Thermal acclimation in a small Afrotropical Bird

Wild-caught animals are regularly used in physiological studies, yet the length of time it takes for completion of their acclimation to laboratory conditions remains largely unknown. In particular, Afrotropical species are relatively understudied compared with temperate and Holarctic species. Thus, we measured a number of metabolic variables in a 10g Afrotropical bird, the Cape White-eye (Zosterops virens), at weekly intervals, over an 8-week period, while birds were acclimating to two different constant thermal environments; 25°C and 29°C. Body mass increased significantly in the first three weeks, remaining approximately constant thereafter, with no significant difference between birds housed at 25°C and those housed at 29°C. However, whole animal resting metabolic rates remained constant throughout the eight-week study period, with values for birds housed at 29°C lower than for birds housed at 25°C. Rather than pointing to a minimum time period necessary for thermal acclimation, these results suggest that in some instances, freshly wild-caught small passerines may not need to be acclimated to laboratory conditions or respirometry equipment, prior to measurements of their resting metabolic rate.