Monitoring and Modeling Tree Bat (Genera: Lasiurus, Lasionycteris) Occurrence Using Acoustics on Structures off the Mid-Atlantic Coast—Implications for Offshore Wind Development

Abstract

In eastern North America, “tree bats” (Genera: Lasiurus and Lasionycteris) are highly susceptible to collisions with wind energy turbines and are known to fly offshore during migration. This raises concern about ongoing expansion of offshore wind-energy development off the Atlantic Coast. Season, atmospheric conditions, and site-level characteristics such as local habitat (e.g., forest coverage) have been shown to influence wind turbine collision rates by bats onshore, and therefore may be related to risk offshore. Therefore, to assess the factors affecting coastal presence of bats, we continuously gathered tree bat occurrence data using stationary acoustic recorders on five structures (four lighthouses on barrier islands and one light tower offshore) off the coast of Virginia, USA, across all seasons, 2012–2019. We used generalized additive models to describe tree bat occurrence on a nightly basis. We found that sites either indicated maternity or migratory seasonal occurrence patterns associated with local roosting resources, i.e., presence of trees. Across all sites, nightly occurrence was negatively related to wind speed and positively related to temperature and visibility. Using predictive performance metrics, we concluded that our model was highly predictive for the Virginia coast. Our findings were consistent with other studies—tree bat occurrence probability and presumed mortality risk to offshore wind-energy collisions is highest on low wind speed nights, high temperature and visibility nights, and during spring and fall. The high predictive model performance we observed provides a basis for which managers, using a similar monitoring and modeling regime, could develop an effective curtailment-based mitigation strategy.

Mid-Atlantic Big Brown and Eastern Red Bats: Relationships between Acoustic Activity and Reproductive Phenology

“…This result is similar to Muthersbaugh et al [ 46 ], where Julian day did not predict eastern red bat acoustic activity from September through mid-November, perhaps because bats had largely ceased migration by that period. Our call asymptote and late-summer declines are similar to those patterns observed in eastern red bats in areas with viable roosting habitats along the nearby Delmarva Peninsula [ 47 ]. Further analysis to determine large-scale patterns and habitat use of eastern red and big brown bats during these migration periods is needed.…”

Biotic and abiotic factors shaping bat activity in Maryland soybean fields

“…The wind speeds experienced in our study area, located on the western shore of the Chesapeake Bay, may have differed in directionality and force compared with sites on the Atlantic Ocean proper. Indeed, the highest average hourly wind speed was 5.8 m/s (~21 km/h), which is approximately half the average hourly wind speed reported by True, Reynolds, et al (2021) on the eastern shore of the Chesapeake Bay. Furthermore, our analysis also did not account for wind direction nor wind profit (a combination of wind speed and direction; Erni et al, 2002).…”

“…In the most recent acoustic and mist‐netting bat surveys of eastern Maryland and adjacent Virginia, 10 individual bat species were detected (Deeley et al, 2021; Neece, 2019; True, Perry, et al, 2021; True, Reynolds, et al, 2021), all of which are listed as vertebrate species of greatest conservation need (Maryland Department of Natural Resources, 2015). The big brown ( E. fuscus )/silver‐haired ( Lasionycteris noctivagans ) bat species group, two species commonly combined due to high uncertainty in acoustic auto‐identification software (Ford, 2014), was the most abundant group in these surveys, followed by eastern red bats ( Lasiurus borealis ; Neece, 2019).…”

“…For example, if HIPV‐based lures could be developed to attract insectivorous bats to agricultural fields, it could be beneficial to deploy these during optimal weather conditions to enhance bat biocontrol services and thus increase profitable yield. In the southeastern United States, nightly bat activity is generally positively correlated with temperature and negatively correlated with rain and wind speed (Bender & Hartman, 2015; Ford et al, 2006; Johnson et al, 2011; Muthersbaugh et al, 2019; Sjollema et al, 2014; True, Reynolds, et al, 2021). Windy or rainy conditions increase thermoregulatory and flight energy costs and decrease insect activity.…”

“…In addition to biotic factors, abiotic factors, including temperature, precipitation, wind speed, and atmospheric pressure, can strongly influence bat activity (Gorman et al, 2021). Predicting fine‐scale bat activity at the hourly timescale can help inform best land management practices (in agriculture, but also forestry and wind energy development; True, Reynolds, et al, 2021). For example, if HIPV‐based lures could be developed to attract insectivorous bats to agricultural fields, it could be beneficial to deploy these during optimal weather conditions to enhance bat biocontrol services and thus increase profitable yield.…”