Field Notes
U.S. Fish & Wildlife Service
Field Notes Entry   
Investigating the Feasibility of Enlarging an Internal Cave Passage in Beaver Dam Cave to Benefit a Maternity Colony of Gray Bats as Part of a Section 7 Consultation with FERC and USACE
Southwest Region, October 1, 2007
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  Author: Richard Stark    

Location: Beaver Dam Cave, Delaware County, Oklahoma

Participants: Richard Stark, Oklahoma Ecological Services Field Office; Steve Hensley, Ozark Plateau National Wildlife Refuge; Keith Martin, Rogers State University, and Bill Puckette

Executive Summary: Richard Stark of the Oklahoma ES Field Office; Steve Hensley, manager of the Ozark Plateau National Wildlife Refuge; Dr. Keith Martin, Rogers State University, and Bill Puckette visited Beaver Dam Cave to investigate the feasibility of increasing the size of an internal passage.  The water level in Beaver Dam Cave, which is used by a maternity colony of gray bats, is affected by water levels in Grand Lake.  The Service anticipates take of gray bats within Beaver Dam Cave near Grand Lake due to flooding associated with the lake operation that can result in inundation of the main flyway.  During an exit count effort conducted on July 19, 2007, two smaller (<1-foot wide and tall), higher elevation passages were found that potentially would allow bats to exit and re-enter the cave from their roost site while the main flyway is inundated.  However, it is highly likely that the small size of the passages currently limits their use as a flyway, especially when considering the size of the bat colony (about 12,000 bats).  A potential conservation measure currently being discussed would consist of increasing the size of the passage that occurs at the highest elevation.  A large, high elevation passage would greatly enhance the ability of bats to enter/exit the cave and would reduce the chance of take by providing a larger exit for the bats when the main flyway is inundated.  The possibility of take of non-volant young also would be reduced because the enlarged high passage would allow easier movement of adult females in and out of the cave.  The adult females, therefore, could continue to take care of their non-volant young should the main flyway become inundated during the early summer.  Based on our investigation and initial limited excavation work, it appears that the highest elevation passage could be enlarged substantially.  We believe it could be enlarged enough to allow an average-sized adult human to easily move through the passage.  The Service anticipates working with the Corps and GRDA to 1) obtain baseline temperature and humidity data of the cave during the winter and summer seasons prior to enlarging the passage, 2) enlarge the highest elevation passage during the fall/winter when bats are not present, 3) subsequently monitor the effect of the passage modification on the temperature and humidity of the cave, and 4) conduct exit counts during the maternity season following passage modification to determine if the gray bat colony accepts the modification. 

FWS programs involved: Ecological Services and Refuges

External partners involved: U. S. Army Corps of Engineers, Federal Energy Regulatory Commission, the Grand River Dam Authority, and Rogers State University

Contact Info: Martin Valdez, 505-248-6599, martin_valdez@fws.gov
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