Solitary Sandpiper

No other shorebird in North America nests in trees. The Solitary Sandpiper uses the abandoned nests of other passerine species rather than building its own — a strategy shared globally only with the Green Sandpiper (Tringa ochropus) of Eurasia, its ecological counterpart in the Old World. Favoured host species include American Robin, Rusty Blackbird, Canada Jay, Cedar Waxwing, Bohemian Waxwing, and Eastern Kingbird — all of which build sturdy, cup-shaped nests likely to survive a winter intact. The male identifies candidate nests; the female makes the final selection and modifies it by removing old lining and often relining with fresh material. Nests are typically placed in spruce or other conifers, sometimes in deciduous trees, at heights of 1.2–12 m (4–40 ft) above the ground, and up to 200 m from the nearest water.

The clutch consists of 3–5 eggs, usually 4. Eggs are pale greenish-white, heavily blotched and spotted with reddish-brown or purple markings, and measure approximately 3.4–3.9 cm long by 2.4–3.6 cm wide. Incubation lasts 23–24 days, with both parents sharing duties, though the precise division of labour is poorly documented. Only one brood is raised per year. Egg-laying begins in late May; in Ontario it may not begin until June.

Chicks are precocial — downy and mobile at hatching. Because the nest is elevated, chicks must jump or drop to the ground shortly after their down dries, then begin foraging independently while tended by one or both parents. Adults are not known to carry food to the young. The age at first flight is not well documented, reflecting how rarely active nests have been studied.

This tree-nesting strategy remained one of ornithology's great puzzles for nearly a century. Alexander Wilson described the species scientifically in 1813, but its nest went undiscovered for 90 years — until 1903. During that entire period, eggs and young of the Spotted Sandpiper were misidentified as those of the Solitary Sandpiper, a remarkable case of sustained ornithological confusion for one of North America's most widespread shorebirds.

Precise lifespan data for the Solitary Sandpiper are poorly known — a direct consequence of the species' solitary, dispersed habits, which make long-term individual tracking difficult. No specific maximum longevity record for this species appears in the USGS Bird Banding Laboratory database, and the species is not included in the EURING European longevity list. This is not unusual for a bird that breeds in remote boreal bogs, migrates alone at night, and winters scattered across tropical freshwater habitats from Mexico to Argentina.

Related Tringa sandpipers provide the best available comparison. The Wood Sandpiper (Tringa glareola) has a recorded maximum lifespan of around 11–12 years in Europe. The Common Greenshank (Tringa nebularia) has been recorded to at least 10 years. Based on these relatives, a wild Solitary Sandpiper likely lives somewhere in the range of 5–10 years under typical conditions, with exceptional individuals potentially reaching 10–12 years.

Mortality causes are not well documented but likely include predation during migration (raptors, particularly Peregrine Falcon and Merlin), nest predation on the breeding grounds, and the cumulative physiological costs of long-distance migration. The species' nocturnal migration strategy and preference for concealed, wooded wetland habitats may reduce predation pressure compared to shorebirds that migrate by day or roost on open mudflats. Climate-driven drying of boreal wetlands is a potential future threat to breeding success and, by extension, to population-level survival rates.

The Solitary Sandpiper is listed as Least Concern on the IUCN Red List (assessed 2018), with a global population estimated at approximately 190,000 mature individuals (Partners in Flight, 2023). The overall population trend is listed as unknown — not because the species is in obvious trouble, but because its dispersed, solitary habits make it almost impossible to census reliably. Available survey data from the 1990s show variability without a confirmed directional trend. Partners in Flight rates the species 10–11 out of 20 on the Continental Concern Score, indicating low to moderate concern. It is listed as a USFWS Bird of Conservation Concern and is protected under the Migratory Bird Treaty Act in the United States.

The greatest current threat is destruction and degradation of habitat on both breeding and wintering grounds. In the boreal zone, deforestation and logging — particularly in western Canada — are increasing pressures. Urbanisation, agriculture, and energy development across the boreal region raise further concern. Because 85–90% of the global population breeds within the Canadian boreal forest, the fate of this ecosystem is closely tied to the fate of the species.

Climate change poses a longer-term threat that may prove more significant than direct habitat loss. A warmer, drier climate could dry the small, shallow ponds and muskeg pools where the species breeds, fundamentally transforming its habitat. The species' dependence on beaver ponds and boreal wetlands — both sensitive to temperature and precipitation changes — makes it potentially more vulnerable to climate shifts than its current Least Concern status might suggest.

On the wintering grounds, the species' solitary and dispersed nature actually provides some protection: unlike gregarious shorebirds that concentrate on coastal mudflats, the Solitary Sandpiper is too spread out across tropical freshwater habitats to be significantly affected by hunting or localised habitat loss.

Two subspecies of Solitary Sandpiper are recognised, with distinct breeding ranges, migration routes, and subtle but consistent plumage differences. Tringa solitaria solitaria, the eastern subspecies, breeds from eastern British Columbia east to Labrador and Newfoundland and migrates largely east of the Rocky Mountains. Tringa solitaria cinnamomea, the western subspecies, breeds in Alaska and western Canada from northeastern Manitoba northwest to western Alaska, and migrates largely west of the Mississippi River. The two subspecies winter in different parts of Central and South America.

In the hand, the size difference is clear: female wing lengths average 140 mm in cinnamomea versus 132.5 mm in solitaria; male wing lengths average 134.65 mm versus 127.5 mm respectively. In the field, adults are difficult to separate, but juveniles are more straightforward. Juvenile cinnamomea shows buff-coloured spots on the upperparts (visible through September), lighter olive-brown tones overall, heavy mottling on the outer primary feathers, and narrower white bars on the tail. Juvenile solitaria has whiter spots, darker and more blackish upperparts, and broader white tail bars. Downy chicks of both subspecies are identical.

The western subspecies cinnamomea is the one most likely to produce vagrant records in western North America and, potentially, in the Pacific. The eastern subspecies is the one responsible for the occasional transatlantic vagrants that reach the British Isles, presumably carried east by autumn westerly winds during their southward migration — a route that mirrors the well-documented Atlantic crossing made by other American shorebirds such as the Buff-breasted Sandpiper and Pectoral Sandpiper.

The Solitary Sandpiper's courtship display is one of the more elaborate among North American waders, though it is rarely observed given the remoteness of the breeding grounds. Males arrive on territory in spring and begin displaying almost immediately. The primary aerial display involves the male rising slowly a few metres into the air on quivering, rapidly beating wings, with the tail spread so that only the white outer feathers are visible. He holds this hovering position while calling, then slowly descends to the same spot — a display that emphasises both the white tail pattern and the twittering song simultaneously.

Males also perform a slow, undulating hovering song-flight over the nesting territory, and call repeatedly from prominent perches at the tops of spruce trees. Before and after copulation, the male holds up a single wing — a brief but distinctive gesture. Copulation itself takes place near feeding locations rather than at the nest site, concentrated in a period of approximately five days before the first egg is laid.

Territories are large by sandpiper standards — up to 50 hectares (124 acres) — and males defend them against other males with persistent calling and aerial chasing. The female makes the final nest selection from candidates identified by the male, then modifies the chosen nest by removing old lining and adding fresh material. This division of roles — male prospecting, female deciding — is consistent with the reverse sexual size dimorphism of the species, in which females are measurably larger than males.