The peak load reduction hypothesis for avian hatching asynchrony

Summary According to the Peak Load Reduction Hypothesis, avian parents establish within-brood hatching asynchrony (via early incubation of first-laid eggs) in order to lower the maximum level of the brood's daily food demands. By offsetting the individual demand curves by a day or more, parents may be able to achieve adaptive levels of effort relief. We examined the potential parental savings from this strategy by developing a simple analytical model wherein individual offspring demand curves were either aligned (as in synchronous hatching) or displaced by a hatching interval variable (asynchronous hatching). Parental savings were calculated for various common brood sizes and hatching intervals.The results show that substantial savings can accrue to parents if both broods and hatching intervals are large or if individual demand curves rise to a high, narrow peak. However, the parameter values necessary for load reductions of even 5% appear seldom, if ever, met in nature. Unless very small savings have disproportionate value to parents, it seems unlikely that hatching asynchrony evolved because of its direct effects on trimming parental effort. The possibility remains open that adaptive levels of parental savings could result from a secondary interaction between a modest initial hatching interval and consequent competition among nestlings, which can greatly amplify the chicks' growth rate differences.