The Timing of Migration within the Context of an Annual Routine

We illustrate how a general technique for finding optimal cyclic routines can be applied to annual routines of migration. We present a schematic model in which there are two locations that differ in terms of food availability. We demonstrate how the model can be used to investigate the factors that determine the timing of migration. Reproductive values emerge from the model rather than being assumed. The form of the relationships between reproductive value and a bird's energy reserves and condition on the completion of the autumn migration is very different from that on the completion of the spring migration. The difference suggests that the timing of migration is more critical in spring than in autumn.