Anticoagulant rodenticides on our public and community lands: spatial distribution of exposure and poisoning of a rare forest carnivore

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Anticoagulant rodenticide (AR) poisoning has emerged as a significant concern for conservation and management of nontarget wildlife. The purpose for these toxicants is to suppress pest populations in agricultural or urban settings. The potential of direct and indirect exposures and illicit use of ARs on public and community forest lands have recently raised concern for fishers (Martes pennanti), a candidate for listing under the federal Endangered Species Act in the Pacific states. In an investigation of threats to fisher population persistence in the two isolated California populations, the authors investigate the magnitude of this previously undocumented threat to fishers; they tested 58 carcasses for the presence and quantification of ARs, conducted spatial analysis of exposed fishers in an effort to identify potential point sources of AR, and identified fishers that died directly due to AR poisoning. Forty-six of 58 (79%) fishers were found exposed to an AR, with 96% of those individuals having been exposed to one or more second-generation AR compounds. No spatial clustering of AR exposure was detected, and the spatial distribution of exposure suggests that AR contamination is widespread within the fisher’s range in California, which encompasses mostly public forest and park lands. Additionally, four fisher deaths, including a lactating female, were diagnosed and directly attributed to AR toxicosis. The first neonatal or milk transfer of an AR to an altricial fisher kit was documented. These ARs, some of which are acutely toxic, pose both a direct mortality or fitness risk to fishers, as well as a significant indirect risk to these isolated populations. Future research should be directed toward investigating risks to prey populations that fishers are dependent on, exposure in other rare forest carnivores, and potential AR point sources, such as illegal marijuana cultivation in the fishers’ range on California public lands.

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ELECTRONIC FILE - Zoology

CSE-style citation: Gabriel MW, Woods LW, Poppenga R, Sweitzer RA, Thompson C, Matthews SM, Higley JM, Keller SM, Purcell K, Barrett RH, Wengert GM, Sacks BN, Clifford DL. 2012. Anticoagulant rodenticides on our public and community lands: spatial distribution of exposure and poisoning of a rare forest carnivore. PLoS ONE. 7(7):e40163. doi: 10.1371/journal.pone.0040163.