The general problems presented by terrestrial environments are carried to extremes by subtropical deserts, which are notable for their high temperatures and their capacity to desiccate organisms. Traditional views suggest that small insectivorous birds encounter little difficulty in maintaining water balance because of the high fractional hydration of their prey. There is remarkably little direct evidence to support this view; water balance in small insectivorous birds exposed to environmental conditions normally prevailing in subtropical deserts is essentially unknown. Recent analyses, however, suggest that even under cool conditions, small birds may show either a water deficit or barely balance their water budgets over the daily cycle. This research focuses on (a) the physiological and ecological bases of the suppression of vital activities by a very small, diurnal bird, the Verdin, during the hottest portions of the summer day in the Sonoran Desert, and (b) dissecting the physiological foundation for occupancy of this most extreme terrestrial habitat by developing a complete water budget for animals exposed to ecologically realistic conditions. This project will examine Verdin daily activity patterns, microclimate selection, avenues and rates of water intake and loss, field metabolic rates, patterns of resource utilization and resource availability and abundance.
