Habitat selection by barbastelle bats (Barbastella barbastellus) in the Swiss Alps (Valais)

Abstract

Recent faecal analyses have shown that barbastelle bats Barbastella barbastellus are highly specialized moth predators. The predominance of moths (> 99% by volume) in their diet both in wooded areas of the Swiss Alps and in denuded steppe areas of Central Asia further suggests that this narrow diet does not stem from a highly specialized habitat selection, but merely from peculiar species-specific foraging constraints. Non-opportunistic predators relying on a few prey types must find areas providing their basic prey in abundance. Using radiotracking, habitat selection was investigated in a population of barbastelle bats inhabiting xeric forests in the Swiss Alps. In particular, I tested the prediction that the biologically most productive areas within the forest are exploited in priority. Eleven individuals were radiotracked from June through to October 1992, and in June 1993. The home range (59 ha) of the overall radiotracked population was divided in 236 cell units of 0.25 ha each. Within each cell, habitat and vegetation structure was described using 19 environmental variables. Habitat selection by the bats was investigated through stepwise regression analysis, which retained 11 variables showing a significant positive relationship with habitat use. The four variables accounting for 31% of the overall variance were: litter thickness, percentage of shrub layer cover, percentage of pine tree cover, and circumference of oak trunks. The results showed a clear preference by barbastelles bats for richly structured forests, and an avoidance of open woodland on stony outcrops and rocky slopes. This confirms that the biologically most productive parts of the forest were exploited in priority.