Meeting Abstract
The climatic variability hypothesis posits that physiological flexibility should be higher in organisms from more variable climates. Summit (Msum) and basal (BMR) metabolic rates are flexible traits and seasonal metabolic flexibility can be advantageous for small birds living in highly seasonal environments. Behavioral thermoregulation may reduce demand for seasonal metabolic flexibility, but favorable microclimates may be less available to some birds than others, depending on habitat. To investigate the relationship between seasonal variation in environmental temperatures and metabolic flexibility, we compared seasonal metabolic flexibility and microclimates (operative temperatures) of horned larks (Eremophila alpestris), which occupy open habitats, and house sparrows (Passer domesticus), which occupy more protected habitats, from South Dakota. We hypothesized greater seasonal variation in BMR, Msum, and operative temperatures for horned larks than for house sparrows. Winter daily average and minimum operative temperatures were similar for the two species’ habitats, but including convection resulted in lower winter temperatures for lark habitats. Summer daily average and maximum operative temperatures were higher for lark habitats, even after incorporating convective heat loss. Both species demonstrated metabolic flexibility with higher Msum in winter and lower Msum in summer; however, the seasonal change for larks was 25% greater than in sparrows (39.4% vs. 31.4%). Significant seasonal variation in BMR occurred only for larks, with 92.5% higher BMR in winter than in summer. These results are consistent with the climatic variability hypothesis in that horned larks occupied habitats with more variable temperatures and showed greater seasonal metabolic flexibility.
