New specimens freom Sinaloa, Mexico, as well as two older specimens, show that both adult and recently fledged Lucy's Warblers (Vermivora luciae) often move far south of their breeding grounds to molt in the tropical deciduous forests of northwestern Mexico. Remarkably, the first preformative (= first prebasic) molt is complete in Lucy's Warblers, including the replacement of flight feathers, primary coverts, and rectrices
thus, previous aging criteria based on the wear and appearance of these feathers are invalid. We suggest that the recent conclusion that Lucy's Warblers molt on their breeding grounds (Voelker and McFarland 2002) is an artifact of more collecting in the southwestern United States than in western Mexico during late summer. An index of relative collecting in Mexico and the United States, as well as data freom constanteffort mist netting, suggest that most Lucy's Warblers move south to molt.
