Food Habits

Feeding

Main Foods Taken

Invertebrates, primarily terrestrial, some freshwater and marine; also berries, leaves, seeds. Studies in other shorebirds (Proctor 1968) suggest these plovers might retain seeds in digestive tract, transporting them over great distances during migrations. Small vertebrates known to be eaten occasionally by Pacific Golden-Plover; probably also by American Golden-Plover, but definite evidence lacking. On breeding grounds near Churchill, American Golden-Plover tends to forage selectively on relatively large prey (Baker 1977).

Microhabitat For Foraging

Varies with annual cycle and geographic location. Generally prefer microhabitats where plant cover is short or absent, allowing ease of movement and relatively unobstructed vision. Breeding birds forage on various types of tundra ranging from large expanses of low vegetation only a few centimeters tall (as on well-drained slopes) to wetter mosaics of low shrubs and grasses interspersed with openings. When young hatch, families move to moist shrub/grass areas for feeding and cover. Migrants and wintering birds feed on wide array of substrates (see Habitat, above). Clear preference for soybean stubble by American Golden-Plover in w. Indiana, possibly because less insecticide is used on this crop, resulting in greater abundance of soil insects (Erickson 1992); also soybean fields less tilled than other crops and this may favor larger populations of earthworms (Braile 1999). Both species attracted to rice fields on winter range and during migrations (Watanabe 1991, 2001; Maeda 2001; Blanco et al. 2006a; Chan et al. 2007). In open stands of ironwood (see Habitat: winter range, above), trees shed coniferlike leaves, forming a dense insect-rich mat on which Pacific Golden-Plovers forage. Where adapted to urban conditions of Hawaii, Pacific Golden-Plovers often glean insects from paved surfaces adjacent to grass and other low vegetation.

Food Capture And Consumption

Forage by repeated sequence of stop-run-stop or “run-stop-peck” (Byrkjedal and Thompson 1998). At stop, either prey captured (usually after brief scanning of substrate), capture attempt fails, or no prey seen. Capture is with single peck or series of pecks. Probing while feeding on earthworms reported in American Golden-Plover (Wishart et al. 1981); possible tactile feeding by shallow poking in mud (probably both species) noted by Paulson (1993). When feeding on lawns in Hawaii, Pacific Golden-Plovers often peck vigorously and dig shallow holes, beak and portion of head sometimes buried in the turf; smaller prey and earthworms generally swallowed whole, large roaches and millipedes usually broken up by pecking and swallowed piece by piece (OWJ).

Sometimes run for several meters and immediately seize prey, indicating excellent visual perception. Probably most food recognition and choice related to eyesight; except for brief comments about probing above, no information concerning senses of taste, smell, touch. Berry-eating on tundra does not involve usual foraging behavior just described; instead bird pecks repeatedly in small area. Birds foraging amidst low bushes on breeding grounds sometimes peck leaves at eye level or above, likely capturing tiny spiders or insects (probably mosquitoes which were abundant when behavior was observed; OWJ). Spatial separation maintained during feeding; no cooperative foraging. Foraging behavior varies with reproductive duties (see Breeding: incubation, below): if incubation underway, birds forage alone during off-duty hours; if not yet incubating or if eggs have hatched and parents are guarding young, mated birds usually forage together.

Wintering birds feed alone on territories well separated from neighbors, or in more closely spaced groups often consisting of nonterritorial individuals (see Behavior: spacing and agonistic behavior, below). General pattern is to return to feeding grounds before sunrise, forage during daylight hours, then gather at communal roosts for the night (see Behavior: self-maintenance; also Demography and Populations: range, below). Pacific Golden-Plovers observed feeding at night on Johnston I. (OWJ) and in northern New South Wales (Rohweder and Baverstock 1996), the extent of this behavior elsewhere is unclear in both species.

Diet

Major Food Items

Many foods common to both species (Bent 1929, Byrkjedal and Thompson 1998): various adult and larval insects such as grasshoppers, beetles, grubs, cutworms, wireworms; earthworms; small molluscs and crustaceans; spiders; crowberries (Empetrum) and blueberries (Vaccinium). Regional reports list numerous foods including: for American Golden-Plover—seeds of Sylibum marianum (Argentina; Dabbene 1920); berries of Arctostaphylos uva-ursi, spiders Lycosa sp., weevil Otiorhynchus ovatus, ichneumon wasp, beetle larvae (Nantucket; Mackay 1892, 1929); fiddler crabs Uca uruguayensis (Argentina; Iribarne and Martinez 1999); beetles, ants, flies, grasshoppers, crickets, spiders, isopods, snails, earthworms, seeds, plant parts (Argentina; Isacch et al. 2005); weevils, ants (Illinois; Brooks 1967); earthworms (s. Manitoba; Wishart et al. 1981); for Pacific Golden-Plover—crane fly larvae, beetles, spiders, slugs, earthworms, freshwater crustaceans, crowberries (Siberia; Dementiev et al. 1951, Kondratiev 1982, Khlebosolov 1983, Kistchinski et al. 1983, Dorogoy 1988); assorted annelids, molluscs, crustaceans, leaves, and seeds, many kinds of insects, small fish, lizards, even birds’ eggs (Africa, Australia, Laysan I.; Urban et al. 1986, Lane 1987, Marchant and Higgins 1993, Olson 1996); brine shrimp (Laysan I.; M. Naughton in litt.); skinks (Canton I., Gilbert and Ellice Is.; Child 1960, Palmer 1967); grubs of emerald beetle Protaetia pryeri (Midway Atoll; Nishida and Beardsley 2002); polychaetes and mussels (Malay Peninsula; Kato et al. 2000); leafhoppers (Nephotettix cincticeps), earthworms, leeches (rice fields, Japan; Watanabe 2006, 2007); noctuid moths and caterpillars (Hawaii; Perkins 1903); roaches, bees, ants, dipteran flies, earwigs, earthworms, sowbugs, mites (Hawaii; Okimoto 1975); slugs, millipedes (Hawaii; OWJ); blind snake, skinks, geckos, flowers and leaf parts from Bidens sp., Indigofera spicata, and other unidentified plants (Hawaii; P. Bruner and A. Bruner pers. comm.); possibly small mice (Hawaii [OWJ], Johnston Atoll [D. O’Daniel in litt.]).

Berries particularly important in spring and fall. At spring arrival, over-wintering berries from previous year may be one of few foods available. The latter sometimes very abundant, McCaffery (1996) noted that densities may reach 200,000/ha. New berry crop used by fall migrants during stopovers (reported in American Golden-Plover by Mackay 1891; also see Todd 1963) and no doubt by juveniles remaining on breeding grounds after departure of adults (see Migration: timing and routes of migration, above). Fallout of airborne arthropods on snow patches might provide limited early spring food source (Edwards and Banko 1976).

An injured Pacific Golden-Plover adapted readily to feeding in captivity (on earthworms, insects, snails, tail of salamander) and was conditioned to take food from the hand within 6 d (Williams 1952). Various human/plover feeding relationships occur in Hawaii where some wintering Pacific Golden-Plovers learn to glean discarded scraps of food (bread, rice, chicken, french fries, apple) on lawns or pavement (P. Bruner and A. Bruner pers. comm., OWJ); one individual learned to take earthworms from the hand (A. Dibben-Young in litt.), another became conditioned to alight on the palm of an outstretched hand from which it ate mealworms (B. Riddle in litt., plus photos given to OWJ); and plovers offered french fries in parking lot of a fast food restaurant learned to carry them off (held in their beaks) to nearby rooftops so as to avoid competition from Common Mynas (Acridotheres tristis) and other birds (OWJ). Natural foods are very limited on tiny Johnston Island, central Pacific Ocean, and plovers wintering there learned to gather in flocks (up to 150+) at certain times of day for supplemental feeding (mostly scraps of bread) by island residents (Johnson et al. 2004c). Such behavior raises possibility that artificial feeding might be a useful management tool for this species in some situations.

Thousands of carcasses from commercial seal harvest in Pribilof I., AK, formerly produced myriad of insects used by migrating shorebirds (see Thompson 1973), including Pacific Golden-Plovers. This localized trophic resource much diminished in recent years since killing of seals is now restricted to subsistence hunting only.

Quantitative Analysis

American Golden-Plover. On Nantucket Is., MA, “many” stomachs from birds shot in fall filled with little else than crickets (Mackay 1891); at Churchill, MB, 13 specimens had eaten approximately 41% plant seeds, 20% unidentified snails, 17% Chironomidae larvae, 9% Tipulidae larvae, 5% Dolichopodidae larvae, 5% Chrysomelidae Donacia adults, 1% Diptera eggs, 1% Dysticidae Agabus larvae, 1% unidentified adult Coleoptera (Baker 1977).

Pacific Golden-Plover. On Pribilof I., AK, 2 stomachs contained 72.5% beetles (mostly Pterostichus sp., Amara sp., and Carabus truncaticollis; also Chrysomela subsulcata and Staphylinidae), 22.5% flies (primarily larval Tipulidae), 4.0% Hymenoptera (partly wasp Amblyteles alpestriformis, plus unidentified species), 1.0% crowberry (Empetrum nigrum) seeds (Preble and McAtee 1923); on Wrangel I., Russia, 3 birds had collectively eaten 65 Tipulidae larvae, 11 Diptera larvae, 3 ground beetles, 1 leaf beetle, and 3 small lemming bones (Dorogoy 1982); on Yamal Peninsula, Russia, 1 individual collected 19 Jun contained 26 gnats (Empidae), 1 mosquito, and 2 beetles, another taken 31 Jul contained 2 beetles plus beetle larvae (Danilov et al. 1984); in Kolyma River region of Russia, 15 birds (10 adults, 5 chicks) were feeding extensively on oligochaetes, rapid dissolution of which in stomach may obscure relative importance of this food in overall diet (Khlebosolov 1983); 4 analyses from Oahu, HI: (1) 4 birds feeding on grassy area contained 91% insects (primarily weevil Sphenophorus venatus vestita), 9% miscellaneous (grit, unidentified plant material, feathers), (2) 16 birds from saline mudflat had eaten 69% insects (mostly S. v. vestita), 17.5% crustaceans, 13.5% same miscellaneous as in (1), (3) 3 specimens collected on another saline mudflat contained 47% crustaceans, 17% melanid snails, 1% Coleoptera, 35% same miscellaneous as in (1), (4) 33 birds from grazed pasture contained 86% insects (Coleoptera, Isopoda, Orthoptera), 14% same miscellaneous as in (1), plus lead shot and snails (Morita and Walker 1964, Saito and Walker 1972).

Nutrition And Energetics

No specific information. As noted above, lemming bones (presumably scavenged from pellets and scats of predators) occasionally found in plover stomachs, hence this material may be a calcium source for eggshell production and growth of juveniles (see Underhill 1994). Stomach samples from Eurasian Golden-Plovers suggest that females ingest bones, males do not (Byrkjedal and Thompson 1998), no comparable data for American and Pacific Golden-Plovers. Since small bones are not predictably available, and since stomachs from shorebirds collected on tundra breeding grounds often contain no calcareous material (Piersma et al. 1996, Jehl 2004), it remains uncertain how females acquire sufficient calcium for egg-laying which sometimes includes a replacement clutch (see Demography and Populations: measures of breeding activity, below). There is no information on body mass of these plovers at arrival on nesting grounds, and the energy demands associated with egg-laying, incubation, etc, have not been explored. Based on studies of other shorebirds, energy stores at arrival on breeding grounds (capital) may be partly used for egg production, but the latter is likely to depend mostly on nutrients acquired after arrival (income) [Klaassen et al. 2001, Morrison and Hobson 2004, Tulp 2007].

Metabolism And Temperature Regulation

Studies of wintering adult Pacific Golden-Plover by Mathiu et al. (1989) showed: basal metabolic rate high and passerine-like at 1.31W ± 0.41 SD, n = 12; mean rectal temperature 40.5°C ± 0.6 SD, n = 11; and average rate of weight loss during captivity 0.61g/h ± 0.13 SD, n = 9; BMR possibly higher on nesting grounds (see Lindström and Klaassen 2003). No comparable measurements for adult American Golden-Plover. As for young of the 2 species, metabolic rates, temperature regulation, time budgets, and body temperatures in relation to ambient temperatures have been studied only in the American Golden-Plover (Visser and Ricklefs 1993, Krijgsveld et al. 2003, Williams et al. 2007; see Breeding: parental care below). Visser and Ricklefs (1993) measured resting and peak metabolic rates (RMR and PMR) in one neonate at 0.126W and 0.200W, respectively. Williams et al. (2007) tracked these rates (in kJ/day) as follows: from neonates to immature birds weighing about 80 g approximate RMR increases from 10 to 100 (n = 19), and approximate PMR increases from 25 to 300 (n = 17). Energy requirements considerably in excess of predicted levels have been demonstrated in chicks of arctic-breeding shorebirds including American Golden-Plover (see Schekkerman et al. 2003), such requirements are associated with cold tolerance, rapid growth rates, and reproduction timed to arthropod abundance.

Drinking, Pellet-Casting, And Defecation

Requirements for drinking in these species unknown. Large flocks of American Golden-Plovers gathered daily noon to mid-afternoon for drinking and bathing at freshwater wetlands on Argentine winter range (Hudson 1920, Myers and Myers 1979). Similar flights of Pacific Golden-Plovers to watering places observed years ago in Hawaiian I., but no recent reports (Henshaw 1902, Perkins 1903, Schwartz and Schwartz 1949). On Oahu wintering grounds: Pacific Golden-Plovers often drink and bathe in puddles after or during rain (Johnson et al. 1981); availability of puddles highly variable, sometimes extended periods without precipitation; hot, dry conditions prompt frequent head-shaking to toss droplets of moisture from beak, suggesting nasal salt glands (supraorbital glands) important for water conservation (OWJ). Skull morphology indicates Pacific Golden-Plover has larger supraorbital glands than American Golden-Plover, difference suggests the former better adapted to marine environments during the non-breeding season (Byrkjedal and Thompson 1998).

No reports of pellet-casting, but occasional regurgitation of pellets or unconsolidated particles may occur, based on observations in other shorebirds. Nothing unusual concerning defecation.