Going beyond a leap of faith when choosing between active and passive bat monitoring methods

摘要

The limiting trade-off between expediency and accuracy is well exemplified by the monitoring of bats, more specifically since the onset of the White-Nose Syndrome in North America. Acoustic detection is a way of circumventing the difficulties of catching bats, and monitoring is usually done either with transects or fixed recording points, the latter generally being assumed to be superior. However, little has been done until now to assess each method's ability to maximize the quality of recordings and the number of species detected, to account for the temporal variability of bat activity, and to account for the variability in habitats and the spatial patterns of bat activity. We tested whether transects could yield similar results as fixed points for every of those aspects of accurate and reliable bat monitoring. We found it to be true for recording quality and the detection of peaks of activity, but found that either method was little affected by weather and landscape attributes. We conclude that the use of transects is a valid choice for long-term monitoring, as it performs comparably to fixed recording points and maximizes the number of detections per sampling unit. However, transects tend to record a greater proportion of migratory bats than fixed recording points, a bias which should be considered in the assessment of the state of particular species' populations.