Acoustic interference between echolocation calls of two species of California bat (Myotis, Vespertilionidae)

Many species of bats rely on echolocation—a biological sonar system—to carry out essential survival tasks such as hunting and orienting in their nighttime environments. How bats echolocate so successfully despite considerable physical and acoustic obstacles is a fascinating problem in signal processing. Because bats often live in large groups, they encounter substantial acoustic interference from echolocating conspecifics that may impede their own ability to echolocate.

In the present study, I examine the theoretical effect of interference from conspecifics and congenerics on the target detection ability of two cohabiting species of vespertilionid bat found in California (Myotis californicus and M. yumanensis). I use the wideband ambiguity function, a tool for analyzing human-made radar and sonar systems, to assess whether it is theoretically possible for a bat to shift its call in frequency to reduce the effect of conspecific interference. I apply the same methods to investigate the effect of interfering calls from M. californicus on the target detection ability of M. yumanensis and vice versa.

Results indicate that these two species experience considerable interference from both within- and between-species calls. Incorporating data from the field suggest that a bat’s calls are shaped such that most interference an individual is likely to encounter manifests as a reduction in the bat’s ability to accurately locate a target rather than as an increase in likelihood that the bat will mistake one object for another—an adaptation that may prevent the bat from becoming disoriented or losing track of an acquired target. Differences in calls between M. californicus and M. yumanensis may reflect adaptations to environmental clutter. Further research should focus on the implications of congeneric interference for the spatial and temporal distribution of these species.