Small Insectivorous Mammals

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Deer, coyotes, mountain lions, wood rats, gophers, and mice are just a few of the mammals that populate wildlands. They may be exposed to herbicides through contaminated food or water, as well as direct sprays, spray drift, and contact with treated vegetation.

The toxicity of herbicides to mammals has been better studied than for most other species because they are used as surrogates for human toxicity assessments. Studies on mammals allow for evaluation of a wide variety of parameters, including reproductive, developmental, and neurological effects in exposed populations, as well as effects on blood chemistry, organ weights, and body weight gain or loss.

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Reading the chart: For each bar, the labeled central value is the most likely estimate. The right end of the bar assumes worst-case conditions for all underlying variables; the left end of the bar assumes best-case conditions. Mitigation is advised if risk enters the red zone.

Taxa: Small mammals.

Assumptions: Terrestrial application of herbicide at half of the maximum rate on a representative product’s label (see Table 4-1); 10-100% of diet is contaminated.

Likelihood: Under spot applications it is unlikely that a significant portion of a small mammal’s insect-based diet could be contaminated. With broadcast applications over any sizable area (unusual for wildland management) contamination is possible for some small mammals.

Mitigation: Use low-volume applications and reduce the amount applied per acre. Don’t treat large contiguous areas all at once. Avoid treating plants when feeding by insects is likely.

Risk calculated as a function of: The inherent acute toxicity of the herbicide to mammals; the residue rate of herbicide on insects (which is proportional to the application rate). Except for glyphosate with the POEA surfactant, risks in this chart do not account for potential toxicity of any surfactants that are part of the product formulation or added to spray mixtures.

Methodology and sources

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