Food Habits

Figure 2. Least Sandpipers feeding on upper edge of mudflat with low vegetation

Feeding

Main Foods Taken

Benthic invertebrates (small amphipods, gastropods) and terrestrial invertebrates (dipterans). Tends to feed on most abundant prey of suitable size present (Couch 1966, Gratto et al. 1984).

Microhabitat For Foraging

In coastal areas, mainly on moist mud on broad mudflats or sparse cobble beaches, higher up on upper edge of mudflats and in openings of marsh vegetation (Fig. 2); generally farther from water’s edge than congeners (Manning 1952, Couch 1966, Recher and Recher 1969, Paulson 1993, JMC), although in a California estuary, fed mainly within 1 m of water’s edge (Colwell and Landrum 1993). Shallow water depth important habitat selection factor (Safran et al. 1997), rarely wades in water > 2–4 cm deep or forages on pure sand beaches (Colwell and Landrum 1993, Paulson 1993). In brackish California salt marshes, takes amphipods from algal mats and in sand (Page 1974). Density of prey (Corophium sp.) explains 53% of variation in microhabitat use, with higher percentage occurring in patches of mud with higher densities of prey (Colwell and Landrum 1993; see also Couch 1966). Forages more often in small muddy coastal bays than Western or Semipalmated sandpipers (Manning 1952, JMC, N. K. Dawe pers. comm.).

On marine coasts, timing and duration of foraging usually regulated by tidal cycles (Couch 1966, Baker and Baker 1973, Gerstenberg 1979, Robert et al. 1989), but an uncharacteristic lack of responsiveness to tidal cycles in some areas has been noted (Burger 1984: 7). Broad-based foraging niche, with large overlap with allopatric congeners on West Coast: Western Sandpiper (Couch 1966, Baldassarre and Fischer 1984 [71% overlap], Colwell and Landrum 1993 [90% overlap winter and summer]); Semipalmated Sandpiper and Dunlin (Couch 1966); but little overlap with Semipalmated Sandpiper or others species on East Coast (Recher 1966). In fall and winter in tropics, may forage more at night than during day (Robert et al. 1989). Foraging microhabitat diversity greater in summer than in winter (Baker and Baker 1973).

In inland wetlands, foraging confined entirely to moist or saturated muddy shorelines with shallow water up to 4 cm deep (Baldassarre and Fischer 1984, Hands et al. 1991, Skagen and Knopf 1994); chironimid pupae taken from surface at water’s edge or against algal mats (Brooks 1967). On coast, moves to inland flooded fields at high tide to feed in saturated ground on worms forced to surface by rain (Gerstenberg 1979).

No gross sexual habitat differences noted, but females have longer bills than males (about 2 mm longer) and so can probe deeper and feed on larger Corophium, which are present at greater depths on coastal mudflats (Gratto et al. 1984).

Food Capture And Consumption

Adults feed either by pecking at surface prey or probing for subsurface prey. In soft mud, generally probe for burrowing prey (Colwell and Landrum 1993). Foraging behavior more diverse in summer than winter (Baker and Baker 1973). In summer, adults decrease multiple pecks and increase single pecks, feeding at slower rate than in winter (Baker 1973). In winter, multiple pecks are most commonly used foraging technique; pecking rates faster than those of other calidridines (Baker and Baker 1973, Colwell and Landrum 1993). Detection of burrowing prey thought to be facilitated by Herbst corpuscles, mechano-receptors that can detect pressure gradients. They are located in ‘sensory pits’ under keratin layer of upper and lower mandible of bill (Nebel et al. 2005).

On intertidal mudflats in Washington, greatest amounts of food taken during first 3 h after low tide, with lesser amounts taken before low tide. Birds appear to peck mainly on middle and outer mudflats, but probe more often on inner flats (Couch 1966). Walk slowly while foraging.

Prefledgling chicks forage on small terrestrial prey by visual pecking. Probing in mud likely begins after fledging when chicks begin to venture away from heavily vegetated areas to feed (JMC).

Capable of ‘surface tension transport’ of prey, a feeding mechanism employing surface tensions of water surrounding prey to transport prey from bill tip to mouth. Using ‘surface tension transport’, Least Sandpipers moved prey faster than Western Sandpipers. Can also use tongue to slide prey backward against roof of mouth (‘slide and glue’ mechanism; Rubega 1997).

Diet

Major Food Items

Small amphipods, chironomids, dipterans, and isopods. During migration on a Washington estuary, mainly amphipods (Corophium spp.) on sandy substrates and Cyclorrapha and chironomid larvae on brackish silts; takes no molluscs, in contrast with Western Sandpipers (Couch 1966).

In California, amphipods Allorchestes angustus and Corophium spp. comprised 27 and 23% of diet, respectively, in salt marshes, whereas gastropods Lacuna and Phytia spp. were eaten heavily in nonmarsh habitat (Page 1974). In a California estuary, fed mainly on amphipod Corophium spp. but also on isopod Gnorimosphaeroma spp. and marine worms (Colwell and Landrum 1993). In California, migrants feeding in inland habitats take mainly ostracods (Recher 1964). In Bay of Fundy, Corophium volutator main prey of fall migrants (Hicklin and Smith 1979). During spring migration (May) in Delaware Bay, feeds on massive amounts of horseshoe crab (Limulus polyphemus) eggs (see Castro et al. 1989, Tsipoura and Burger 1999).

During fall migration in Illinois, benthic hydrophilids, chironomids, dipterans, corixids, and dytiscids, free-swimming dytiscids and hydrophilids, and surface insects, stratiomyids, and haliplids eaten; no plant matter (Brooks 1967). In Alabama, most migrants ate chironomid larvae and pupae, with some small beetles (Howell 1924).

During breeding season in n. Manitoba, feeds almost exclusively on larval dipterans, including larval chironomids, Psychodidae, Ceratopogonidae, tipulids, and dolichopodids (Baker 1977). On Pribilof I., 1 bird contained amphipods exclusively; another seeds of Hippuris vulgaris, hydroid stems, and chitin from Mytilus edulis (Preble 1923).

Quantitative Analysis

During migration, high dietary overlap on West Coast between Least and Western sandpipers (Couch 1966) and in interior between Least and Semipalmated and Stilt sandpipers (72% overlap), although Stilt Sandpipers fed mainly in habitat not used by Least Sandpipers (Baldassarre and Fischer 1984). In n. Manitoba, Least Sandpipers took smaller-sized prey than any of 9 other allopatric breeding shorebird species (including 3 Calidris species), with most prey being 0.2–0.6 mm in length (Baker 1977).

In Bay of Fundy, Sep juveniles ate mainly Corophium volutator (75% occurrence in 8 birds). One in 8 also contained gastropods, polychaetes, Gammarus lawrencianus and dipterans, respectively. Nine birds taken during fall migration contained by volume 88.6% Corophium volutator and 10.2% isopods (Hicklin and Smith 1979).

In ephemeral lakes of interior Texas, fall migrants fed on chironomid larvae (44% of stomach contents), seeds of marsh plants (19%), adult Coleoptera (13%), adult Diptera (11%), and larval Coleoptera (10%); mean prey size 4.81 ± 0.46 mm (n = 140) (Baldassarre and Fischer 1984). Consumed greater proportions of chironomids in spring than in fall, and greater proportions of hydrophilids in fall than in spring. Variety of seeds consumed in both season. Consumption of smartweed (Polygonum spp.) and panic grass (Panicum spp.) seeds increased from spring to fall. Selection of carabids, coenagrionids and cladocerans did not change between season (Davis and Smith 1998b).

Food Selection And Storage

Prey taken varies among regions and relative availability. Usually feeds on most abundant and available prey (Couch 1966, Gratto et al. 1984). Selects small prey compared to other shorebirds because of relatively short, narrow bill. In Bay of Fundy both sexes neglected any available prey longer than 6 mm, and females selected longer prey than males (4.10 ± 0.74 mm vs. 3.41 ± 0.96 mm), likely because of their longer bills (Gratto et al. 1984). However, during stop-over at Playa Lakes, Texas, analyses of stomach contents did not show difference in diet between males and females (Davis and Smith 1998b).

Slightly higher lipid reserves at a stop-over site in a wet than in a dry year (Davis et al. 2005).

Nutrition And Energetics

No data available. Average caloric content of common prey species was 15.1 J/mg dry weight and 17.2 J/mg dry weight for Corophium volutator < 4.5 mm and > 4.5 mm, respectively (Boates and Smith 1979); 20.0 kJ/g dry weight for chironomid larvae; 21.9–23.9 kJ/g dry weight for small diptera, tipulid, and coleoptera larvae (Custer in Ashkenazie and Safriel 1979).

Metabolism And Temperature Regulation

A model has been developed that estimates daily maintenance metabolic costs incurred on Arctic tundra. The model uses weather variables (temperature, wind speed, global solar radiation), morphological variables (body mass, diameter and height) and height of vegetation. Metabolic costs are most sensitive to changes in ambient temperature (Cartar and Morrison 1997).

Drinking, Pellet-Casting And Defecating

Few data available. As in other small shorebirds, fecal pellets are not likely useful in determining diet (see Schneider and Harrington 1981). Drinking not described, but 1 bird standing near its nest was observed sipping water from a tiny puddle atop a pile of cow manure (JMC).