A Revision of Lack's Brood Reduction Hypothesis

Abstract

A recent review by T. Amundsen and J. N. Stokland showed that, when food was plentiful, last-hatched nestlings of asynchronously hatched broods died more frequently than their nestmates or nestlings in synchronously hatched broods. They argued that if last-hatched nestlings die as a consequence of hatching asynchrony, then brood reduction must be maladaptive. I construct a model similar to a model by D. M. Temme and E. Charnov. In my model, asynchronously hatched broods experience reduced survival rates of the last-hatched nestling during good food years, and synchronously hatched broods experience entire brood starvation during bad food years. I compare the reproductive performance of parents raising an asynchronously hatched brood to parents raising a synchronously hatched brood. I show that hatching asynchrony is favored over synchronous hatching when good food years are not very frequent, when the survival rate of last-hatched nestlings during good food years is high, when the survival rate of nestlings raised in synchronously hatched broods during bad food years is low, or when bad food years are not severe. I discuss the model's assumptions and predictions, and I compare the results of this model to Temme and Charnov's model.