The reliability of estimates of migration in the peppered moth Biston betularia and some implications for selection-migration models

Migration of adult males is one of the important variables involved in the mathematical models of industrial melanism in Biston betularia. Values for this variable are based on data from a capture-recapture performed by Bishop (1972) using both local and bred moths which were at least one night old at release. We carried out an experiment to compare the rate of recapture close to the point of release for moths allowed to fly away immediately after their emergence around dusk and those which were at least one night old at release. Unheld moths were less likely to be recaptured suggesting that males have an initial dispersal phase on their first night which results in a higher rate of emigration than on subsequent nights. Such a phase would have been largely missed in Bishop's experiment. The implications of this type of behaviour pattern for the models of spatial variation based on a selection-migration balance are discussed.