Thermoregulation and Oxygen Consumption during Terrestrial Locomotion by White-Crowned Sparrows Zonotrichia leucophrys gambelii

Abstract

We trained white-crowned sparrows to locomote (normal mixed gait) on the wiremesh substrate of a circular treadmill while we measured steady-state $\dot{V}O_{2}$, evaporative water loss ($\dot{m}_{v}$), and intraperitoneal temperature ($T_{b}$) at several treadmill speeds (0, 0.30, 0.35, 0.41, 0.46 km h⁻¹) and air temperatures ($T_{a}$, 10, 0, 12, and 25 C) at each speed. In birds at rest, $T_{b}$ increased as $T_{a}$ diminished, but $T_{b}$ was independent of $T_{a}$ when birds were locomoting. At any $T_{a}$, $T_{b}$ increased linearly with treadmill speed (to a maximum of 44.1 C). At $T_{a} = 12 C$ or lower, $\dot{V}O_{2}$ was a linear function of $T_{a}$ at all treadmill speeds but did not conform to this regression at $T_{a} = 25 C$ ($\dot{V}O_{2}$ at 0.35-0.46 km h⁻¹ was lower than expected). We hypothesize that $T_{a}$ is not a reliable index of thermal environment in this zone and should be replaced by the operative temperature, $T_{e}$. At all $T_{a}'s$, $\dot{V}O_{2}$ was a linear function of ...