Insectivorous Bat Occupancy Is Mediated By Drought And Agricultural Land Use In A Highly Modified Ecoregion

Aim California's Central Valley, one of the most productive agricultural regions worldwide, is home to a high number of at-risk species due to habitat conversion. Amplifying the issue, the Central Valley faces severe droughts, creating water scarcity in surrounding natural areas. At least 14 insectivorous bat species live in this region, and prior studies show mixed results regarding the impact of agriculture and drought on bats. The aim of this study was to investigate how bats use agricultural areas during drought.Location Central Valley, California, United States.Methods We deployed ultrasonic acoustic detectors at 274 sites from March through July of 2016, the final year of an extreme drought, and 2017, one of the wettest years on record. We identified bats to species, used single-species occupancy models including biologically relevant covariates and created spatial projections of ecoregion-wide occupancy for each species.Results We modelled occupancy for eight bat species. Long-distance migrants in the study area contracted their geographic range during the drought, while resident species did not. Five of the eight bats in this analysis were more likely to occupy areas with orchard crop cover. Lastly, arid-adapted bats used cultivated landscapes during the drought but retracted their range after the drought ended.Main conclusions Migratory bats appeared to shift occupancy more during drought than resident bats, possibly because of lower roost fidelity. Additionally, the effects of drought on some bat species in the Central Valley may be buffered by agricultural landscapes acting as drought refugia. Overall, this study demonstrates the benefits of broad-scale acoustic studies which can serve as a tool to track changing bat distributions on the landscape and provide baseline occupancy for acoustically detectable species.