Global warming and avian occupancy of hot deserts; a physiological and behavioral perspective

Avian adjustments to desert environments are characterized by an integration of behavior and physiology. These responses serve to maintain homeostasis and conserve vital resources such as water. The small size of birds confers a close coupling to the thermal environment and demands rapid adjustments to environmental challenges. Physiological responses to heat stress include hyperthermia, and increased evaporative cooling as environmental temperatures approach body temperature. Behaviorally, desert birds respond to heat stress by drastically reducing activity during the hottest parts of the day and selecting cool shaded microsites. This characteristic behavioral response presents a potential problem in the face of global warming. If birds totally forgo foraging during extremely hot periods, increased evaporative water loss rates due to higher environmental temperatures could lead to significant episodes of direct mortality for birds in these regions. A simple model is presented which integrates behavior and physiology to predict survival times based on dehydration tolerance, microsite selection and environmental temperature.