New study models decline in hoary bats using NABat monitoring data
A collaborative research effort based at Oregon State University – Cascades has concluded that summer hoary bat populations in the Pacific Northwest are in decline. In a paper just published in Ecology and Evolution, researchers examined occupancy trends in Oregon and Washington by comparing data collected from 2003-2010 with new data collected in collaboration with NABat from 2016-2018. In addition to documenting a decline in regional hoary bat populations, the study demonstrates the continent-wide monitoring program's potential to reveal emerging threats to North American bat species. By aggregating data from regional partners across North America, future NABat analyses will help identify the drivers of population change and inform recovery efforts for threatened species.
There is growing concern among researchers about the impact of wind energy production on hoary bats, which commonly collide with the spinning blades of turbines. Although the exact number is uncertain, most estimates place annual bat fatalities in the tens to hundreds of thousands. In the U.S., the majority of bat fatalities occur in migratory species, and hoary bats are the most heavily impacted.
Researchers also examined occupancy rates of the little brown bat, but found no evidence of regional declines. The widely distributed species has undergone significant declines in eastern states and parts of Canada, where the fungal disease white-nose syndrome is blamed for more than 6 million bat fatalities since its discovery in New York in 2006. The disease, which has since spread to 33 states and seven Canadian provinces, was first confirmed in the Pacific Northwest in 2016, and researchers were interested in whether it has begun to impact western populations. The little brown bat is currently listed as a threatened species in Canada and has been considered for federal protection in the U.S.
More broadly, the paper stresses the potential to update previous monitoring efforts with new data using Bayesian inference. This approach incorporates historic data into prior distributions that inform new modeling efforts, allowing researchers to combine monitoring efforts that often have years-long gaps in data collection. To test the approach, authors compared models that utilized historic data to models with no prior data. While overall trends were not influenced, incorporating prior data produced more precise estimates of occupancy and strengthened evidence of declines in hoary bat populations.
The collaborative study was funded by the Oregon Department of Fish and Wildlife, National Park Service, U.S. Fish and Wildlife Service, U.S. Forest Service, Bureau of Land Management, and U.S. Geological Survey.
Read the full paper here.