The Seasonality of Metabolic Strategies in Anna's Hummingbird (Calypte anna)
Chelsea B. Johnson, Sam M. Sandoval, Jesus R. Ovalle
Department of Biology
Faculty Supervisor: Derrick JE Groom
Energy demands vary seasonally as environmental conditions change and animals enter different life history stages, such as breeding and migration. To meet these fluctuating energy needs, animals must adjust both energy intake and expenditure via foraging, activity, and metabolism. However, our knowledge regarding energy balance strategies remains poor. Hummingbirds have among the highest metabolic rates of any vertebrate. The objective of this project is to characterize the seasonality of metabolic strategies in captive Anna’s hummingbirds (Calypte anna). We hypothesized that hummingbirds would modify their metabolic phenotypes in accordance with the annual cycle. Data was collected for four weeks each across three seasons: summer long days, fall equinox, and winter short days. Food intake was measured daily, basal metabolic rate (BMR) and body mass were measured weekly, and torpor use was estimated using thermal imaging. Both food intake and BMR decreased as days shortened, while body mass decreased from summer to fall but increased in winter. Preliminary results show that the number of individuals observed using torpor increased from summer to fall. These results suggest hummingbirds change their metabolic strategies seasonally. As environmental conditions shift, studying these patterns can help shed light on resource requirements and habitat suitability across the year.