The federal government killed 4 million animals last year as part of the duties of the Department of Agriculture's Wildlife Services, which intervenes when animals become a threat.

The number, which tends to fluctuate and rose last year, comprises "75,326 coyotes, 866 bobcats, 528 river otters, 3,700 foxes, 12,186 prairie dogs, 973 red-tailed hawks, 419 black bears and at least three eagles, golden and bald," according to The Washington Post.

The agency usually deals with invasive species such as feral hogs, giant swamp rats called nutria, Argentine lizards called tegus and starlings; however, native animals can also be killed if they become a threat.

In one example, birds at about 800 airports around the country are killed so they don't clog the gears in airplanes, Wildlife Services spokeswoman Lyndsay Cole told the Post.

According to a data chart, most of the complaints that animals were causing damage or posing a threat were related to property and agriculture, followed by health and safety.

Wildlife Services works with government agencies around the country to deal with conflicts between humans and wildlife.

"As wildlife damage increases, requests for assistance also increase," said spokeswoman Carol Bannerman, as quoted by the Post.

The kill total can be as low as 1.5 million or as high as 5 million per year. Because Wildlife Services doesn't keep detailed data about why and how the animals are killed, two members of Congress have called for greater transparency.

Rep. Peter A. DeFazio (D-Ore.) has described the agency as "one of the most opaque and obstinate departments I've dealt with," the Post reported.  

The Center for Biological Diversity filed a petition last December that demanded Wildlife Services provide exact reasons why each native animal is killed, why the kill is beneficial and how the animal is killed.

The petition described Wildlife Services as "a rogue agency" that was "out of control," according to the Post. 

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