Postnuptial and Postjuvenal Molt in White-Crowned Sparrows in Central Alaska

Abstract

Breeding of migratory birds at high latitudes involves problems of allocation of time and energy among the functions of migration, reproduction itself, and molt. Indeed, in some species, notably swallows and flycatchers, the timing system that has evolved defers the postnuptial molt entirely or mainly until after the southward migration (Johnson 1963). In some populations or species, as in Zonotrichia leucophrys gambelii (Farner 1964), these three functions are sharply partitioned temporally through the course of the late spring and