Applying mobile acoustic surveys to model bat habitat use across sinuous routes

Mobile acoustic surveys allow estimates of overall bat activity, relative abundance, and species richness across large areas. Protocols for estimating relative abundance recommend using non-sinuous routes to ensure individual bats are only recorded once. We conducted mobile acoustic surveys along 12 sinuous routes in the mountainous terrain of northeastern Tennessee. Our objectives were to 1) determine if more calls were recorded in sinuous segments of mobile survey routes, thus violating assumptions of mobile surveys, and 2) analyze mobile transect data to assess bat habitat use. To test for effects of road sinuosity, we divided transects into similar to 1.6-km segments, calculated a sinuosity value, and summed the number of identified call files recorded for each segment. Using generalized linear models, we determined sinuosity did not affect the number of identified acoustic files. We assessed habitat use for 3 bat phonic groups (Low, Mid, Myotis), comparing 10 models with temporal detection and spatial occupancy covariates. Date were informative for all phonic groups. Low and mid-frequency bats were more likely to be detected on later survey dates within the summer, whereas Myotis bats had a higher probability of detection earlier within the season. As proportion of agriculture around the transect segment increased, probability of use by low-frequency bats decreased. The proportion of forest surrounding the transect segment had a positive effect on use by Myotis bats. No environmental covariates were informative regarding mid-frequency bats. We conclude that mobile acoustic surveys are an efficient method for gathering data on habitat use by bats. We recommend following guidelines set forth by the North American Bat Monitoring Program for mobile acoustic surveys but note that sinuosity of the route did not affect the number of calls recorded in our study; thus, we suggest that sinuous roads in mountainous terrain are appropriate for mobile acoustic transects.

Automated summary

Mobile acoustic surveys are effective for estimating bat activity, relative abundance, and species richness. Sinuosity of the route does not affect the recorded number of bat calls. Bat habitat use is influenced by dates and surrounding environmental factors.