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Investigations of anticoagulant rodenticide exposure in wildlife in a national park in southern California: distribution, extent, and effects of exposure in multiple carnivores, surveys of human use, and exposure in small mammals and lagomorphs
Citation:
Riley, S. D., R. H. Poppenga, J. E. Foley, A. T. MORZILLO, AND R. M. Sauvajot. Investigations of anticoagulant rodenticide exposure in wildlife in a national park in southern California: distribution, extent, and effects of exposure in multiple carnivores, surveys of human use, and exposure in small mammals and lagomorphs. Presented at 4th Pan Pacific Conference on Pesticide Science, Honolulu, HI, June 01 - 05, 2008.
Impact/Purpose:
Since 1996, we have been studying the ecology and conservation of mammalian carnivores, including bobcats, coyotes, and more recently mountain lions, at Santa Monica Mountains National Recreation Area north of Los Angeles.
Description:
Since 1996, we have been studying the ecology and conservation of mammalian carnivores, including bobcats, coyotes, and more recently mountain lions, at Santa Monica Mountains National Recreation Area north of Los Angeles. Although it was not a goal of the study, from the beginning we detected exposure to, and impacts from, anticoagulant rodenticides in native carnivores. Nine radio-collared coyotes died from anticoagulant toxicosis in the first 5 years of the study, and this was the single largest cause of mortality. We found very little direct mortality from anticoagulants in bobcats, however, beginning in 2002, an epizootic of notoedric mange, a disease previously reported only as isolated cases in wild felids, reduced the annual survival rate of bobcats from a 5-year average of 0.77 to 0.28 in two years. Anticoagulants were present in 35 of 39 (90%) bobcats tested, multiple compounds were present in 27 of these 35 (77%), and total toxicant load was positively associated with the use of developed areas by radio-collared animals. Mange-associated mortality in bobcats showed a strong association with anticoagulant exposure, as 19 of 19 (100%) bobcats that died with severe mange were exposed to anticoagulants, and for bobcats with toxicant residues > 0.05 ppm, the association with mange was highly significant (χ2=10.36, p=0.001). We speculate that rodenticide exposure may have increased the susceptibility of bobcats to advanced mange disease. Since 2004, all 9 bobcats tested have been exposed to anticoagulants, including the largest residue detected to date (2.39 ppm), and both radio-collared and uncollared bobcats have continued to develop severe mange infestations. In 2004, two adult mountain lions died directly from anticoagulant toxicity, and both animals also had infestations of notoedric mange. Of six mountain lions that have since died from other causes, five also exhibited exposure to 2-4 different anticoagulants. Broader testing of mountain lions across the state of California has revealed extensive exposure (2/3 of animals tested) in both urban and rural areas. We are also working with the EPA to survey local residents, businesses, and homeowner’s associations about their use of rodenticides and their knowledge of the potential environmental effects. Preliminary results indicate that > 50% of respondents are practicing rodent control, targeting a wide variety of species. Finally, we are beginning studies of exposure in the prey species of carnivores in different parts of the fragmented urban landscape around the park. This work also involves the potential development of a new ante-mortem test for anticoagulant exposure in wildlife. Overall, our results show that the effects of secondary poisoning on predators can be widespread, can reach the highest-level carnivores, and can have both direct and possibly indirect effects on mortality.