BIRDS CONSERVE PLASMA-VOLUME DURING THERMAL AND FLIGHT-INCURRED DEHYDRATION

Dehydration tolerance in mammals is associated with the degree to whic h an animal is able to maintain plasma volume. During thermal dehydrat ion, rock pigeons (Columba livia), quail (Coturnix coturnix japonica), and white-necked ravens (Corvus cryptoleucus) maintained nearly const ant volumes despite mean body mass losses of 17%, 15%, and 13%, respec tively. During flight-incurred dehydration in tippler pigeons (C. livi a), no changes occurred in plasma volume although the birds lost 6%-10 % of their preflight body mass. Thus, dehydrated birds were found to b e excellent plasma volume conservers, like the most xeric-adapted mamm al species. We suggest that plasma volume conservation in birds is an adaptation associated with high beat loads incurred during flight. In contrast, plasma conservation in mammals is associated with their abil ity to inhabit arid environments.