Since ancient times, owls have been called many things, such as mysterious. These birds can be found in many parts of the world. And today, one kind of owl is causing a problem in forests of the northwestern United States.

Barred owls are a large species native to eastern North America, but they began moving west at the start of the 20th century. By 1973, large numbers of barred owls had arrived in the western state of Washington. Later they moved south into Oregon and California.

In parts of the Pacific Northwest, the owls are now believed to be causing a drop in the population of a smaller, less aggressive bird: the northern spotted owl.

In many ways, the barred owl is the spotted owl's worst enemy. The barred owl has more babies per year and eats the same animals, like squirrels and wood rats. And their numbers are now larger in many parts of the spotted owl's traditional territory.

In this Oct. 23, 2018 photo, Dave Wiens, a biologist who works for the U.S. Geological Survey, walks through a forest near Corvallis, Oregon.

David Wiens is a biologist with the U.S. Geological Survey, a federal agency that studies the Earth and its natural resources. He and other officials are doing something unusual to protect spotted owls: killing barred owls.

It is a controversial, experimental program. More than 2,400 barred owls have already been shot.

Wiens is the son of a well-known bird expert and grew up with a fascination for birds. He has mixed feelings about the program.

"It's a little distasteful, I think, to go out killing owls to save another owl species," he says. But he adds, "We knew that barred owls were outcompeting spotted owls and their numbers were growing too fast."

To catch barred owls, officials put digital bird callers on the ground. Then they step back and wait as several sounds from the devices fill the air. All of this happens in the dark of night.

Barred owls dislike other birds in their territory, so they will fly down and chase other owls out. That is when Wiens and his team try to shoot them.

The federal government has been trying for years to save the northern spotted owl. Some years ago, this bird was at the center of a huge battle over logging rights across Washington, Oregon and California.

In 1990, the northern spotted owl was listed as threatened under the Endangered Species Act, and appeared on the cover of Time magazine. Then, officials suspended logging on millions of hectares of forests to protect the bird. But the spotted owl population continued to fall.

During that time, researchers began to study another threat: Larger, more aggressive barred owls were competing with spotted owls for food and space and pushing them out of some areas.

Now comes this final effort to see whether the government can save spotted owls.

The U.S. Fish and Wildlife Service launched the experiment a few years ago. It has raised questions, such as: How much is it possible to reverse a drop in population that has been happening for years, caused in part by human activity? And, as climate change continues to push species out and affect how and where plants and animals live, how much should people get involved?

Just as with other conservation measures that involve killing one animal to save another, the program has also led to legal questions and debate. Still the Fish and Wildlife Service has a permit to kill up to 3,600 owls and, if the program works, could decide to expand its efforts.

In four small study areas in Washington, Oregon and California, Wiens and his team have been killing barred owls to see whether the native birds return to their land once their competitors are gone. Small efforts to remove barred owls in northern California and Canada's British Columbia have shown promising results.

Wiens now sees his gun as a research tool. He said that, by getting involved, humans "may be able to achieve more biodiversity in the environment, rather than just having barred owls take over and wipe out all the prey species."

But not everyone agrees.

Marc Bekoff is a professor of ecology and biology at the University of Colorado, Boulder. He strongly opposes the experiment and says humans should find another way to help owls. Bekoff notes that there is no way to see it as a good thing "if you're killing one species to save another."

Michael Harris directs the wildlife law program for Friends of Animals, a nonprofit group. He thinks the government should direct its attention on what humans are doing to the environment and protect habitats rather than blaming barred owls.

Some Americans see a responsibility to get involved. They note that humans are to blame for activities like logging, which helped lead to the drop in spotted owl numbers. But other people just see a losing situation.

"A decision not to kill the barred owl is a decision to let the spotted owl go extinct," said Bob Sallinger. He is conservation director with the nonprofit Audubon Society in Portland, Oregon.

If reducing the barred owl population improves the number of spotted owls, the U.S. Fish and Wildlife may consider killing more barred owls as part of a longer-term effort. Enough success has been noted that the experiment already has been extended to August of 2021.

Phuong Le reported this story for the Associated Press. Alice Bryant adapted it for VOA Learning English. George Grow was the editor.

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