Effects of an immune response on metabolism and ventilation in Black-capped Chickadees (poecile atricapillus) during cold stress
Black-capped chickadees (Poecile atricapillius) are small, non-migratory,passerine birds. Birds that are non-migratory that overwinter in cold, temperate regions have increased energetic costs due to thermoregulation during the winter. In addition, food availability may be lower, nighttime fasting is increased, and a decrease in foraging time may make it difficult to acquire the energy required for daily energy demands. If a bird were to develop an infection or acquire a parasite during these winter months, their ability to maintain their body temperature may be affected. The purpose of this study was to observe the effects of an immune response on both the metabolism and ventilation during acute cold exposure in seasonally acclimatized black-capped chickadees. Chickadees were captured using mist nets in summer months (June-August) and the winter (December). I measured BMR or Msum of chickadees injected with either phosphate buffered saline (PBS) or lipopolysaccharide (LPS). The BMR test used air and kept the chickadees at thermoneutral conditions, while the Msum test used a helox (~79% helium and ~21% oxygen) gas mixture to expose the chickadees to cold stress conditions. Open-circuit respirometry was used to measure oxygen consumption (V02), carbon dioxide production (VCO2), evaporative water loss (EWL) and ventilation. Thermal conductance, the temperature to become hypothermic or temperature at cold limit (Tcl), and evaporative water loss during Msum testing were found to be different between summer and winter caught birds. Metabolic rate and thermal conductance during BMR testing were found to be different between summer and winter caught birds. No difference was found for ventilation measurements in Msum testing. Breathing frequency for BMR testing was different between summer and winter caught birds, while oxygen extraction efficiency for BMR testing was different between phosphate buffered saline and lipopolysaccharide injected birds.