Comparison of Driving Transect Methods for Acoustic Monitoring of Bats

Abstract

Acoustic monitoring for bats along driving transects typically involves recording call sequences (bat passes) continuously while driving. While this offers benefits over other survey techniques, it also poses challenges, including background noise on recordings. An alternative approach that may rectify this involves conducting sampling at discrete points along each transect instead. We compared these methods using the same bat detector, along with an additional higher sensitivity detector to determine which method yields the highest amount and quality of data per unit of time. Results from 26 18 km transects, each sampled continuously and at 10 point count sites indicate that, with a lower sensitivity detector, the two methods yield a similar number of passes per min- ute, percent of passes identified to species, and species documented. The higher sensi- tivity bat detector could not be used for continuous sampling due to background noise. However, at point count sites, the higher sensitivity detector recorded 17 times more passes per minute, 44 times more passes identified to species, and documented nearly twice as many species. Thus, while both sampling designs appear comparable, for most applications, a higher sensitivity detector trumps sampling design.