Oxygen deprivation (hypoxia) is a frequent fact of life for many animals, such as those that live at or visit high altitudes. Some champion bird species fly at altitudes where the oxygen supply is only one-fourth as high as at sea level and where daytime temperatures are often 50 degrees below freezing. The enormous oxygen requirement for flight (20 to 40 times higher than for resting) makes the feats of high-flying birds even more remarkable. For comparison, mammals including humans come down with mountain sickness at much lower altitudes, especially if they try to exercise. To understand physiological adaptations for flight and high-altitude tolerance in birds, my students and I study temperature regulation, energetics, cardiac and respiratory mechanics, oxygen and carbon-dioxide transport, and body-fluid volume regulation. We also investigate adaptations to hypoxia at the tissue and cell levels, especially in skeletal muscle, eye, and brain. For example, we have recently discovered a mechanism for supplementing the oxygen supply to the brain and retina of birds exposed to hypoxia. As part of an experiment on tissue hypoxia, we have found that the body tissues store huge quantities of body fluids, and birds therefore never suffer from shock. We do experiments on animals at rest, during flight in a wind tunnel, or during exposure to cold and artificial high altitude. To investigate why mammals do not tolerate hypoxia as well as birds, we also study the effects of hypoxia on the brains of rats, using changes in learning ability and memory, as well as histological and biochemical changes, as indicators. The long-term goal is to understand both the mechanism and the evolution of hypoxia tolerance. I welcome opportunities to work with students interested in animal adaptations to environmental stresses at the systems, tissue, and cell levels.

Vascular rete in the eye of a pigeon

Publications that represent the work I do: