The Optimization of Growth Rate in Altricial Birds

Abstract

I have developed models relating the rate of growth of altricial birds to annual production of fledglings, a measure of evolutionary fitness. In the models, growth rate influences production through its effect on the power requirements of the nestling and the length of the nesting cycle; the latter in turn affects probability of survival to fledging and number of broods reared per year. The models were evaluated to determine whether empirically reasonable estimates of power requirements and nesting mortality resulted in predicted optimum growth rates within the range of observed values. By and large the models were successful. They do not adequately explain the reduced growth rates of tropical altricial species compared to their temperate—zone counterparts. Moreover, they do not address the phenomenon of slow growth in self—feeding, precocial species. But the confirmation of the model for many altricial birds suggests that it may be possible to understand interspecific variation in growth rates as the result of adaptations to levels of predation and the requirement for, availability of, energy to the nestling.