Food Habits

Main Foods Taken

Benthic invertebrates (small arthropods, molluscs, and annelids) in fresh or salt water, also some terrestrial invertebrates (insects and spiders).

Microhabitat For Foraging

In coastal areas, foraging is usually regulated by the tidal cycle, with most feeding as water recedes and at low tide on mud-silt substrates (Recher 1966, Burger et al. 1977, Boates and Smith 1989). In some intertidal areas (e.g., southern James Bay), marsh edges are also used extensively when invertebrate food is abundant (Morrison 1984). Elsewhere, this sandpiper forages along the edges of lakes, open alkali ponds, and sewage lagoons (Lewis 1983, Young 1989, CLG-T); in recently-dry or damp (often muddy) substrates and up to tarsus-deep water levels, usually in open areas without extensive vegetation (Brooks 1967, Baker 1973, Lank 1983). Foraging microhabitat can vary according to time of day, season, or location, and appears primarily related to food abundance and availability (e.g., Morrison 1984). No sexual differences in habitat selection have been described, although in Massachusetts birds that fed by probing in soft mud averaged longer bills than those probing in mud-sand substrates (Harrington 1982). Juvenile females in the Bay of Fundy consumed significantly larger amphipods than juvenile males, presumably because they could probe deeper (with their longer bills) into the burrows of larger prey (Gratto et al. 1984).

Food Capture And Consumption

Feed either by pecking or probing. Foraging method depends on type of invertebrates available: tactile probing for burrowers, or visual pecking for surface prey . Hunting is visual early in tidal cycle, as birds follow receding waterline, then tactile on mudflats at low tide (Harrington 1982). Primary prey in Bay of Fundy, amphipod Corophium volutator, is most readily available when it is crawling on the surface of the mudflat. Since amphipods crawl much less after sandpipers arrive during fall migration, most are obtained then by probing (Boates and Smith 1989). In Saint Lawrence River estuary, most birds foraged by probing at average of 85 probes/min (Michaud and Ferron 1986). On breeding and wintering grounds, they pecked faster than other Calidris sandpipers (Baker 1973). In sewage treatment ponds in the Northwest Territories, they fed visually on surface 97% of time, and probed seldom (Young 1989). In Alaska, they were also predominantly surface feeders along the edges of ponds (MacLean 1969). Multiple and single pecks were the most common foraging techniques at small ponds in prairie Canada during migration (Lewis 1983). In Peru, birds probed and pecked equally in water, probed one third and pecked two thirds of the time in wet mud, and pecked only on dry substrates (Ashmole 1970).

Although little studied, individuals do forage at night (e.g., Gratto et al. 1984, Robert et al. 1989).

During spring migration (late May–early June) in Saskatchewan, Anostraca, Conchostraca, Copepoda, Hydrophilidae, and Orthocladiinae larvae were commonly taken; chironomid larvae and curculionids were rare (Lewis 1983).

Diet during breeding season was examined in Manitoba (Baker 1977) and Alaska (Holmes and Pitelka 1968). In Manitoba, 60% of food items were chironomid larvae (Diptera), 20% unidentified arachnids, and < 10% plant seeds, tipulid larvae (Diptera), dolichopodid larvae (Diptera), uni-dentified snails, Donaciaadults (Chrysomelidae, Coleoptera), Lispelarvae (Muscidae, Diptera), Agabuslarvae (Dytiscidae, Coleoptera), Pericomalarvae (Psychodidae, Diptera), and Hyrgotusadults (Dytiscidae, Coleoptera). Most invertebrates taken were 2–5 mm long. In Alaska, 60% of food items in June were chironomid larvae (most 5–10 mm long), 15% tipulid larvae (primarily Pedicia, with many fewer Tipulaand Prioncera), 15% arachnid, and 10% staphylinid adults, coleopteran larvae, and carabids. One month later in Alaska, adult insects were taken much more often, with 50% small dipterans, 7% adult tipulids, 3% arachnids, and 40% 5–10 mm chironomid larvae (Holmes and Pitelka 1968).

During fall migration (July–September) in Saskatchewan, ephydrid, chironomid, and orthocladiine larvae were most frequent prey, followed by ostracod and hydrophilid adults and larvae, tanytarsine larvae, muscid larvae, and corixids (Lewis 1983). In Illinois, free-swimming hydrophilids and dytiscids, benthic hydrophilids and physids, and algae were taken (Brooks 1967). In southern James Bay, Ont., when feeding in marshes, all individuals ate dipteran larvae and 7% ate oligochaetes. When on mudflats, 80% ate the small bivalve Macoma balthica,and 80% the small gastropod Hydrobia minuta(Morrison 1984).

During fall migration in Saint Lawrence River estuary, Que., birds ate very abundant small polychaetes, Nereis virens(Michaud and Ferron, 1986). In all studies in Bay of Fundy, Corophium volutator(Amphipoda) were by far the most common prey (average length taken 4–6 mm). Other prey: foraminifera; gastropods Littorina littorea, L. obtusata, Hydrobia minuta, H. totteni, Ilyanasa obsoleta; pelecypods Nucula proxima, Gemmaspp.; polychaetes Streblospio benedicti, Nephtysspp., Nereis virens, Heteromastus filiformis; ostracods; copepods (Harpactecoida); amphipod Dulichia portecta; nematodes; and some dipteran insects, mostly chironomid larvae and pupae (Hicklin and Smith 1979, Boates 1980, Gratto et al. 1984, Peer et al. 1986).

During fall migration in coastal Massachusetts, the most common invertebrate taken was shrimp Crangon septemspinosa(> 50% by volume), 0.5–2.0 cm in length. Less common prey were haustoriid amphipods, Acanthohaustoriusmillsiand Trichophoxus epistomus(> 0.2 cm), and nonnereid polychaetes (> 2 cm). Small clams, Gemmaspp., were common but virtually all intact and undigested, so they may have been taken accidentally (Schneider and Harrington 1981).

On wintering grounds in Suriname, tanacids (Crustacea) were considered common prey (Spaans 1978).

Average caloric content of Corophium volutator< 4.5 mm was 15.1 J/mg dry weight, and > 4.5 mm was 17.2 J/mg dry weight (Boates and Smith 1979). Chironomid larvae produced 20.0 kJ/g dry weight, and other insect larvae (small diptera, tipulids, and coleopterans) 21.9–23.9 kJ/g dry weight. Adult insects ranged from 20.9 for arachnids to 23.9 for small dipterans (Custer inAshkenazie and Safriel 1979b). Mean dry weights of 5–10 mm chironomid larvae were 0.07 mg, > 10 mm chironomid larvae 0.66 mg, small adult diptera 0.15 mg, and arachnids 1.41 mg (Holmes in Ashkenazie and Safriel 1979b).

Fecal pellets not useful in determining diet, as few prey species can be later identified (Schneider and Harrington 1981).

Considered unusual in that these birds are small-bodied but selective in diet (Baker 1977). Foods taken vary among areas, but at each site and time birds usually concentrate on prey species most abundant and available; hence, selective but opportunistic. May select Corophium> 4 mm (Peer et al. 1986), but may underutilize those > 7 mm, perhaps because they cannot be reached in deeper burrows (Gratto et al. 1984). Predation shown to reduce abundance of invertebrate prey (Boates and Smith 1979, Schneider and Harrington 1981, Peer et al. 1986).