Moult and Moult Migration in a Transequatorially Migrating Shorebird: Wilson's Phalarope

Abstract

In autumn, adult Wilson's Phalaropes congregate at Mono Lake, California, and other hypersaline lakes in the Great Basin of the western United States, where they moult and stage before migrating to South America. In 32-40 days some adults replace the entire body plumage, the rectrices, and several primaries. This phase of the moult, which is accomplished more quickly than in other waders, is facilitated by the abundant invertebrate resources in Mono Lake and probably by the prevailing warm temperatures. Primaries are moulted and replaced singly, insuring that the wing surface will be nearly intact whenever the birds accumulate sufficient fat to begin their non-stop migration to South America. The prebasic moult is resumed on the wintering grounds and is completed in January, when the prealternate moult of the rectrices commences. The Wood Sandpiper is the only other wader for which a moult migration has been demonstrated convincingly.