THE PHYSIOLOGICAL-BASIS OF DIVING TO DEPTH - BIRDS AND MAMMALS

There is wide diversity in the animals that dive to depth and in the d istribution of their body oxygen stores. A hallmark of animals diving to depth is a substantial elevation of muscle myoglobin concentration. In deep divers, more than 80% of the oxygen store is in the blood and muscles. How these oxygen stores are managed, particularly within mus cle, is unclear. The aerobic endurance of four species has now been me asured. These measurements provide a standard for other species in whi ch the limits cannot be measured. Diving to depth requires several ada ptations to the effects of pressure. In mammals, one adaptation is lun g collapse at shallow depths, which limits absorption of nitrogen. Blo od Nz levels remain below the threshold for decompression sickness. No such adaptive model is known for birds. There appear to be two diving strategies used by animals that dive to depth. Seals, for example, se ldom rely on anaerobic metabolism. Birds, on the other hand, frequentl y rely on anaerobic metabolism to exploit prey-rich depths otherwise u navailable to them.