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Bristle-thighed Curlew
Numenius tahitiensis
Order
CHARADRIIFORMES
– Family
SCOLOPACIDAE
Authors: Marks, Jeffrey S., T. Lee Tibbitts, Robert E. Gill, and Brian J. Mccaffery

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Introduction

Adult Bristle-thighed Curlew, Anchor Point, AK, 20 May.
Figure 1. Breeding distribution of the Bristle-thighed Curlew.

[The occurrence of this specimen] . . . in a locality [Alaska] so remote and so unlike its natural haunt [Oceania] , can only be regarded as being something purely accidental.

Baird, Brewer, and Ridgway 1884,

The Water Birds of North America

At the time The Water Birds of North America appeared, only two Bristle-thighed Curlews had been collected outside of Oceania, one in 1869 and the other in 1880. Both were taken in Alaska in May, and only the 1869 record was known to the Water Birds authors. Perhaps as a sign of the times, the idea that this first Alaskan record represented anything other than a vagrant was not considered by Baird and his colleagues. Indeed, not until the end of the 19th century did ornithologists accept Alaska as a likely breeding ground for the Bristle-thighed Curlew, and another 50 years would pass before the curlew finally gave up its nesting secret. With the discovery of a nest north of the lower Yukon River in 1948 by David Allen and Henry Kyllingstad, the Bristle-thighed Curlew became one of the last North American birds to have its nest and eggs described. We now know that this species nests in remote tundra in two areas of western Alaska and winters on atolls and small islands in Oceania. Intensive efforts to study this bird year-round were initiated in the late 1980s. Surveys of suitable habitat in the two breeding areas yielded an estimate of fewer than 3,500 breeding pairs; including subadults that over-summer in Oceania, the total population probably does not exceed 10,000 birds.

In its biology and behavior, the Bristle-thighed Curlew is one of the most unusual of all shorebirds. It is the only migratory shorebird that winters exclusively on oceanic islands and the only shorebird known to become flightless during molt and to use tools when foraging. Like only a handful of other species, it takes on huge fat stores to fuel long nonstop flights over open ocean and reduces the size of its nutritional organs in preparation for these flights. The species’ English name refers to the elongated bare shafts of the thigh feathers; the function of these unique feathers remains a mystery.

All Bristle-thighed Curlews fly at least 4,000 km nonstop between Alaska and the northern end of the winter range in the Northwestern Hawaiian Islands. Studies of marked birds on Laysan Island revealed that curlews wintering in the Central and South Pacific overfly the Northwestern chain during spring and fall migration, making nonstop flights in excess of 6,000 km twice each year. Thus, along with Bar-tailed Godwits (Limosa lapponica), Bristle-thighed Curlews make one of the longest nonstop flights known for any bird. Adults arrive on breeding grounds in early to mid-May. Males defend large territories (up to 275 ha) using spectacular aerial displays that involve complex vocalizations. Both parents care for their chicks for a few weeks, after which most depart and leave their broods in aggregations that are tended by small numbers of adults. Successful adults abandon breeding grounds in July or August to stage along the Alaskan coast, where they fatten on fruits that provide the energy to fuel southward migration. Juveniles head for the staging grounds slightly later than adults and leave Alaska from mid-August to early September, unaccompanied by their parents. Although its tundra breeding grounds have remained largely undisturbed, the Bristle-thighed Curlew probably suffers from predation by exotic mammals on its oceanic wintering grounds. Thus, its numbers may be declining, although data on population trends are lacking.

Aside from brief reports on the species’ presencein Oceania and Alaska, little was published on the biology of Bristle-thighed Curlews before 1986. Notable exceptions include a thorough overview of muse-um specimens that resulted in an accurate depiction of the winter range (Stickney 1943); the first description of the nest, eggs, and downy young (Allen 1948, Kyllingstad 1948, Allen and Kyllingstad 1949); the first evidence for molt-induced flightlessness (Kinsky and Yaldwyn 1981); and a series of papers on physiology and molt of oversummering birds in the Marshall Islands (Johnson 1973, 1977, 1979; Johnson and Morton 1976). Various aspects of breeding biology were revealed in the works of McCaffery and Peltola (1986), Gill et al. (1991), McCaffery and Gill (1992), and Lanctot et al. (1995). The only thorough treatment of curlews on the Alaskan staging grounds came from Handel and Dau (1988), and myriad aspects of the species’ ecology on the wintering grounds were uncovered by Marks et al. (1990), Gill and Redmond (1992), Marks (1993), and Marks and Redmond (1994b, 1996).

Below, observations from the southern breeding population on the Yukon-Kuskokwim Delta (hereafter Yukon Delta) refer to the southern Nulato Hills study area of BJM (including Curlew Lake and Allen Creek), and those from the northern breeding population on the central Seward Peninsula refer to the Neva Creek study area of REG and TLT.