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 transport. 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 −12°C to 15.5°C in summer and 17.5°C in winter. Open-circuit respirometry was used to measure oxygen consumption (V̇O2) and ventilation was recorded using whole-body plethysmography. In both summer and winter, V̇O2 increased with decreasing Ta. V̇O2 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 (V̇I) 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 (V̇I) than rest-phase birds. Winter birds in their rest phase had significantly higher oxygen extraction efficiency (EO2) than active-phase birds. Winter birds at rest phase also had significantly higher EO2 than summer birds. Variación Estacional y Diaria en el Metabolismo y la Ventilación en Passer domesticus Resumen. Las aves paserinas que residen a lo largo del año en climas de la zona templada pasan por un proceso de aclimatación estacional que facilita el mantenimiento de su homeostasis termorregulatoria. Estos cambios en el metabolismo termorregulatorio deben estar apoyados por cambios equivalentes en el transporte de oxígeno. En este estudio medimos los efectos de la temperatura del ambiente y la hora del día sobre el metabolismo y la ventilación en Passer domesticus en verano e invierno. Las aves fueron expuestas a temperaturas ambiente (Ta) en un rango de −12°C a 15.5°C en el verano, llegando a 17.5°C en el invierno. Empleamos respirometría de circuito abierto para medir el consumo de oxígeno (V̇O2) y registramos la ventilación usando pletismografía de cuerpo entero. Tanto en el verano como en el invierno, V̇O2 aumentó con disminuciones en Ta. V̇O2 fue significativamente mayor durante la fase activa en comparación con la fase de descanso del ciclo di