Project Update
Anticoagulant rodenticides (AR), one of the most common forms of lethal rodent control, have been detected in a wide variety of predator and scavenger species worldwide, raising concerns about the sources of exposure and potential negative effects on population persistence. These two questions are especially pressing in the Northeast U.S., where three states are currently considering more restrictive regulations on AR purchase and use. Dr. Jacqueline Frair, Master's student Georgianna Silveira (both at SUNY-ESF), and the WHP used fishers (Pekania pennanti) as a model species to investigate AR exposure and its impact on the population.
We tested fisher livers (n=597) collected through legal harvest from Pennsylvania, New York, Vermont, New Hampshire, and Maine for 11 AR. We compared test results to landscape features, such as urban and agricultural areas, and to region-wide fisher population trends. Fishers were highly exposed to anticoagulants, with ≥1 compound detected in 78.6% (n=469 tests) and >1 detected in the majority (55.2%, n=325). Wild and urban interface, or buildings interspersed with vegetated wildland, was the most significant predictor of fisher AR exposure, pointing to low-density, residential anticoagulant use as the main driver of fisher exposure, as opposed to use on farms or in densely urban areas. We also found that as AR exposure increased, the probability of trapping success decreased, given harvest records provided by New York, Vermont, and New Hampshire. Our results provide some of the first evidence of the negative association between population trends and chronic, high levels of AR exposure in wildlife.
Project Background
Anticoagulant rodenticides are commonly used to control rodent populations. However, other wildlife can be accidentally exposed either by consuming the bait or by eating the poisoned rodents (secondary toxicity).
In 2017, ten fisher livers collected in 2013 and 2014 and stored in the CWHL wildlife tissue bank were tested for the presence of anticoagulant rodenticides. Tissue bank samples are collected from animals submitted for either cause of death determination or training purposes in necropsy workshops or fur school demonstrations. Samples were tested for the most common compounds, including chlorophacinone, diphacinone, warfarin, brodifacoum, bromodialone, difenacoum, and difethialone.
The majority of the samples tested positive for brodifacoum, followed by bromodialone and diphacinone. Of the seven samples that tested positive for rodenticide, three of them were positive for more than one type. Because there is only one rodenticide in any one commercial product, it shows that these animals are being exposed multiple times over a short period to these compounds.
The toxicity of rodenticides is dependent on both the dose and the susceptibility of the species. Unfortunately, such toxicity data is not available for wildlife species. However, levels were high enough in two samples to suggest that rodenticide poisoning could be the primary cause of death.
