Sharp-tailed Sandpiper

Sharp-tailed Sandpipers are omnivorous, though invertebrates dominate the diet throughout the year. Aquatic insects and their larvae are the primary food source, supplemented by molluscs (including bivalves and snails), crustaceans such as shrimps, worms, and occasionally seeds and other plant material. The precise composition shifts with season and habitat: on the breeding tundra, terrestrial invertebrates are most important; on migration and in winter, aquatic prey predominates.

Foraging is primarily visual — birds peck and jab at the surface with rapid, shallow movements, picking off prey items from mud, wet grass, or shallow water. Soft substrate is targeted with rapid probing bill movements when buried invertebrates are the goal. On coastal mudflats, birds work the surface systematically before moving inland to wade the shallow margins of freshwater wetlands as the tide rises. After rain, birds have been recorded foraging in paddocks of short grass well away from any water, presumably targeting earthworms or surface invertebrates flushed to the surface.

The species also forages on dry or wet mats of algae, among rotting seaweed or seagrass on beaches, and on the edges of stony wetlands and exposed reefs — a dietary flexibility that helps birds exploit whatever food source is locally abundant. In Alaska, juvenile birds feed intensively during the pre-migratory fattening period, with some individuals doubling their body weight before departing on the trans-Pacific crossing. The fuelling rates achieved there are thought to be significantly higher than at alternative staging sites, which may explain why juveniles make the seemingly counterintuitive detour east before heading south.

Sharp-tailed Sandpipers are gregarious birds, typically foraging in flocks that can number in the hundreds, though these often fragment into scattered, loosely associated groups spread across a wetland. When feeding, birds frequently crouch low — a posture thought to reduce their visibility to aerial predators. Despite this wariness, the species can be surprisingly confiding around humans, sometimes allowing close approach at favoured wetland sites.

While foraging, the Sharp-tailed Sandpiper bobs its head and rear end — a behaviour shared with several other Calidris sandpipers. Foraging activity shifts with the tide: at low water, birds work intertidal mudflats; as the tide rises, they move inland to freshwater wetlands. This tidal rhythm is well documented at Australian coastal sites where the species winters in large numbers.

On the Siberian breeding grounds, males are highly territorial and vocal, performing elaborate aerial and ground displays to attract females. The mating system is polygynous — and possibly promiscuous — with males attempting to mate with multiple females entering their territory. Once mating is complete, males depart the breeding grounds during incubation, leaving all parental duties to the female. This means that by the time juveniles are preparing for their first migration, their fathers have already been gone for weeks.

An interspecific behaviour documented on the breeding grounds reveals a striking spatial relationship with the Pectoral Sandpiper: Sharp-tailed Sandpipers maintain a minimum nesting distance of at least 33 metres from Pectoral Sandpiper nests, even though the two species' territories overlap extensively. This spatial avoidance — apparently to reduce competition between two ecologically similar species — does not apply to other shorebird neighbours. This makes it a rare and well-documented example of interspecific territorial partitioning.

A sharp whit-whit rising from a wetland margin is often the first sign that Sharp-tailed Sandpipers are present — the species' characteristic flight call, frequently doubled and given at take-off, where it is sometimes rendered as trit-trit. A softer trreep is also described, and in flight birds give soft twitters and a more melodious trrrt wiitiit that has been compared to certain calls of the Barn Swallow — an unexpected sonic reference for a wader.

The song, delivered on the breeding grounds, is unlike that of any other Calidris sandpiper. It includes a long, muffled trill and a low-pitched, aspirated hoop. During the male's aerial display flight, the inflated breast sac produces a dry, crackling warble — a sound generated by the sac itself rather than the syrinx, functioning as an acoustic advertisement of male quality that carries across the open tundra. During ground display, the male produces clicking notes in time with rapid wing-flicking movements, creating a percussive accompaniment to the visual performance.

An aggressive call used in antagonistic encounters between Sharp-tailed Sandpipers has also been recorded, distinct from the flight and display vocalisations. Males are most vocal on the breeding grounds during the courtship period in June and July. Outside the breeding season, the species is generally quieter, though the characteristic flight call is regularly given by migrating and wintering birds and is often the first indication of the species' presence at a wetland site.

Swift, direct, and capable of sustained overwater flight lasting days, the Sharp-tailed Sandpiper is built for distance rather than spectacle. The wings are moderately long and pointed, producing a streamlined silhouette, with rapid, fairly shallow wingbeats typical of the Calidris sandpipers. The narrow white wingbar — formed by the white tips of the greater and primary coverts — is visible in flight but less bold than in some related species. The white sides to the rump are visible as the bird banks, contrasting with the dark central rump and uppertail-coverts.

The wedge-shaped tail with pointed central rectrices is the species' namesake feature and can be seen at close range in good light, though it requires a direct view of the tail to appreciate. The pot-bellied body shape gives the bird a slightly front-heavy look in flight compared to slimmer waders such as the Wood Sandpiper.

When flushed, birds typically rise steeply and call loudly — the sharp whit-whit flight call is often the first indication of the species' presence. Migrating flocks of up to several hundred birds fly in loose, shifting formations rather than tight coordinated groups. The trans-Pacific migration undertaken by juveniles — a non-stop flight of up to 9,800 km — represents one of the most demanding overwater crossings of any small shorebird, requiring sustained flight over open ocean for days without rest or feeding.