Document Title:

Contaminants in Bats Roosting in Abandoned Mines at Imperial National Wildlife Refuge, Arizona, 1998-1999

Anthony L. Velasco Kirke A. King Jackie A. Record Ronald L. Kearns

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This report documents levels and potential effects of trace element and organochlorine pesticide concentrations in four bats species collected from four abandoned mines on Imperial National Wildlife Refuge (NWR) and from three southern Arizona reference sites. With the exception of arsenic in the big brown bat (Eptesicus fuscus) and copper in California myotis (M. californicus) and Yuma myotis (M. yumanensis), there appears to be little potential for heavy metal related adverse effects in bats. Lead concentrations in Yuma myotis collected from the Eureka Mine were 5- to 10-times higher than concentrations in samples from the reference site; however, it is not known what concentrations of lead are associated with sublethal effects such as impaired learning and behavior. Bats collected from an abandoned mine in the intensively cultivated lower Gila River valley, approximately 137 km east of Imperial NWR, contained significantly higher organochlorine concentrations, including residues of DDT, than those from other sites; but, maximum concentrations were below adverse effect thresholds. The population of Yuma myotis roosting at Imperial NWR’s Eureka Mine, a mine complex with multiple entrances, appeared to consist of several sub-populations based on chemical profiles of bats collected at different entrances. Samples collected from three entrances exhibited significant differences in whole body burdens of aluminum, cadmium, chromium, copper, iron, manganese, selenium, and zinc. These unique entrance-specific contaminant profiles suggested that: 1) individuals from each entrance either fed in separate Colorado River habitats, and/or 2) bats from each entrance wintered in distinct environments, and/or 3) contaminant profiles were modified at the roost site by ingestion or inhalation of dust containing different ratios of various elements. At Sheep Tank Mine, a reference site at Kofa NWR, barium, manganese, and zinc were detected in soil at concentrations at least 10-times higher than previously reported in Arizona. Big brown bats from the same mine also contained significantly higher concentrations of these elements than big brown bats collected from three other sites. Metals acquired at the roost site may be at least as important as those bioaccumulated through the food chain. Further studies are scheduled to test the hypothesis that body burdens in bats may, in part, be a reflection of ingestion of metals through the grooming process, and/or through inhalation of metal-laden dust particles at the roost site. DEC ID No. 199820002

U.S. Fish and Wildlife Service


Last updated: June 12, 2015