Acoustic bat surveys at Tallgrass Prairie National Preserve, 2014-15

Licht, Daniel

Bats have recently become a taxon of elevated conservation concern in part because of the non-native disease white-nose syndrome (WNS). WNS was first detected in 2006 in hibernating bats in a cave in New York State and has since killed an estimated 6-7 million individuals. The disease and the causal fungus are now known to be present in several Midwestern states. As a result, the National Park Service has committed resources to better understand the status of bats in the region. Tallgrass Prairie National Preserve is a 10,894-acre park located in the tallgrass biome of east-central Kansas. Park personnel used field-deployed automated equipment to record the echolocation calls of bats in September 2014 and in July-October 2015. A total of 49,028 recordings, of which 90% had detectable bat pulses, were collected from 13 monitoring stations over 360 survey-nights. Automated software analysis of the recordings indicates that the big brown, eastern red, hoary, silver, tri-colored, and Mexican (Brazilian) free-tailed bats were present in the park, and the evening and little brown bats were likely present. I used the software to look for evidence of the endangered Indiana and gray bats and the threatened northern long-eared myotis, even though the park is outside the known range of the former two species. There was negligible evidence of the Indiana bat and the northern long-eared myotis. The latter was reported from a 2004 acoustic survey; however, the sample size was apparently small and acoustic surveys are problematic for definitive species identification. Surprisingly, the software indicated the gray bat was present. Vetting of the suspect calls by an expert was inconclusive. Mist-netting is needed for confirmation. The software assigned about ½ of the recordings to the eastern red bat suggesting it’s the most abundant species in the park. The average number of bat detections per night was 122 (using Kaleidoscope software); however, there were substantial differences between sites. The highest rate of bat activity was recorded at a large stock pond in the prairie (311 detections per night) followed by a site in the Fox Creek riparian forest and a site at the park headquarters (about 230 detections per night for each). Bat activity showed a modest peak in the 1-2 hours after sundown; however, night-time activity patterns varied by monitoring station. The stock pond mentioned above showed a dramatic peak in activity in the 1-2 hours following sundown whereas the forested Fox Creek riparian and headquarter sites had the major peak in the few hours before sunup. This could be due to the former being used for drinking and foraging whereas the latter two sites were used more for social behavior and daytime roosting. Bat activity was highest in July to mid-August with substantially fewer recordings from mid-August to early October. It’s possible the July to early August recordings included volant young that dispersed by late summer. All 10 stations monitored in September of both 2014 and 2015 showed fewer detections in 2015. The decline was statistically significant. It appeared to be driven by a decrease in the eastern red and evening bats, the most commonly detected species. Those species are not known to be vulnerable to WNS so the reason for the decline is not easily explained. The bat community at the park appears healthy, although the decline from September 2014 to 2015 is cause for concern. The surveys reported here should be replicated in future years to monitor changes over time. Old trees and surface water in the park should be conserved for the benefit of bats.

Acoustic bat surveys at Tallgrass Prairie National Preserve, 2014-15

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