Meeting Abstract
The evolution of major body plans requires remodelling not only of external features, but also of internal physiology. The evolution of body plans in birds has led to a variety of body plans required for optimizing flight costs, and presumably similar changes have occurred at the level of oxygen carrying capacity to achieve the oxygen demands required for various flight styles. To examine the evolution of oxygen capacity among birds, we analyzed hematocrit (packed cell volume) values from 1547 studies including 238 species from all extant avian orders, as hematocrit is widely measured as an index of oxygen carrying capacity. Hematocrit was highest in specialist flyers, followed by divers, non-specialist fliers and runners. Among non-specialist flyers, hematocrit varied with relative flight costs. Furthermore, bird order, representing large variation in body plans, explained more variation than species or genus. Residual inter-specific variation was associated with age, infection status and captivity, not sex or season. We concluded that the evolution of flight styles among avian orders required remodeling of oxygen carrying capacity. Furthermore, use of hematocrit for conservation physiology should rely on data from similar studies (captivity, age, infection status), but data from other species under similar conditions within the same genus are likely comparable.
