Metabolism of Avian Embryos: Patterns in Altricial and Precocial Birds

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Abstract
We measured rate of oxygen consumption of individual eggs in five species of birds. The pattern of oxygen consumption during development differs markedly between altricial and precocial species. The increased throughout incubation in eggs of the altricial species (Poephila guttata, Ploceus cucullatus, and Columba livia). In eggs of the precocial species (Coturnix coturnix and Anser anser) increased during the first 75% of incubation but then remained relatively constant until shortly before hatching. Growth patterns of embryos of Poephila and Coturnix differ in the same way as their patterns of oxygen consumption differ. We suggest that a decline in growth rate late in incubation results in the stabilization of in the precocial species. In growing embryos, increases with . The exponent is higher than that characterizing metabolism-mass relations of adult birds because of the energy demands of rapid embryonic growth. In both altricial and precocial species, eggshell conductance to gases is adapted primarily to regulate water loss and does not obviously limit of the embryo. The prior to pipping is more closely correlated with egg mass (and thus embryo mass) than with eggshell conductance. As a result, oxygen tensions in the air cells of Poephila and Ploceus eggs just prior to pipping are surprisingly low, only 72 and 85 torr, respectively.