A federal agency that kills nuisance wildlife is under attack from environmental groups, which say the agency’s use of poison and trapping in Idaho puts other animals at risk.

Last year, Wildlife Services killed about 3,300 mammals in the state. Coyotes were the most frequent target.

Four environmental groups have threatened to sue, and asked Wildlife Services to stop killing predators and using explosives to remove beaver dams until the agency conducts a thorough analysis of how other wildlife, including federally protected grizzly bears and bull trout, are affected by its actions.

Trapping and poison are indiscriminate killers, said Andrea Santarsiere, staff attorney for the Center for Biological Diversity. “They don’t differentiate between what wildlife is walking through the area,” she said.

Other groups who filed the notice of intent to sue were the Western Watersheds Project, WildEarth Guardians and Friends of the Clearwater.

The notice also criticized Wildlife Services’ approach to predators, saying the agency failed to acknowledge predators’ complex role in ecosystems.

For instance, killing coyotes – a frequent predator of livestock – also affects the survival rates of sage grouse, a species in decline across the West, the notice said. Coyotes keep populations of foxes, badgers and ravens under control, which benefits sage grouse survival, it said.

Wildlife Services is part of the U.S. Department of Agriculture. It grew out of federal predator removal programs designed to help the livestock industry take hold in the West. Wildlife Services describes its current mission as resolving conflicts “to allow people and wildlife to coexist.” But critics say the agency still puts too much emphasis on killing animals.

Carol Bannerman, a Wildlife Services spokeswoman, declined to comment, citing the possible litigation.

About 80 percent of the agency’s work involves dispersing or relocating problem wildlife, she said. Of the animals that are killed, more than half are invasive species, such as European starlings, which cause extensive crop damage.

“Managing damage is the goal, not the eradication of any native species,” Bannerman said in an email.

In the past 10 years, the agency has trapped and released 50 grizzly bears in Western states, Bannerman said. Its agents killed six grizzlies at the direction of wildlife agencies.

Incidental killing of wildlife is rare, according to Bannerman, who said that 25 non-targeted animals were killed in Idaho last year.