Food Habits

Main Foods Taken

Broad diet. Main foods are marine invertebrates, including brachyuran crabs and other crustaceans, marine worms, and mollusks; also fish. On breeding grounds, takes insects, berries, sometimes flowers.

Microhabitat For Foraging

On arrival at breeding grounds, forages in ericaceous heath habitats. At Churchill, Manitoba (MB), feeding habitats characterized by lichens, mosses, crowberry (Empetrum nigrum), blueberries (Vaccinium spp.), and alpine bearberry (Arctostaphylos alpina). Also feeds on intertidal prey if available. Moves to sedge tundra and heath tundra when these thaw; these areas characterized by willows, andromeda (Andromeda polifolia), dwarf birch (Betula glandulosa), Dryas integrifolia, lapland rosebay (Rhododendron lapponicum), grasses, and lichens; in low, wet areas, also by mosses and aquatic sedges (Murie 1963, Mallory 1981).

During migration feeds on marine invertebrates in varied coastal habitats: mud flats, sandy beaches, rocky beaches, and salt marshes. In fall, also feeds on new berry crop in upland ericaceous heaths in arctic and subarctic areas; in heath-shrub habitats on Cape Cod, MA (Mackay 1892, Montevecchi and Tuck 1987). Other upland habitats used include dunes, wet meadows, pastures, and fields.

On winter range, forages along coast near mangroves or on tidal mudflats, sandy or rocky beaches, or estuaries; sometimes on nearby grasslands, lawns, and golf courses for insects (Herklots 1961, Mallory 1981), particularly in rainy season (EPM).

Food Capture And Consumption

From Mallory 1981, except where noted. Long and decurved bill appears to be adapted to feeding on intertidal prey (Fig. 2). In successful captures in Panama (n = 1,895), bill is inserted in substrate at all ranges of its length: 23% of the time, only tip is inserted; 15%, ≤ one-quarter of bill length; 16%, one-quarter to one-half of bill length; and 46%, ≥ one-half of bill length. Usually only bill tip is used to feed on insects (99.4% of captures at Churchill, MB; n = 362) and berries (70.5% picked with use of bill tip vs. 29.5% with one-quarter of bill length inserted into bushes; n = 61). Bill decurvature matches curve in fiddler crab (Uca spp.) burrows in Panama, and to a lesser degree on Cape Cod, MA. In water, bill is oriented perpendicular to surface, presumably to avoid refractive distortions (Velásquez and Navarro 1993).

Essentially a visual forager. In terrestrial habitats, feeds throughout daylight hours: at Churchill, MB, forages 44.3% of the time (another 11.5% spent walking, which may include search time); in Cape Breton I., Nova Scotia (NS), 82.3% of the time (another 2% spent walking). In coastal habitats, feeds in intertidal when flats are exposed; also at night if energy requirements are not met during day. At high tide may shift to nearby terrestrial areas; may roost (even in trees) until next low tide. On Cape Cod, MA, birds for-aged 55.2% of the time observed (spent another 4% walking); in Panama, they foraged 90.3% of the daytime and some more at night. In Venezuela, they feed primarily during day in upper intertidal zone during high and low tides (Robert et al. 1989).

In Mauritania in Feb, Whimbrels feed during 79.5% of daytime low water period but not at night, but in Apr they increase to 84.3% of daytime low water period with some nocturnal feeding; results in about 33% more feeding time in Apr (when putting on premigratory fat) relative to Feb (Zwarts et al. 1990a). In South Africa, birds feed on mudprawns (Upogebia africana) during day (60% of intake) and night low tides; at night feed more slowly and in smaller areas, and sight prey at shorter distances, but maintain similar peck rate: fewer, but larger, prawns captured (0.31/min vs. 0.56/min by day), resulting in similar energy intake rates (1.24 kJ/min vs. 1.53 kJ/min by day; Turpie and Hockey 1993).

Birds foraging on polychaetes in Chile have step length of 12.5 ± 0.3 (SE) cm (n = 238) and walking speed in wet sand of 12.2 ± 0.4 m/min (slower in water, water film, or muddy areas). Lowest probe rate (32.2 ± 1.0/min) but highest success (73.9 ± 1.9%) occur in wet sand; ingestion rate similar in wet sand, water film, and standing-water sandy areas, but lower in muddy areas (Velásquez and Navarro 1993). Birds are spaced more evenly and are more aggressive in sandy than in muddy areas.

When feeding on berries, bird walks, stopping to pull 1 or several berries off branch with tips of mandibles. Bird jerks its head back, opens bill to catch berry in its throat, and swallows it. Foraging on insects is similar, with <1% of captures requiring additional handling (n = 366). Often snatches insect while walking; in warmer temperatures, often lunges. Larger prey (beetles, bees, crabs, fish, mollusks, marine worms) are often first knocked on hard surface until subdued.

When foraging on intertidal prey, walks up to or lunges at prey; pecks with bill tip or probes. In soft mud, a puddle, stream, or open water, may submerge face to grasp prey; sometimes rapidly pumps bill up and down. Pulls a worm steadily until it is extracted or breaks. Usually probes once when foraging for crabs, often rotating bill to follow curved burrow; may wait at entrance for crab to appear. After extraction with bill tip, small prey are handled like insects and berries; a muddy crab is often rinsed first. Bird uses bill to break off claws and legs of a large crab, then swallows carapace; eats all but largest claws. A captive bird fed only crabs refused a greater portion of the skeleton as food was made more available (Zwarts and Blomert 1990). In Panama, crab capture appears limited not by crab numbers but by crabs’ defensive behavior of wedging into a burrow at any movement.

Major Food Items

Arriving on breeding grounds, subsists on previous summers’ berries, including crowberry, bog blueberry (Vaccinium uliginosum), mountain cranberry (V. vitis-idaea), and bearberry (Arctostaphylos spp.; Murie 1963, Mallory 1981). Switches to insects as these become abundant: primarily Diptera, but also Hymenoptera and Coleoptera. During cold rainy weather will eat flowers of ericaceous plants near nest (EPM). By late Jul, feeds on new berry crop. In Labrador and other Maritime Provinces, migrants feed on abundant berries of crowberry, blueberries, and cloudberry (Rubus chamaemorus); on Cape Cod, MA, on blueberries and huckleberries (Gaylussacia spp.); also forage on insects, including beetles (e.g., Lachnosterna [Scarabaeidae]), grasshoppers, and spiders (e.g., Lycosa) in upland heath dunes, wet meadows, and fields (Mackay 1892, Montevecchi and Tuck 1987).

For migrants and wintering birds, crabs are major prey from both coasts of U.S. south to central South America (Barruel 1968, Mallory 1981, Paulson 1993). Primary prey in intertidal habitats: Brachyura crabs, including Uca pugnax and U. pugilator on Cape Cod, MA, and a variety of Uca crabs (e.g., Uca heteropleura and U. panamensis), Spiocarcinus ostreacola, swimming crabs (Portunidae), and mud crabs (Xanthidae) in Panama; other crustaceans, e.g. Crangon septemspinosus on Cape Cod, Emerita rathbunae on sandy beaches in Panama; and marine worms, e.g., Sipunculida and sea cucumbers (Holothuroidea) in Panama (EPM). Also polychaetes (Perinereis gualpensis in Chile; Velásquez and Navarro 1993), bivalves, gastropods (e.g., marsh-dwelling Melampus coffeus in Suriname; Barruel 1968), fish (e.g., Gobiidae, Gobiosoma sp. in Panama; EPM), and marine insects. Sometimes striped shore crab (Pachygrapsus crassipes) on rocky shores in s. California (G. Lukner pers. comm.); crayfish (Cambarus bartoni) in rice fields of Louisiana and Texas (Harrington and Page 1991) and likely elsewhere in freshwater marshes; and insects (e.g., crickets and grasshoppers) on lawns (EPM).

Quantitative Analysis

From Mallory 1981 except where noted. At Churchill, MB, birds in terrestrial habitats consumed 64% insects, 11% berries, and 25% unidentified items. Ericaceous seeds predominated in 11 of 12 fecal samples at Cape Breton I., NS; insect parts were a major item in 3 samples and a minor item in 4; a snail shell piece was in 1. From late Jul to mid-Aug at Cape Cod, MA, in a marsh with abundant fiddler crabs, Whimbrels consumed 36% crabs, 0.6% fish, 0.6% shrimp, 0.6% worms, and 62% unidentified items. In Panama, 91% of identified prey were crabs, 6% fish, 1.6% mollusks, and 1.3% worms; of 15 fecal pellets from mudflats, crab parts were a major item in 12 pellets and a minor item in 2, clams were a major item in 3 and a minor item in 2, and worms occurred in 2. In Chile, 65 fecal pellets and 4 stomachs of birds feeding on an estuarine mudflat contained almost exclusively large intertidal polychaetes (Perinereis gualpensis; Velásquez and Navarro 1993).

No information.

Crabs are only 65% (55–76%) digestible versus 74% for other invertebrates and 78% for fish. Whimbrel metabolizes 99% of fat, 74% of pro-tein, and 1% of carbohydrates of crabs (Zwarts and Blomert 1990). Total energy content of crabs is 10.7 kJ/g dry mass (DM), but apparent (energy input minus energy output in feces and urine) and true (excluding urinary energy output) metabolizable energy content are 7 and 8 kJ/g DM, respectively. Caloric content of other estuarine prey is higher: 20–25 kJ/g DM. A bird can consume 2–3 mg ash-free DM of crabs/s; at high intake rate, however, a bird pauses for digestion, resulting in maximum intake of 1 mg/s (Zwarts and Dirksen 1990).

Maintenance metabolic rate for captive birds wintering in Mauritania is 289 kJ/d; a bird needs 43 g of fiddler crab DM (21 g if ash-free dry mass [AFDM]), or 450 kJ/d, to maintain its body mass (Klaassen et al. 1990, Zwarts and Dirksen 1990). Estimated basal metabolic rate (BMR) is 211 kJ at a mass of 369 g; after starving, BMR is 196 kJ at a mass of 333g (Zwarts and Dirksen 1990). Daily net energy intake during winter is 1.5 x BMR (2.1 x “tropical BMR”); in Apr increases to 2.1 x BMR (3.1 x “tropical BMR”). For a weight gain of 1 g, food intake must increase by 1.3 g DM (0.6 AFDM) of fiddler crabs, or 26 kJ.

Birds wintering in Mauritania drink sea water 0.9 (0–29) times/hour at low water; frequent drinking may be due to heat stress (Zwarts and Dirksen 1990). Maintenance metabolism lower in tropical Mauritania than in temperate areas; reduced endogenous heat production may reduce heat stress (Klaassen et al. 1990).

Not recorded drinking water in Americas (but see above). When feeding on intertidal prey, defecates every 16.5 min (11.4–37.4) in Panama, every 17.7 min on Cape Cod, MA, every 21.4 min in Cape Breton I., NS; when foraging on insects and berries, every 22.5–33.6 min at Churchill, MB (EPM). In Mauritania, defecates every 2–20 min when feeding; energy content of excreta varies from 5 to 20 kJ/g DM, 20–50% of original energy in food (Zwarts and Blomert 1990).