Migration of Bristle-Thighed Curlews on Laysan Island: Timing, Behavior and Estimated Flight Range

Abstract

Bristle-thighed Curlews (Numenius tahitiensis) fly at least 4,000 km non-stop from staging grounds in western Alaska to the northern edge of the winter range at Laysan Island in the Northwestern Hawaiian Islands. Adults migrate from Laysan in early May and return in July and August. Juveniles, which arrive in late August and early September, largely migrate unaccompanied by adults. Compared with other shorebirds, Bristle-thighed Curlews migrate in small flocks and show no diurnal pattern in timing of departures. Subadults do not fatten adequately for migration but often accompany departing adults briefly and then return to the island. Fat content in adults at the start of spring migration is high, averaging 42%. Our findings indicate that curlews wintering in the Central and South Pacific overfly Hawaii during spring and autumn, undertaking non-stop flights of >6,000 km. In the absence of tailwinds, only two of the four flight range models that we tested (Summers and Waltner 1979, Davidson 1984) provide reasonable estimates of the migratory performance of Bristle-thighed Curlews (i.e., non-stop flights from Alaska to Laysan and beyond). Within the range of altitudes at which they migrate, curlews probably seek out tailwinds that facilitate long-distance, non-stop flights.