Metabolism of Avian Embryos: Ontogeny and Temperature Effects in the Ostrich

In the first comparative consideration of the metabolism of avian embryos, Rahn et al. (1974) made several important assumptions and offered a number of interesting predictions. One of their assumptions was that the relation between metabolic rate and incubation age (days incubated) is the same in all avian species as it is in the chicken (Gallus gallus). A second important assumption was that the partial pressures of oxygen and carbon dioxide in the air cell during the plateau phase are essentially the same in all species, regardless of egg mass and incubation period. This assumption led Rahn et al. to predict that, for eggs of different species but of the same mass ( W), “plateau” metabolic rate (I&,) * is inversely related to the length of the incubation period (I) and can be predicted most accurately from the equation: