SEASONAL AND GEOPGRAPHICAL VARIATION IN DOWNY WOODPECKER (PICOIDES PUBESCENS) METABOLISM AND THERMOREGULATION

Abstract

Downy woodpeckers (Picoides pubescens) are small, non-migratory, nonpasserine birds. Non-migratory birds that overwinter in cold temperate zones are exposed to energetically costly conditions during winter. These conditions include decreased daytime for foraging, long nights requiring increased periods of fasting, and decreased food availability. These birds will also be exposed to extremely cold temperatures in winter months. To survive these conditions birds must go through a process of season acclimatization. In birds, seasonal acclimatization has been found to mainly focus on adjustments in metabolic rates such as basal metabolic rates (BMR) and summit metabolic rates (Msum) when under cold stress. Another possible factor in seasonal acclimatization is the substitution of heat produced from locomotive muscle activity for thermoregulatory heat. Despite the impact that metabolic rates have been shown to have on seasonal acclimatization, there has been little research into geographic variation in metabolic rates and ventilation of birds. The purpose of this study was to observe seasonal variation in metabolic rates and ventilation variables between Wisconsin Downy woodpeckers and South Dakota Downy woodpeckers. A secondary goal of this study was to observe seasonal variation in thermoregulatory substitution in Wisconsin Downy woodpeckers. Open-circuit respirometry was used to measure oxygen consumption (VO2) and ventilation in seasonally acclimatized Downy woodpeckers. Metabolic rates and ventilation were measured under cold stress using a helox (~79% helium and ~21% oxygen) gas mixture and at thermoneutral zone (TNZ) conditions. Foraging activity was also measured using an infrared camera and a closed-circuit television monitor. During foraging trials activity was measured by time spent foraging on a peanut feeder placed into the metabolic chamber. Heat of activity was measured using a thermocoupler when birds were foraging and when feeders had been removed and birds were at rest. Wisconsin Downy woodpeckers showed a significantly higher BMR and Msum in winter compared to summer. South Dakota Downy woodpeckers had a significantly higher Msum in both summer and winter compared to Wisconsin Downy woodpeckers. Wisconsin Downy woodpeckers had significantly higher EO2 in the winter compared to summer during both BMR and Msum testing. Thermoregulatory substitution was observed in Wisconsin Downy woodpeckers during summer.