He is a physiological ecologist whose research experience has ranged from energetics of burrowing by fossorial mammals, evolution of developmental patterns in birds, swimming energetics of marine iguanas and thermoregulation in insects. His research has dealt with energetics of alternative reproductive modes in reptiles and the adaptive significance of variation in water economy of developing reptile embryos. He collaborates with Carol Vleck on studies of the physiology of avian eggs, Adlie penguins, and the comparative biology of aging, especially in birds.