Body size and migration rate in moths

Migration rate is often thought to be affected by species distribution, abundance, body size, and niche width, but empirical results are controversial and fragmentary. In this study we examined these relationships in a large assemblage of noctuid moths. Migration rate was measured using two approaches, directly with a mark-recapture study in a network of small islands, and indirectly on the basis of the occurrence of moths outside their breeding habitat. The effects of the factors assumed to affect migration rate were adjusted for taxonomy using a simple yet novel approach based on logistic regression. Both with and without adjusting for taxonomy, the results indicate that abundance and body size influence migration rate, that the effects of abundance and body size have a negative interaction, and that the effects of ecological specialization on migration rate are evident (monophagous species migrate less than oligophagous or polyphagous species). The incidence of island or habitat patch occupancy was not affected by body size, most likely because body size has several contrasting consequences on the processes that determine island occupancy. Migration rate appears to be an evolutionarily labile character, which can readily transform in different phylogenetical lineages of moths.