Meeting Abstract

P2.52  Jan. 5  Population differences in the onset and rate of prebasic molt in Black-capped and White-eyed Vireos BUTLER, L K*; HAYDEN, T J; ROMERO, L M; Tufts University, Medford, MA; US Army Engineer Research and Development Center, Champaign, IL; Tufts University, Medford, MA luke.butler@tufts.edu

The post-breeding molt (prebasic molt) is an important stage in the annual cycle of small temperate birds, because failing to produce a complete set of high quality feathers probably has fitness costs. Birds that delay the start of molt consequently molt rapidly, and may produce low quality flight and body feathers. We compared the timing and rate of primary feather molt in two migrant passerines breeding sympatrically in central Texas (United States): the endangered Black-capped Vireo and the relatively common White-eyed Vireo. Within each species we compared molt in birds inhabiting a relatively secluded mixed juniper forest to birds inhabiting relatively open, brushy, secondary scrub near a road frequently trafficked by military and civilian vehicles. Black-capped Vireos from the open scrub area started primary molt later and completed molt faster than those from the juniper forest. White-eyed Vireos showed parallel but smaller differences between scrub and forest populations. Differences in the onset of molt between Black-capped Vireo populations could be habitat-driven, whereby adults cease breeding activities later in the scrub than the forest. Alternatively, stress caused by proximity to an active road could delay the physiological transition from breeding to molt.