Trade-offs in habitat use and occupancy of bats across the gradient of urbanization and seasons

Urbanization, occurring across a gradient from low- to high-density
development, is a primary driver of landscape change that can affect
biodiversity. Animals balance trade-offs in obtaining resources and
avoiding anthropogenic disturbances across the gradient of urbanization to
maximize their fitness. However, additional research is necessary to
understand seasonal variations in how animals respond to urbanization,
particularly in arid regions, where resource availability shifts
drastically across seasons. Our objective was to evaluate the response of
a suite of bat species to urbanization and whether species shift their
response to urbanization across seasons. We predicted that the response of
bats to urbanization would differ among species, with some species being
more sensitive to urbanization than others. We also predicted that bat
species would increase use of moderate and highly urbanized areas in the
summer season, where food and water resources were assumed to be greater
compared to wildland areas. To evaluate these predictions, we used a
stratified random sampling design to sample 50 sites with stationary
acoustic bat monitors across the gradient of urbanization in the Phoenix
metropolitan area, Arizona, USA during four seasons. We identified a total
of 14 bat species during 1000 survey nights. Consistent with predictions,
bat species exhibited different responses to urbanization, with most
species exhibiting a negative relationship with urbanization, and some
species exhibiting a quadratic or positive relationship with urbanization.
Counter to predictions, most species did not appear to shift their
response to urbanization across seasons. Differences in the response of
bat species to urbanization was likely related to species traits (e.g.,
wing morphology and echolocation call characteristics) and behavioral
strategies that influence a species’ susceptibility to anthropogenic
disturbances and ability to access available resources in urbanized areas.
Consistent with predications, plant productivity and water were important
for some species in the summer season. Ultimately, to promote the
management and conservation of bats, it is likely important to maintain
resources in urbanized areas for bats that are more tolerant of
urbanization and to conserve areas of undeveloped high-quality habitat
with low anthropogenic disturbance in wildland areas for bats that are
sensitive to urbanization.