SEASONAL AND DIURNAL VARIATION IN METABOLISM AND VENTILATION IN HOUSE SPARROWS

Passerines that are year-round residents in temperate climates undergo seasonal acclimatization that facilitates maintenance of thermoregulatory homeostasis. These changes in thermoregulatory metabolism must be supported by equivalent changes in oxygen trans- port. We measured the effects of ambient temperature and time of day on metabolism and ventilation in House Sparrows (Passer domesticus) in summer and winter. House Sparrows were exposed to ambient temperatures (Ta) ranging from 2128C to 15.58C in summer and 17.58C in winter. Open-circuit respirometry was used to measure oxygen consumption (VO2) and ventilation was recorded using whole-body plethysmography. In both summer and win- ter, VO2 increased with decreasing Ta .VO2 was significantly higher during the active phase compared to the resting phase of the daily cycle in both summer and winter. Thermal conductance was significantly lower in nighttime birds compared to daytime birds. With increased oxygen demands, minute volume (VI) increased in both summer and winter. In summer, only respiratory frequency (f) was significantly affected by time of day. In winter, active-phase birds had significantly higher respiratory frequency and minute volume (VI) than rest-phase birds. Winter birds in their rest phase had significantly higher oxygen ex- traction efficiency (EO 2) than active-phase birds. Winter birds at rest phase also had signif- icantly higher EO2 than summer birds.