Food Habits

Main Foods Taken

Freshwater, marine, and terrestrial invertebrates. Occasionally plant material and rarely small fish.

Microhabitat For Foraging

Varies by habitat and season. On breeding grounds in w. and n. Alaska and Hudson Bay, Canada, feeds on rims and troughs of polygons, hummocks, wet marsh dominated by Carex, Eriophorum, and Dupontia, edges of interior lakes and ponds, and coastal ponds and lagoons (Holmes 1966a, J. Jehl pers. comm.). On wintering grounds, along estuaries dominated by mudflats; at Bolinas Lagoon, CA, most often on mudflats composed of well- to moderately sorted fine sand (Page et al. 1979); usually feeds at tide line (Brennan et al. 1985), in water 0–5 cm deep (NDW). In Europe, individuals feed selectively in small depressions and runnels on mudflat where they are able to penetrate the substrate easily (Mouritsen and Jensen 1992). During northward migration (Alaska), feeds at tide line on mudflats on both rising and falling tides; foraging discontinued on high tide and resumed within 1 h of high tide (Senner et al. 1989). In Europe, during migration, foraging habitat differs day versus night; lower densities of foraging birds on mudflats at night; higher densities on Corophium bed at night (Mouritsen 1994).

Food Capture And Consumption

Tactile feeder that probes, jabs, and picks in substrate, often with open bill (see Bent 1927: 220). Open bill may permit access to taste buds (Heezik et al. 1983); species may surface tension feed as do Western Sandpiper, Least Sandpiper (Calidris minutilla), and Red-necked Phalarope (Phalaropus lobatus) (M. Rubega pers. comm.). Taste and visual cues used to find prey (Heezik et al. 1983, Evans 1986). Rarely probes deeper than 3.5 mm (Mouritsen and Jensen 1992); rarely probes on breeding grounds in Alaska, instead jabs and pecks (Holmes 1966a). Most common form of foraging for C. a. hudsonia is multiple probing; foraging rates slower in summer than winter (Baker and Baker 1973). Foraging rate of migrating birds shown to be faster at night than in day (Mouritsen 1994).

For Europe see Cramp and Simmons 1983 .

C. a. pacifica

Staging. Prey base predominantly bivalves and amphipods. On Yukon-Kuskokwim Delta, AK (Jul–Oct), Macoma expansa found in 100% of stomachs (n = 38) and composed 97% of total prey items; Alaska Peninsula, AK (Sep–Oct), M. expansa found in 91% of stomachs (n = 53) and composed 85% of items, plus Mytilus edulis 32% of stomachs and amphipods 47% (REG).

Breeding. Chironomid larvae dominant prey item in stomachs of birds on Yukon-Kuskokwim Delta, AK (18–31 May, 73% of total prey items; 1–10 Jun, 97%; 21–30 Jun, 85%; 1–12 Jul, 75%), except for mid-Jun (11%); during mid-Jun, adult Diptera (50%) and adult Coleoptera (19%) important (Holmes 1970).

Wintering and Migrating. Winter and spring diets found to be similar (summarized by Stenzel et al. 1983). Arthropods, especially orders Tanaidacea and Amphipoda, figure prominently. At Bolinas Lagoon, CA, tube-dwelling amphipods (predominantly Corophium and Grandiderella spp.) found in >70% of stomach-pumped samples (n = 50); polychaetes (primarily Lumbrineris) in >20%. Alga-dwelling amphipods, bivalves, and gastrapods also found in significant amounts; trace amounts of small crustaceans, decapods, foraminifera, insects, and oligochaetes. At Cultus and False bays, WA, amphipods (Anisogammarus, Orchestoidea, Corophium, and Paraphoxus) most abundant prey (n = 34 stomachs; Couch 1966). Arthropods important at Humboldt, Bay, CA (Holmberg 1975), where of 15 stomachs, 25% contained Leptochelia dubia, 7% Anisogammarus pugettensis; other important prey items were bivalve Transennella tantilla (26% of stomachs) and Zostera seeds (33%). At each of 4 sites in coastal Washington, Corophium sp. accounted for 6–58% of total food items in esophagi and stomachs of 58 Dunlin; cumaceans (Leucon and Leptocuma spp.) found in 70% of samples from Bowerman Basin (but none elsewhere); a Tanaidacea (Pancolus californiensis) made up 1–14%; unidentified ostracods 1–14% (Buchanan et al. 1985a, Brennan et al. 1990).

At 2 areas in California, annelids were dominant prey items. Recher (1966) found that 70% of 46 stomachs of Dunlin from San Francisco Bay contained Neanthes succinea . In s. California, polychaetes (Streblospio, Polydorids) and oligochaetes found in all stomachs (n = 6) and in >75% of fecal droppings (n = 56) from Dunlin feeding in mixed mud-sand areas (Quammen 1984). Of 4 sites in w. Washington, annelids most abundant invertebrates available to Dunlin, but important prey item only at Kennedy Creek (76% of total prey items in stomachs of 13 birds) (Buchanan et al. 1985a, Brennen et al. 1990). At Hartney Bay, AK, polychaetes abundant, especially Nephtys ciliata, but not important in diet of migrating birds (Senner et al. 1989).

Bivalves, especially Gemma, Macoma, Mya, Mytilis, and Transsennella spp., important prey items at times for Dunlin in San Francisco Bay (Anderson 1970), Bodega Harbor (Ruiz 1987), and Humboldt Bay, CA (Holmberg 1975). At Hartney Bay, AK, Macoma balthica found in 91% of stomachs of migrating birds (n = 87); Mya sp. in 36%; Mytilus edulis in 18%; Clinocardium sp. in 13%; of all pelecypods, mean length consumed = 5.7 mm (± 0.3 SD, range 2–11, n = 71; Senner et al. 1989).

Outside breeding grounds, insects occasionally important. At Nisqually Delta, WA, Diptera larvae found in 60% of sampled Dunlin (Brennan et al. 1990). Hymenoptera the only food item found in 5 birds collected on Washington coast (Couch 1966). Dunlin feeding in salt ponds at San Francisco Bay, CA, ate 42% brine fly larvae (Ephydra cineria; Anderson 1970).

C. a. arcticola

Breeding. On breeding grounds by Barrow, AK, diet varies by age and season; insects (mainly tipulid and chironomid larvae) make up almost the entire prey base (Holmes 1966a). In early June, adults feed about 80% (measured as percent total food items in sample) on tipulid larvae (mainly Tipula carinifrons); by end of June to early July, switch to adult tipulid and chironomid larvae; by mid August, chironomid larvae use peaks (about 70%); and by the last week of August, about 50% tipulid larvae, 40% chironomid larvae, and 10% other eaten. 

In mid-June, newly hatched birds eat about 70% small adult insects (mainly chironomids), 20% adult tipulids, and 10% other; by early to mid-July, arachnids, adult Coleoptera, and chironomid larvae; early to late August, >80% chironomid larvae.  Difference in August diet between adults and immatures is explained by the movement of young to coastal and lakeshore areas where chironomid larvae are most abundant, while adults stay on upland tundra where tipulid larvae are the dominant prey (Holmes 1966a).

Little is known about the winter diet of this subspecies.

Other Foods

In Europe, gastropods (especially Hydrobia) are important prey (see Cramp and Simmons 1983); much less so in North America. Rarely feeds on small fish (e.g., Clevelandia ios; Warnock 1989). Plant matter and seeds occasionally eaten (Holmes 1970, Holmberg 1975, Stenzel et al. 1983, see also Cramp and Simmons 1983); may be more important than previously thought, especially in rice-producing regions such as Central Valley, CA and Gulf Coast states.

Adult, female, and juvenile Dunlin found to consume lemming (Lemmus trimucronatus) teeth and bones, presumably for calcium; females only consume teeth and bones in Jun, coinciding with egg-laying (MacLean 1974, see also Underhill 1994). Rehfisch (1994), using a basal metabolic rate (BMR) of 48.1 kJ day-1 bird-1 (from Kersten and Piersma 1987), calculated daily energy intake of Dunlin at Humber Estuary, England, to be 169.6 kJ day-1 bird-1.

See also Measurements: mass. In high winds, thermoregulation thought to be aided by roosting in large, compact flocks (Handel and Gill 1992). Lean dry mass and protein reserves in pectoral muscle correlated with midwinter air temperature, highest mass and protein reserves in colder areas (Davidson et al. 1986a, b). Lipid composition of leg tissue of Dunlin wintering in cold areas higher in unsaturated phosphoglycerides than of those wintering in warm climates; this may help maintain fluidity of cellular membranes in legs when in cold water or on ice (Pruitt et al. 1990).

Occasionally seen drinking brackish and salt water by poking bill into water and then tilting head back. In California, rarely seen to cast pellets (NDW).