Winter activity of a population of greater horseshoe bats (Rhinolophus ferrumequinum)

Activity patterns of greater horseshoe bats Rhinolophus ferrumequinum were investigated at caves in Cheddar (south-west England) during the hibernatio n season. An ultrasound detector and datalogger were used to monitor and re cord the number of echolocation calls in a single cave. Activity of R. ferr umequinum remained largely nocturnal throughout winter, and the mean time o f activity over 24 h was 88 to 369 min after sunset. There was an increase in diurnal activity from late May to early June, probably because bats rema ined active after foraging at dawn towards the end of the hibernation seaso n. Visits to the cave did not increase bat activity. Cave air temperature r eflected external climatic temperature, although there was variation in cav e temperature and its range within and among caves. Individual R. ferrumequ inum are usually dispersed in caves in regions where temperature fluctuatio ns correlate with climatic variations in temperature. There was a positive correlation between the number of daily bat passes monitored by the bat det ector and datalogger (= daily activity) and cave temperature. Nocturnal act ivity may be sometimes associated with winter feeding. Neither date nor bar ometric pressure had a significant effect on daily activity. Activity patte rns largely reflected the findings from individual R. ferrumequinum studied by telemetry (Park, 1998), in that bat activity increased with cave and cl imatic temperatures, and the temporal pattern of activity remained consiste ntly nocturnal throughout winter, starting at dusk.