Which pair are the two endangered species most affected by pesticides in Colorado?

• A. Black footed ferret; Peregrine falcon
• B. American bison; Bald eagle
• C. Prairie dog; Mountain lion
• D. Grizzly bear; Swift fox

Answer: (A)

Pesticides affect wildlife in two big ways: direct toxicity and through the food chain, where predators accumulate poisons from their prey. The black-footed ferret is extremely vulnerable because it feeds almost entirely on prairie dogs and depends on their burrows for shelter. When pesticides are used to control prairie dogs, the ferrets can be poisoned by eating contaminated prey or carcasses, or by secondary poisoning, which can seriously hinder recovery of this already endangered species.

The peregrine falcon is a top predator that relies on other birds for food, so it accumulates pesticide residues present in those prey species. Historically, DDT caused eggshell thinning and failed reproduction, driving severe declines in peregrine populations. Even after DDT’s ban, residual pesticides can still affect their reproductive success in some areas. This combination of vulnerable ecology and pesticide exposure makes these two species among those most affected by pesticides in Colorado.