Anticoagulant Rodenticides on our Public and Community Lands: Spatial Distribution of Exposure and Poisoning of a Rare Forest Carnivore

Abstract

Anticoagulant rodenticide (AR) poisoning has emerged as a significant concern for conservation and management of non-target 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, we investigate the magnitude of this previously undocumented threat to fishers, we 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. We found 46 of 58 (79%) fishers 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, we diagnosed four fisher deaths, including a lactating female, that were directly attributed to AR toxicosis and documented the first neonatal or milk transfer of an AR to an altricial fisher kit. These ARs, which some are acutely toxic, pose both a direct mortality or fitness risk to fishers, and a significant indirect risk to these isolated populations. Future research should be directed towards investigating risks to prey populations fishers are dependent on, exposure in other rare forest carnivores, and potential AR point sources such as illegal marijuana cultivation in the range of fishers on California public lands.

Cholecalciferol plus diphacinone baits for vole control: a novel approach to a historic problem

“…However, rodents can develop a resistance to anticoagulants (e.g., Myllymäki 1995;Salmon and Lawrence 2006), and anticoagulants can pose some risk to non-target scavengers and predators, although this risk is primarily attributed to second-generation anticoagulants (Stone et al 2003;Gabriel et al 2012;Tosh et al 2012). Zinc phosphide poses very little risk to non-target scavengers and predators (Eason et al 2010) but does have a high risk of toxicity to non-target species that might consume the bait directly (Marsh 1987).…”

Epidemiology and symptomatology of long acting anticoagulant rodenticide poisoning

“…The latter exposures were brought to light in studies by Gabriel et al [44,45] who performed necropsies on and assessed for presence of anticoagulant rodenticides in the carcasses of VHF-tagged fishers (Pekania pennanti). It was determined that the cause of death in over 10% of fishers, a candidate for the endangered species list, was rodenticide poisoning.…”

Infectious Disease and Contaminants in Urban Wildlife: Unseen and Often Overlooked Threats

“…Even for mountain lions, which generally avoid urban areas (Beier et al 2010), more than 90 % of animals tested in urban landscapes in California (and > 75 % of animals overall) are exposed to ARs (Poppenga et al unpublished data). Bioaccumulation is especially a risk with SGARs because of their persistence in tissue, so nontarget wildlife contamination is becoming a widespread conservation issue (Eason et al 2002;Erickson and Urban 2004;Gabriel et al 2012).…”