Abstract

(1) The diet of the bat Rhinolophus ferrumequinum was analysed from faeces and prey remains from feeding sites through one breeding season. Light traps measured prey availability. (2) Previous studies have indicated opportunistic feeding, but rhinolophids use echolocation which may interpret insect wingbeat characteristics to select insect types (e.g. according to taxa, size). (3) R. ferrumequinum selectively dismembered large prey at perches, reducing energy costs. The diet varied over the season and consisted mainly of Lepidoptera (40.61% by volume) and Coleoptera (33.24%). Hymenoptera and Diptera were taken. More large items than expected by chance could result from the bats' acoustic search fields, or from selection. (4) More males than females of the cockchafer M. melolontha were eaten in May-June. The diet was most diverse in spring and autumn, when preferred prey items (moths) were scarce, and narrowest during late pregnancy, when moths constituted most of the diet. (5) R. ferrumequinum conforms to optimal foraging models for predators sensitive to the environment: selection for prey size, and rejection of unprofitable prey (Diptera and ichneumonids) except when more profitable prey (moths) were scarce was apparent. R. ferrumequinum certainly does not forage opportunistically.