Wichita ? Federal wildlife inspectors have found hundreds of dead birds in a piece of equipment common to the oil drilling industry that officials had not suspected caused migratory bird deaths.

For years, wildlife inspectors have worked closely with oil producers to reduce bird deaths in open pits and open tanks, but no one realized heater treaters were a danger to migratory birds until the agency received a complaint from a rural resident of Pratt County, said John Brooks, special agent with the U.S. Fish and Wildlife Service.

“I don’t think anybody really realized how big a problem this could be – and certainly the Service was not aware of the bird deaths taking place in heater treaters,” Brooks said Wednesday.

The equipment is used routinely in oil fields to separate gas, oil and saltwater pumped from the ground. Heater treaters are enclosed cylindrical stacks that are typically about 20 feet tall and 5 feet in diameter with a 6-inch to 8-inch wide exhaust stack.

Birds had apparently been flying into the exhaust stack, he said.

After receiving the complaint, Brooks said he inspected the heater treater and found carcasses in it, which prompted him to check 10 other heater treaters in the area. He found about 25 more dead birds in half of them.

Brooks assembled a task force of federal wildlife inspectors who were paired with agents from the Kansas Department of Parks and Wildlife to inspect heater treaters in Kansas oil fields for violations of the Migratory Bird Treaty Act of 1918.

In two days, they inspected 150 heater treaters, finding the remains of between 350 and 400 birds in about half of them, he said.

“It is a significant number. … It is something of a concern,” Brooks said.

Many of the carcasses were too decomposed to tell what kinds of birds they were, but they included meadowlarks, flickers, starlings and blackbirds, among others, he said.

Jon Callen, president of the Kansas Independent Oil and Gas Assn., said the economic impact should be minimal because screens to keep birds out could be installed relatively inexpensively.

“I think the number (of bird deaths) surprises us because we never stop to think of it on a larger scale,” said Callen, who is also president of Wichita-based Edmiston Oil Co. “We only stop to think of it in terms of our own equipment … not thousands across several states.”

Wildlife officials have given Kansas oil producers until of the end of this year to fix the problem, Callen said.

He estimated it would cost between $100 and $150 per heater treater to pay for the screen and labor it will take to retrofit the devices.

“On an individual scale, it is not something we can’t manage,” Callen said.

But because thousands of Kansas oil producers use the devices, the cost statewide for the industry will likely be more than $1 million and could reach as high as $10 million in Kansas alone, he said.

Federal wildlife officials in Kansas are in the “early stages” of getting the information disseminated throughout the agency nationwide, Brooks said.

“Kansas isn’t the only state that has this kind of equipment. … It is just one of those things for us to wake up to on the national level,” Callen said.