BREUNER, CW*; CORNELIUS, JM; HAHN, TP; Univ. of Texas at Austin; Univ. of California Davis; Univ. of California Davis: Androgens and arrival biology in a migratory songbird

Seasonal breeders rely on photoperiod to initiate breeding. However, local conditions can modulate the timing of nesting onset. One important component of reproductive development affected by local conditions is androgen secretion in males. We examined patterns of androgen secretion during the arrival phase of the breeding season in a moderately long-distance migrant, the mountain white-crowned sparrow (Zonotrichia leucophrys oriantha). Our study population breeds just outside Yosemite Park (~3000 m elevation). Males may begin defending territories immediately upon arrival (early May) or as late as mid June (depending on residual snow pack, weather). During unsettled weather in May, sparrows may be up at the breeding site or at lower elevation staging areas nearby. In 2005, early May snow-pack was 150% of the long-term average, and onset of nesting was late. We collected plasma samples from three groups of males: 1) sparrows at low elevation staging areas, 2) high-elevation sparrows caught on or near their eventual breeding territories, and 3) high-elevation sparrows that were transients at the capture site. Samples from the same time window for all three groups show that low elevation sparrows have significantly lower androgen levels than high-elevation sparrows on their breeding territories. However, transient males at high elevation had intermediate levels between the two groups (and not significantly different from either). Mountain white-crowned sparrows do not modulate androgens in response to male-male interactions; as such, these data suggest that the breeding site itself, not elevation, temperature, or the presence of competing males is one of the more important local cues. We are currently measuring corticosterone and corticosteroid binding globulin levels from the same samples to estimate free testosterone levels.