Bats are Not Birds--a Cautionary Note on Using Echolocation Calls to Identify Bats: a Comment

Monitoring and identifying echolocating bats in the field has been used extensively for many years, and O'Farrell et al. (1999) present an updated "qualitative" method for identifying species from their echolocation calls. However, they make the assumption that, like bird songs, echolocation calls of bats are species-specific. There is no reason to expect that natural selection favored incorporation of this information. Although identification of some species of bats by their calls is possible, variation at several levels makes other species indistinguishable. Monitoring echolocation in the field and identifying species can be useful in determining presence or absence of species and factors influencing activity of bats. However, limitations and degree of reliability of the technique must be recognized. Only by more explicitly defining how the method is used and quantifying characteristics that define calls of recognizable species will the method be scientifically sound and repeatable. I suggest a number of guidelines for use of the method in field studies.