Bat habitat use along a gradient of urbanization varies seasonally in relation to forage and water availability

Background/Question/Methods

Anthropogenic factors can create novel environments for animals, where each species responds differently to landscape modifications in order to balance trade-offs to maximize their fitness. In particular, urbanization, occurring across a gradient from low- to high-density development, is a pervasive and expanding driver of landscape change that can affect biodiversity, where some species benefit, and others are negatively impacted. Bats play important roles in ecosystems around the world and can be sensitive to urbanization. In addition to urban intensity, bat habitat use is influenced by forage and water availability. Areas with increased plant productivity and water are assumed to have increased forage resources for bats. However, it is unclear how these trade-offs potentially change temporally in environments with dramatic shifts in resource availability across seasons. Our objective was to evaluate seasonal variation in bat habitat use across a gradient of urbanization in an arid region. To achieve this, we deployed acoustic bat monitors at 50 sites across the Phoenix metropolitan area with varying levels of urbanization and surveyed the sites during each of the four seasons of 2019. We expected bat habitat use to vary seasonally in relation to urban intensity, plant productivity and distance to water.

Results/Conclusions

We detected 14 bat species over the course of the study, 9 of which had sufficient data in two or more seasons. We recorded the most bat detections in the summer and least bat detections in the winter. As expected, bat species varied in their response to urbanization. Some bats, such as the canyon bat (Parastrellus hesperus) were more associated with wildland areas, whereas other bats, such as the Mexican free-tailed bat (Tadarida brasiliensis), remained urban associated year-round. Other bats had a quadratic relationship with urbanization, such as the Yuma myotis (Myotis yumanensis), which peaked in relative abundance at moderate levels of urbanization in the spring and summer season. In addition to urban intensity, bat species exhibited varying relationships with plant productivity and water across seasons. For example, T. brasiliensis selected for areas with higher plant productivity and more water in the spring and summer seasons, whereas P. hesperus selected for areas with higher plant productivity in the winter season. Overall, our results suggest that bat habitat use along a gradient of urbanization varies seasonally, which is potentially related to increased plant productivity and water in urban areas compared to wildland areas in some seasons.