Informing wind energy development: Land cover and topography predict occupancy for Arizona bats

Area of Science:

• Ecology
• Conservation Biology
• Renewable Energy Impacts

Background:

• Wind energy use has tripled globally in the last decade, raising concerns about bat mortality, particularly for migratory species.
• The southwestern United States, with high bat diversity and migratory routes, requires better understanding of seasonal bat distribution to assess wind energy development risks.
• Bat species of conservation concern and migratory bats face potential threats from wind energy infrastructure.

Purpose of the Study:

• To spatially and temporally characterize bat occupancy in northern Arizona, focusing on summer reproductive and fall migratory periods.
• To identify occupancy patterns of migratory bats and species of conservation need in areas with potential wind energy development.
• To develop a predictive occupancy map to identify potential conflicts between wind energy projects and bat populations.

Main Methods:

• Acoustic detectors were deployed at 92 sites across 10 clusters in northern Arizona over two years (2016-2017).
• Sampling occurred for 6 nights per site, covering both summer and fall seasons to capture different bat activity periods.
• Bat occupancy was modeled against nine landscape variables using Program MARK to predict species' responses.

Main Results:

• During summer, higher forest density correlated with increased occupancy probability for migratory bats (e.g., hoary bats, silver-haired bats) and spotted bats.
• In fall, a higher concentration of valleys, increased elevation, and proximity to forests predicted occupancy for hoary bats, big free-tailed bats, and spotted bats.
• Specific bat species, including hoary bats, silver-haired bats, big free-tailed bats, and spotted bats, showed distinct landscape preferences during different seasons.

Conclusions:

• Bat occupancy varies seasonally, with migratory species and species of conservation concern showing preferences for forested areas in summer and valleys/forest proximity in fall.
• Siting wind turbines in open, flat grasslands, away from forested landscapes and topographic variations like valleys, is recommended to reduce bat mortality.
• This research provides crucial data for informed wind energy development planning to mitigate impacts on sensitive bat populations in the southwestern United States.