The U.S. Fish and Wildlife Service has pulled the trigger on a plan to kill more than 450,000 barred owls over 30 years to keep the northern spotted owl from being driven out of Oregon and Washington.

Animal-welfare groups promised to sue to stop the plan. Wildlife officials said they didn’t make the decision lightly. Barred owls will weather the onslaught, but spotted owls are at a crossroads, they said.

“This isn’t about choosing one owl over the other. If we act now, future generations will be able to see both owls in our Western forests,” USFWS Oregon State Supervisor Kessina Lee said in a statement.

USFWS Pacific Region director Hugh Morrison signed the decision, capping two years of planning. USFWS opted for a plan calling for killing more than 15,000 barred owls a year for three decades — up to 452,583 in all.

USFWS plans to shoot barred owls in the Cascade Range, Olympic Peninsula, Willamette Valley, Oregon Coast Range and elsewhere in Southern Oregon and Northern California.

Barred owls are protected by the Migratory Bird Treaty Act, and USFWS issued itself a three-year permit to kill them. The program will have to sustain political and funding support for more than a generation.

USFWS did not provide an estimate of how much the operation will cost. Factors affecting costs will be complex, and USFWS can’t accurately estimate them, USFWS spokeswoman Megan Nigel said in an email.

USFWS categorizes barred owls as a “non-native organism” crowding out the northern spotted owl in Oregon and Washington and beginning to encroach on California spotted owls in Northern California.

Animal-welfare groups said barred owls are expanding their range, as species have always done, and accused USFWS of single-species myopia.

The agency’s strategy violates norms about the proper treatment of North American owls, Wayne Pacelle, president of Animal Wellness Action and the Center for a Humane Economy, said in a statement.

“The agency is stepping onto a killing treadmill that it can never dismount,” he said.

USFWS ranks barred owls and habitat loss as the biggest threats to northern spotted owls, which were listed as a threatened species in 1990. Despite cutbacks on logging on federal lands, the spotted owl continues to decline.

Without thinning barred owls, northern spotted owls are likely to be driven from the Northwest, and California spotted owls are likely to be harmed next, according to USFWS.

Barred owls are slightly bigger and more aggressive than spotted owls. They eat the same rodents as spotted owls, but also feed on amphibians, insects and mollusks, giving them an edge in forming denser populations.

Barred owls migrated from east of the Mississippi River and showed up in the Northwest about 60 years ago. Climate change may have helped them cross Canadian forests, according to USFWS.

The shootings will take place over 28% of the northern spotted owl’s range, leaving alone barred owls in a majority of the spotted owl’s range, according to USFW.

USFWS plans to employ “removal specialists” armed with shotguns to draw barred owls within shooting range by playing recordings of the barred owl’s distinctive call, which sounds like the phrase “Who-cooks-for-you.”

In places where firearms aren’t allowed, barred owls will be lured into traps by plastic owl decoys or live mice and then euthanized, according to the strategic plan.

USFWS initially estimated that once a decade one spotted owl would be accidentally shot. Upon further review, the agency concluded even that may overestimate the risk to spotted owls.

Meanwhile, only a fraction of the world’s barred owls will be killed, according to USFWS.