If killing one species could save another, should we do it?

The case of the spotted owl is unusual, however, because to the untrained eye it looks almost identical to a barred owl. The two species are so closely related that they sometimes mate and produce hybrid offspring. This forces us to reconsider important ethical questions: Is it moral to kill in the name of ecological balance and biodiversity? And if so, how do we decide which species are acceptable to target?

Field trials show that shooting barred owls can halt the spotted owl's decline, but there is no end in sight. The Fish and Wildlife Service's current plan would continue for 30 years and kill up to half a million owls – but it's clear that shooting would have to continue forever to save the spotted owl.

Stephen Pruett-Jones, an ecologist at the University of Chicago, said that while barred owls can interbreed with spotted owls, they are very different animals with different calls and diets. Spotted owls eat only certain small mammals, while barred owls can eat mammals, fish, amphibians, birds, insects and snails. Spotted owls are only adapted to life in old-growth forests; barred owls live in a much wider range of environments.

In the 1980s and 1990s, environmentalists used the spotted owl's Endangered Species Act status to argue that some of the Pacific Northwest's old-growth forests needed to be protected from logging. They succeeded, but the spotted owl's population continued to decline, falling by 80% in the last 30 years.

Scientists and birdwatchers have observed the larger and more aggressive barred owl taking up residence in the area, displacing the spotted owl for food and nesting. And it's not just the spotted owl that's at risk – the barred owl's spread could also harm the local screech owl and pygmy owl populations. Some scientists fear that human activities have both decimated the spotted owl population and accelerated the barred owl's spread.

Kent Livezey, a retired wildlife biologist with the Fish and Wildlife Service, argues that human activities have influenced the owls' ranges for millennia. This began when Native Americans in the middle of the continent used fire to clear land. As European colonists took over the area, putting out fires and building farms, towns and parks, they helped create a corridor of trees through which barred owls, along with many other birds, slowly spread westward.

Livezey said he is not opposed to killing a few barred owls in places where spotted owls can be saved. His concern is that the government's plan calls for culling in areas where thousands of barred owls live, so more animals will be brought in to replace those shot.

He fears the killings have another reason: Under the Endangered Species Act, the spotted owl is the only legal means of preventing logging from destroying what remains of the original forests. It would be far better to pass new laws to protect the forests than to kill thousands of owls.

The only place he sees hope for the spotted owl is the Sierra Nevada mountains. In other places, he says, shooting them would be a waste of money and would endanger the birds' lives.

A recent New York Times An opinion piece also argues against the killing, citing “genomic evidence that the barred owl has actually lived in the Pacific Northwest for thousands of years.” But that contradicts what all the scientists have told me, and the paper cited doesn't seem to support it either, so I called one of the authors, biodiversity researcher John Dumbacher.

He said the Times article misrepresented his work, which he said showed there was more genetic variation among barred owl populations than previously thought. “The data is clear at this point: The barred owl is an existential threat to the spotted owl,” he said. The spotted owl is “disappearing at a rate that baffles scientists.” If humans had not drastically decimated their numbers by destroying much of the old-growth forest they depend on for survival, they might have been better able to defend themselves against the barred owls.

“Science is aware of what is going on here,” said Dumbacher, “but it doesn't tell you what to do about it.” We need ethical arguments for that. The public should also have a say.

He said he has given public talks on the subject and people have different views. He understands people's resistance to killing charismatic creatures. He is not against either path, but both choices will have consequences. If we do nothing, he said, the only things left will be dandelions, raccoons and black rats – and a few other species that can adapt to environments destroyed by humans.

There may be no good way forward. What may be more important is to proceed wisely – to have an end goal, to learn from mistakes, and to do what we can to avoid this crossroads in the future.