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

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. ? 1996 The Association for the Study of Animal Behaviour Recent studies on the diet and foraging behaviour of insectivorous bats have confirmed Norberg & Rayner’s (1987) predictions based on wing morphology that a large proportion of species are able to catch prey from surfaces (Bauerova 1978, 1986; Fenton & Bell 1979; Bell 1982; Swift & Racey 1983; Jones & Rayner 1988; Rydell 1989; Barclay 1991; Beck 1991, 1994–1995; Kalko 1991; Krull et al. 1991; Shiel et al. 1991; Faure & Barclay 1992; Taake 1992; Wolz 1993). For instance, among the 25 species presently occurring in Switzerland, at least nine (36%) are considered to be gleaning bats, all of them belonging to the genera Myotis and Plecotus (Beck 1994–1995). Microchiroptera have been reported to glean prey from all types of surfaces: water, ground, grass, cliff walls, tree bark, branches or leaves (Fenton 1982). However, gleaning bats may also switch from gleaning to aerial-hawking foraging strategies (Anderson & Racey 1991; Barclay 1991; Krull et al. 1991; Faure & Barclay 1992; Krull 1992). In Central Europe, the greater mouse-eared bat, Myotis myotis, preys mainly on flightless carabid beetles (Carabidae; Kolb 1958; Bauerova 1978; Gebhard & Hirschi 1985), and is thus believed to be an exclusive ground-gleaning predator (e.g. Rudolph 1989; Audet 1990). Radio-tracking studies carried out on M. myotis in Germany (Liegl & Helversen 1987; Rudolph 1989; Audet 1990) have failed to provide a detailed description of its foraging behaviour under natural conditions (Krull et al. 1991); as this species was foraging exclusively in woodland (Rudolph 1989; Audet 1990), the vegetation probably precluded any direct visual observations. The ecology of the lesser mouse-eared bat, M. blythii, is poorly documented, owing both to its southern distribution (most ecological studies on European bats have concerned species of the northern latitudes) and to the difficulty of distinguishing it from M. myotis (Ruedi et al. 1990; Arlettaz et al. 1991). Preliminary dietary studies showed that M. blythii feeds mainly on bush crickets (Tettigoniidae) gleaned from grass Correspondence: R. Arlettaz, Institute of Zoology and Animal Ecology, Biology Building, University of Lausanne, CH-1015 Lausanne, Switzerland (email: raphael.arlettaz@izea.unil.ch). 0003–3472/96/010001+11 $12.00/0 ? 1996 The Association for the Study of Animal Behaviour