A migrating bird pecks for horseshoe crab eggs among the crabs laying them at Port Mahon, Del. (Michael Williamson/The Washington Post)

Eight state attorneys general filed a legal challenge Wednesday to the Trump administration's bid to dramatically weaken the Migratory Bird Treaty Act, a century-old law established to protect birds.

The lawsuit, led by New York Attorney General Barbara Underwood, and supported by Maryland, New Jersey, Illinois, Massachusetts, Oregon, California and New Mexico, is an effort to stop the Interior Department from fully implementing a directive to its law enforcement division to forgive mass bird kills, even when the animals are threatened or endangered.

In accordance with a new interpretation of the act issued in April, the department informed its wildlife police that the slaughter “of birds resulting from an activity is not prohibited . . . when the underlying purpose of that activity is not to take birds.” For example, the guidance said, a person who destroys a structure such as a barn knowing that it is full of baby owls in nests is not liable for killing them. “All that is relevant is that the landowner undertook an action that did not have the killing of barn owls as its purpose,” the opinion said.

An even broader interpretation by the administration held that the act would no longer apply even in a catastrophe such as the Deepwater Horizon oil spill that injured and killed up to a million birds. Interior would pursue penalties under the Natural Resources Damage Assessment program, which is not specific to birds, and ignore penalties that could be levied under the act.

The department had pursued claims under the act in the past, the directive said, but “that avenue is no longer available.”

In a statement related to the lawsuit, filed in the Southern District Court of New York, Underwood called the administration reinterpretation “yet another giveaway to special interests at the expense of our states.” Underwood said the Trump administration “gutted the Migratory Bird Treaty Act — eliminating long-standing prohibitions on injuring or killing over 300 species of migratory birds that provide critical ecological, scientific, and economic value to New York.” Birdwatchers and other observers poured $4.2 billion into the state's economy in 2011.

The attorneys general hail from four states governed by Republicans and four by Democrats. Their lawsuit will be considered with another filed by the National Audubon Society in May.

Sarah Greenberger, a senior vice president for conservation policy at Audubon, called the state challenge a “welcome wind beneath our wings in the fight to keep this vital bird protection law intact."