Feeding behaviour and foraging strategy of free-living mouse-eared bats, Myotis myotis and Myotis blythii

This paper describes the feeding behaviour and foraging strategy of the sibling mouse-eared bat species Myotis myotis and M. blythii under natural conditions. In the Swiss Alps, the main prey of M. myotis consisted of carabid beetles (46% by volume), whereas bush crickets contributed most to M. blythii's diet (60%). However, the diet varied seasonally in both species: although they were probably a predictable food source throughout the season, carabids were under-represented in the diet of M. myotis in May and September; and when bush crickets were unavailable in May and June, they were replaced by cockchafers in M. blythii's diet. The bats selected alternative, more abundant and/or more profitable prey at certain times of the year, mostly by switching from their traditional feeding habitats to secondary (usually temporary) foraging grounds. Direct visual observations in temporary food patches showed that mouse-eared bats gleaned most prey on the soil surface while flying, but cockchafers were usually caught in flight; foraging behaviour was highly flexible. The results suggest that mouse-eared bats are opportunistic predators that maximize their average rate of food intake by balancing habitat selection. (C) 1996 The Association for the Study of Animal Behaviour