Evidence of region‐wide bat population decline from long‐term monitoring and Bayesian occupancy models with empirically informed priors

Abstract

Strategic conservation efforts for cryptic species, especially bats, are hindered by limited understanding of distribution and population trends. Integrating long‐term encounter surveys with multi‐season occupancy models provides a solution whereby inferences about changing occupancy probabilities and latent changes in abundance can be supported. When harnessed to a Bayesian inferential paradigm, this modeling framework offers flexibility for conservation programs that need to update prior model‐based understanding about at‐risk species with new data. This scenario is exemplified by a bat monitoring program in the Pacific Northwestern United States in which results from 8 years of surveys from 2003 to 2010 require updating with new data from 2016 to 2018. The new data were collected after the arrival of bat white‐nose syndrome and expansion of wind power generation, stressors expected to cause population declines in at least two vulnerable species, little brown bat (Myotis lucifugus) and the hoary bat (Lasiurus cinereus). We used multi‐season occupancy models with empirically informed prior distributions drawn from previous occupancy results (2003–2010) to assess evidence of contemporary decline in these two species. Empirically informed priors provided the bridge across the two monitoring periods and increased precision of parameter posterior distributions, but did not alter inferences relative to use of vague priors. We found evidence of region‐wide summertime decline for the hoary bat (trueλ^ = 0.86 ± 0.10) since 2010, but no evidence of decline for the little brown bat (trueλ^ = 1.1 ± 0.10). White‐nose syndrome was documented in the region in 2016 and may not yet have caused regional impact to the little brown bat. However, our discovery of hoary bat decline is consistent with the hypothesis that the longer duration and greater geographic extent of the wind energy stressor (collision and barotrauma) have impacted the species. These hypotheses can be evaluated and updated over time within our framework of pre–post impact monitoring and modeling. Our approach provides the foundation for a strategic evidence‐based conservation system and contributes to a growing preponderance of evidence from multiple lines of inquiry that bat species are declining.

Dogs Detect Larger Wind Energy Effects on Bats and Birds

“…The nationwide estimates cited above were based on using human searchers at wind turbines, an approach prone to large biases and sources of uncertainty due to variation in fatality monitoring methods and poor detection of bat carcasses (Smallwood 2007; Smallwood et al 2010, 2013). Given the potential magnitude of wind turbine effects on bats and their possible contribution to regional population declines (Rodhouse et al 2019), it is important to improve estimates of bat fatality rates to formulate realistic mitigation measures.…”

Peer Review #1 of "Using trace elements to identify the geographic origin of migratory bats (v0.1)"

“…Other results (e.g. Rodhouse et al 2019) support this prediction, highlighting the threat that the expansion in renewable wind energy represents to bats (Kunz et al, 2007a). The majority of the bats killed at wind farms in North America are from three migratory species (eastern red bat; Lasiurus borealis, hoary bat; L. cinereus, and silver-haired bat; Lasionycteris noctivagans; Kunz et al, 2007a).…”

Bat Activity Rates do not Predict Bat Fatality Rates at Wind Energy Facilities

“…For example, bat activity surveys can be used to identify and provide relative activity rates of species that are protected (e.g., Indiana bat Myotis sodalis -USFWS, 2019) or might be otherwise adversely affected by wind energy at a particular facility. On a broader scale, echolocation data could be used to monitor the activity patterns of individual species at landscapelevel scales to help track the long-term viability of bat populations (Rodhouse et al, 2019) and movements across continents.…”