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A new activity index for acoustical bat data is presented. The AI (acoustic activity index) was highly correlated to bat passes but proved to be a less biased index of activity. The method dispenses with the need to define, identify and count bat passes and provides a simple means to quantify activity. It uses the Anabat system where acoustic surveys are carried out in real time with the data saved directly to a computer hard drive, taking advantage of the date-time information encoded into each file. The method is based upon the presence/absence of a species occurrence during one-minute time intervals and avoids skewing an index of activity that may reflect the behavior of the species sampled. Examples are given showing that the AI is an effective measure of bat activity allowing comparisons between sites, times and species.
We present the results of an acoustic survey of aerial insectivorous bats conducted in four protected areas in northern Venezuela. These areas represent localities where the taxonomic composition of the bat communities was relatively well known. We conducted field surveys using the Anabat II detector and analysis system. We compared acoustic inventories with previous lists obtained with conventional sampling methods (principally mist nets). We identified 30 species acoustically (representing 15 genera of the families Emballonuridae, Noctilionidae, Mormoopidae, Vespertilionidae, and Molossidae) on the basis of vocal signatures. Nineteen of these were verified by capture and subsequent recording of released animals; the remainder were identified by comparison with verified vocalizations from other localities. An additional 11 unidentified but distinct taxa were recorded and are referred to here as ‘sonotypes’ (based on similarities in call structure to known species) representing eight genera of the families Emballonuridae, Vespertilionidae, and Molossidae. The short-term acoustic surveys nearly equaled or exceeded the known species richness at three of the four localities, and added two to nine species to previous lists from all locations; many of these bats correspond to taxa difficult to detect with conventional capture methods.
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