ARENS, J.R.; COOPER, S.J.; Univ. of Wisconsin Oshkosh; Univ. of Wisconsin Oshkosh: Ventilatory Adjustments to Cold Stress in Seasonally Acclimatized House Sparrows
Passerines that overwinter in temperate climates undergo seasonal acclimatization that is characterized by metabolic adjustments that may include increased basal metabolic rate (BMR) and cold-induced summit metabolism (Msum) in winter relative to summer. These changes in metabolism must be supported by equivalent changes in O2 transport. The first step in the O2 transport pathway is pulmonary ventilation. We examined ventilatory accommodation to changing oxygen demands in seasonally acclimatized house sparrows (Passer domesticus). We measured ventilation and oxygen consumption (VO2) in house sparrows under cold stress and thermoneutral conditions acclimatized to summer and winter conditions. Cold stress tests were conducted using a helox gas mixture of 79% helium and 21% oxygen. BMR and Msum increased significantly in winter compared to summer. Factorial increment in BMR was 1.63 and Msum was 1.29. Metabolic expansibility (Msum/BMR) was 9.0 in summer and 6.9 in winter birds. The metabolic expansibility of 9.0 in summer is the highest yet recorded for birds. Ventilatory accommodation was primarily due to changes in breathing frequency (f). Oxygen extraction efficiency was seasonally stable in thermoneutral and cold stress conditions. Breathing frequency under cold stress increased 2.22 times in summer and 1.97 times in winter compared to thermoneutral conditions. Tidal volumes also increased significantly under cold stress compared to thermoneutral conditions for both summer and winter birds. However, the only significant difference between summer and winter ventilation measures under cold stress was f. Mean f in cold stress for summer birds was 107 breaths per minute compared to 132 breaths per minute in winter birds.
