Case study – The Bats in Churches Project Species Pipistrelle Long-eared Serotine Natterer’s Lesser horseshoe Greater horseshoe Daubenton’s Unknown species Churches occupied by bats 63 44 7 4 3 1 2 24 Chapels occupied by bats 16 12 3 1 0 0 0 12 Proportion of roosts occupied by species (%) 50.6 35.9 6.4 3.2 1.9 0.6 Source The Bats In Churches Project, Sargent (1995).
CHAPTER 3 SURVEY AND MONITORING 32 3.4.2 Evening/dawn bat detector back-tracking A technique of locating roosts using bat detectors has been developed in the Netherlands and a full description of the method can be found in Kapteyn (1993). The technique is based on four principles: 1 The earlier a bat is seen at sunset or the later it is seen at sunrise, then the closer it is likely to be to its roost (the exact time depends on the species under study). 2 Bats flyaway from their roost at sunset and surveyors should move towards flying bats to locate the roost. 3 At sunrise bats fly towards their roost and surveyors should move in the same direction as the bats to locate the roost. 4 At sunrise some bat species swarm at roost entrances before entering for between 10 and 90 minutes. Surveyors should look for swarming bats at sunrise. Surveyors search for bats at emergence time, noting down the time bats were encountered and the direction and style of their flight, e.g. west, commuting. This information is pooled on a map to identify potential commuting routes and possible roost sites. Close to dawn surveyors search again, this time for returning bats. Potential routes identified earlier at emergence time are surveyed for bats swarming at roost entrances. Although the technique is biased towards early emerging species with loud echolocation calls and which form large roosts, it is possible to locate roosts of any species using this method.