Acoustic identification of bats from directly sampled and time expanded recordings of vocalizations

We review how time-expanded recordings and direct sampling of sound can be used to identify some bat species from their vocalizations, and how such me thods may be applied to field surveys of bat activity. Some species emit di stinctive social calls that permit identification, and social calls may be individually distinctive within species. Analysis of echolocation calls can identify cryptic species that are very similar in appearance, but differ i n echolocation calls. Echolocation calls vary according to ecology and morp hology both across and within species. Although some species emit distincti ve echolocation calls, great care must be used in the acoustic identificati on of other species, especially in cluttered habitats. Species identificati on from echolocation calls is best approached by quantitative analysis, suc h as discriminant function analysis (DFA) based on several measurements tak en from calls. DFA gives an objective measure of confidence in species iden tification, and can be applied to surveys of habitat use providing that cer tain limitations are recognised. Discrimination of species from their echol ocation calls may be improved by quantifying the shape of calls from their frequency-time course, and by using artificial neural networks. Feeding rat es can be estimated in bat detector surveys. though not all terminal buzzes emitted prior to prey capture are associated with successful capture of pr ey. Time expansion and direct sampling methods retain more detail of indivi dual echolocation calls than do other methods. Not only can these methods b e used to a certain extent for species identification and habitat use studi es, they remain the only suitable methods for describing call design in bat s from a detailed bioacoustics perspective.