Latitudinal variation in the definitive prebasic molt of Yellow Warblers

We compared the definitive prebasic molt schedules of Yellow Warblers (Dendroica petechia) at two northern temperate breeding sites: the Vermont Institute of Natural Science (Vermont) in Woodstock, Vermont, and North Point (James Bay) on the southwestern coast of James Bay, Ontario. The two sites are separated by 8° of latitude. Yellow Warblers initiated molt significantly earlier in Vermont than at James Bay, with respective mean onset dates of 29 June and 20 July, but durations and rates of molt did not differ significantly between populations at the two sites. Mean individual molt durations spanned 44.5 days in Vermont and 40.0 days at James Bay. Molt rate of females differed significantly between the two sites, but male rates were similar. Based on number of primaries growing simultaneously, Yellow Warblers in both Vermont and James Bay appear to undergo a rapid and intense molt. The earlier and slightly more protracted molt of Yellow Warblers in Vermont may result from their earlier spring arrival and longer breeding season. Received 22 November 2002, accepted 11 March 2003.
Migratory birds that breed in seasonally variable environments typically partition reproduction, molt, and migration within their annual cycles. Energy resource conflicts are minimized by the temporal segregation of such events [...]