Meeting Abstract

P3.169  Tuesday, Jan. 6  Relationships between corticosterone concentrations and the onset, progression, intensity, and rate of molt in two free-living birds BUTLER, L.K.*; ROMERO, L.M.; Tufts University; Tufts University luke.butler@tufts.edu

The post-breeding (prebasic) molt in birds is typically correlated with a drop in baseline and stress-induced concentrations of the primary avian glucocorticoid, corticosterone (CORT). However, to our knowledge, details of the relationships between CORT and molt onset, molt progression (the stage of molt), molt intensity (the number of growing feathers), and molt rate (the speed with which molt is completed) are unknown for any free-living bird. We investigated these relationships in two seasonally-breeding songbirds, the Black-capped Vireo (Vireo atricapilla) and the White-eyed Vireo (V. griseus), on their breeding grounds in Texas, USA. We detailed the timing, progress, intensity, and rate of molt in two populations of each species, and correlated these parameters with baseline and stress-induced CORT concentrations. CORT concentrations started to decline weeks before the onset of molt, were lowest near the onset of molt, and varied little with molt intensity, progress, or rate. These results do not contradict the widely held idea that CORT is lower during molt in order to avoid CORT’s negative effects on protein synthesis (i.e., feather production), but the lack of a close temporal connection between the seasonal decline in CORT and the onset of molt, and the lack of strong relationships between CORT concentrations and the intensity, progression, and rate of molt, suggest that the seasonal decline in CORT concentrations in temperate birds may have other functions as well.