternate plumage then molt during migration (45). In Hawaii, birds usually complete molt before departure. Extent of First Prealternate Molt can occasionally approach that of Definitive Prealternate Molt whereas in most individuals, particularly those that remain on overwintering grounds for first summer, molt can be limited to just a few body feathers or perhaps rarely can be absent. On Oahu, Hawaii (29, OWJ), First Prealternate Molt occurs from end of February to early May, with individual duration varying considerably within this period; replacement of body feathers and wing coverts variable, ranging from almost complete (body feathers) to about half (wing coverts), to none in either area; oversummering birds average less molt. From 1–4 tertials and/or 1–2 central rectrices occasionally replaced, but averages fewer feathers than in Definitive Prealternate Molt.
Second and Definitive Prebasic Molts
Complete, primarily July–November but extending to early March in some individuals that overwinter farther south (e.g., Australia; 45, 12; Figure 2). Second Prebasic Molt averages earlier in timing, especially for over-summering 1-yr-old birds. 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 occurring.
For breeding birds, Definitive Prebasic Molt can commence on breeding grounds during incubation (Figure 2). Early stages of molt most noticeable on black cheeks and underparts which become mottled with lighter feathers. Up to four inner primaries can occasionally also be replaced before southbound migration, most likely in failed breeders (57, 33). On Siberian breeding grounds, more than half of Pacific Golden-Plovers have begun Definitive Prebasic Molt by end of July (58), body molt begins early in incubation, and adults often molt inner primaries by mid July (59, 37, 60, 61; P. Tomkovich, personal communication). These observations consistent with condition of Pacific Golden-Plovers arriving on overwintering range: many birds wearing only traces of Alternate body feathering, often with suspended primary and rectrix molt. Individual duration of body molt approximately 2.5–3.5 mo (variable from late June through mid October); primary molt more protracted, requiring 4–5 mo (completed in most birds by early December); oversummering birds begin primary molt in June or July, several weeks earlier than migrants. Among Pacific Golden-Plovers wintering in Australia, average duration of primary molt also about 4 mo, but timing later (October–March) than in Hawaii (45).
Describing less colorful male Pacific Golden-Plovers in Prebasic Molt on breeding grounds, Sauer (47) mistakenly used term “eclipse.” Presupplemental Molt resulting in supplemental feathering with possible cryptic function has been described on underparts of breeding European Golden-Plovers in both sexes (54, 37). Whether ventral body molt of nesting Pacific Golden-Plovers involves like elements or simply represents late Prealternate Molt or early Prebasic Molt is unclear (55, 33).
Definitive Prealternate Molt
Partial, January–May (Figure 2), primarily on winter grounds but can complete at stopover sites or on summer grounds in some individuals; Second and Definitive prealternate molts similar in timing and extent. Includes some to most body feathers, up to 40% of secondary coverts, often 1–4 tertials, occasionally 1–2 central rectrices (which can be asymmetrical with 1 rectrix of a pair fresh and the other old); males average greater number of feathers replaced; e.g., in females typically only as much as 15% of wing coverts replaced (33). First birds to begin and complete Prealternate Molt usually males, with some males achieving full Alternate Plumage in about 10 wk.
Black in all ages, including hatchlings.
Dark brown throughout life.
Legs and Feet
Dark grayish brown to gray in hatchlings. In older birds, vary from gray and grayish black to black. Gray and grayish black seem to occur most often in juveniles (OWJ).
Earlier studies of linear measurements reported no significant differences between the sexes (66, 15, 20, 18, 12). A more recent study (9) found statistically significant differences in head, tarsus, and bill lengths, with females averaging smaller than males; however, differences were all < 1.0 mm and too small to be of practical application. With respect to age, there was no difference between wing lengths of adults and juveniles during fall (18). However, this relationship changes during the ensuing months as gradual wear of retained juvenile primaries shortens the wing considerably (> 6 mm lost by time of Second Prebasic Molt; see 45). In spring, when young birds are about 10 mo old, the difference in wing length between young and adult age groups was highly significant (9). Thus, age structure of the sample is an important, but often unknown or unreported variable in analyses of wing length.
Based on museum specimens, Pacific Golden-Plover wing lengths appear to vary on nesting grounds along a latitudinal cline, being shortest in western Siberia and longest in western Alaska (see 37, 41). This variation, along with differences in timing of wing molt, led Jukema et al. (41) to propose that the Alaskan and Siberian populations represent separate subspecies. Contrarily, there was little variation in wing length of living birds (a few freshly collected) at several sites from the Taimyr Peninsula (Far North Russia) to western Alaska (9), all measured with the same technique (flattened and straightened primaries). By contrast, the wing length differential between two large samples from widely separated migratory corridors (Oahu on Mid-Pacific Flyway versus Torey Depression, Mongolia, on the transcontinental Asian Flyway (Appendix 1) is highly significant (P = 0.0001). These results (Oahu sample significantly longer-winged than Torey Depression sample) tend to support the foregoing cline and possible subspeciation as there is strong migratory connectivity between Oahu and Alaska, whereas plovers stopping over in the Torey Depression are likely en route to Siberian breeding grounds.
Upon arrival at the breeding grounds, most birds are probably carrying fat reserves, but no precise measurements are available. Limited and sometimes conflicting information on mass change during subsequent weeks may reflect regional variation in food supplies and weather. In a small sample of Pacific Golden-Plovers from Chukotka, Far East Russia, males (n = 5) averaged about 30 g less than post-laying females (n = 2), suggesting that reproductive duties were more stressful on males (58). Mass measurements for nesting plovers on the Seward Peninsula, Alaska, and the Taimyr Peninsula, Far North Russia, suggest a similar possibility. (Appendix 1).