Comparison of sampling methods for inventory of bat communities

From 1999 to 2005, we sampled the bat fauna of Catalonia (northeastern Spain, Mediterranean region) using 3 methods (bat detectors, mist nets, and roost surveys) and determined the total number of bat species present (S = 22). Twelve bat species and 5 acoustic groups (>= 5 different species) were identified using bat detectors, 17 species were found during roost inspections, and 13 species were trapped using mist nets. However, mist nets yielded the highest species richness per number of individuals sampled, as demonstrated by rarefaction. Some species were always either over- or undersampled according to the sampling method used. We also evaluated 3 guilds of bats defined by summer roost preferences, documenting a significant correlation between guild and detection method; cavity-roosting bats were underrepresented when only bat detectors and mist-net surveys were used, whereas rock crevices or man-made structure and tree guilds were underrepresented when only roosts were surveyed. Different techniques should be used to assess the richness of bat communities and we recommend combining all the methods described above in future bat surveys.