The changes in echolocation behaviour and the structure of calls ofPipistrellus pygmaeus (Leach, 1825) were studied in different habitats of a floodplain forest in south-eastern Moravia (Czech Republic) in 2001–2002. Calls (403 observations) were recorded in different sites between April and mid June (before weaning) using a time expansion bat-detector. Three signals per individual were analysed and descriptive statistics of variables of calls were presented. Association of signal types with habitat structure (cluttered, side-cluttered, semi-cluttered and uncluttered space) was found in echolocation sequences of the search phase of flight.P. pygmaeus used mainly narrowband signals (bandwidths less than 15 kHz) in uncluttered space and wideband signals (more than 15 kHz) in cluttered space. Almost 6% of the inter pulse intervals of signals were twice (or more) longer than usual inter pulse intervals (mainly in uncluttered space). In general, temporal variables of signals reached higher values in uncluttered spaces (except for inter pulse interval) than in cluttered ones. On the contrary, spectral variables of signals reached lower values in uncluttered habitats in comparison with cluttered ones. In addition, the signals were less variable in open spaces while in cluttered and partly-cluttered habitats different and higher variability was found. We also studied the accuracy of identification of pipistrelles by call parameters and possible misidentifications in relation to habitat structure. Multivariate discriminant analyses were carried out on the time and frequency parameters of calls produced by pipistrelles.
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