Ozark big-eared bat monitoring at Ozark Plateau National Wildlife Refuge

OBEB from video

Population counts of Ozark big-eared bat (Corynorhinus townsendii ingens) maternity colonies have been performed annually for several decades. The process consists of lighting the cave entrance with infrared lights and using night vision goggles to determine how many Ozark big-eared bats fly out. Bats are extremely good fliers and can exit out of the cave very fast. It takes several years to develop the skills to be an accurate counter. In the summer of 2006, Richard Stark of the Oklahoma Ecological Services Field Office began utilizing infrared video and acoustic detectors to supplement the traditional count method. The infrared video and acoustic method consisted of deploying a single Anabat near the cave entrance and filming the bat emergence with the use of a Sony Handycam with nightshot and infrared lights. The video footage was then later reviewed in slow motion on a large television screen to obtain a count of Ozark big-eared bats exiting the cave. Ozark big-eared bats could be distinguished from other species by their large ears which are over 1 inch long. When a bat suspected to be an zark big-eared bat on film could not be confirmed by the video footage alone, the Anabat data were reviewed to determine if a bat call was recorded at the same time the suspect bat emerged from the cave for possible confirmation. The method proved successful and showed great promise. Colony size estimates from the infrared video method were compared to estimates by the traditional count method, and results were very similar. The infrared video and acoustic method also detected use of two caves in Cherokee County, Oklahoma by Ozark big-eared bats that was not detected by the traditional method conducted simultaneously. These caves subsequently have been added to the annual monitoring efforts and are now known to be used by a colony of Ozark big-eared bats at various times of the year. Although the new infrared video and acoustic detector method proved very valuable, due to time and resource limitations, the method was utilized at only a few caves per year between 2006 and 2008.

The initial success of the method warranted expanded use and fine-tuning of the technique. Ozark Plateau National Wildlife Refuge in conjunction with the Service’s Inventory and Monitoring Program expanded use of the method in 2009. The method currently being utilized consists of filming the bat emergence with two or more cameras from multiple angles and deploying multiple acoustic detectors (both Anabat and Pettersson units). A black backdrop also is now utilized which enhances the counter’s ability to identify Ozark big-eared bats. The number of caves at which this technique is utilized also has been expanded to about 25 per summer and includes the essential maternity caves and numerous limited-use sites.

Video monitoring has several advantage over the traditional method. First, it doesn’t take several years to become an accurate counter. Second, video playback allows counter to slow down playback and use individual frames to identify Ozark big-eared bats. The video is time stamped to provide a log of the time of each bat’s emergence. Since the video has a time stamp and the acoustic monitors can be time synced, we can get a total bat species population count for each cave. With the threat of white nose syndrome it is important that we get population data on all cave dwelling bat species. White nose syndrome is non selective and can affect all cave dwelling species.

Click here for a short video on Ozark big-eared bat monitoring at Ozark Plateau National Wildlife Refuge


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