Bait and burrow fumigant rodenticides pose a particularly high risk of exposure to non-target species including endangered species. Toxic baits may attract feeding by non-target species and may pose risks of secondary exposure to animals feeding on poisoned pest species or carcasses. Burrow fumigants are non-selective for animals that live in burrows. Several endangered species of kangaroo rats (Dypodomys spp) are especially at risk from grain bait rodenticides because the common field-use toxicants are more toxic to kangaroo rats than they are to the target pest: California ground squirrel (Spermophilus beecheyi). Moreover, kangaroo rats are more efficient foragers for scattered grain baits. Among the stakeholders who collaborated to find practical solutions were experts in kangaroo rat biology and behavior. They proposed specially designed bait stations that excluded kangaroo rats, but admitted the more agile ground squirrel. Similarly, a bait station opening no larger than three inches effectively excludes the federally listed San Joaquin kit fox while admitting ground squirrels. Protecting listed species from secondary poisoning primarily depends on prompt removal of any carcasses that remain above ground. Maintaining regular control of pest species reduces total numbers of pests treated and lowers the total numbers of carcasses. Many non-target species occupy abandoned burrows of pest species and are at risk from burrow fumigant applications. However, non-target species are not expected to occupy burrows that are currently occupied by pest species. Field signs at the openings of burrows distinguish currently occupied burrows of pest species from those of non-target species. By limiting applications to burrows occupied by pest species, pests may be controlled while minimizing exposure to nontarget species, including several listed species of amphibians, snakes and mammals.

Protecting endangered species from exposure to rodenticides

248th National Meeting (2014)

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