<figcaption> Credit: © DAVID HANSON</figcaption>

The vast majority of wildlife biologists want to protect animals, as does Rocky Gutierrez, a University of Minnesota researcher who studies barred and spotted owls. Part of his next experiment, however, could involve killing barred owls.

Barred owls are often blamed for out-competing and possibly even preying on their threatened relatives, the spotted owls. The barred owls' movement across the Rocky Mountains and down the west coast of the United States has coincided with a dramatic drop in the numbers of native spotted owls. "There's a lot of concern that the barred owl is having a negative impact," says Gutierrez, who was the senior author of a recent white paper on the options for researching the owls' interactions (see www.sei.org/owl/Buchananetal.pdf). "But in order to understand whether or not they really are doing it, you need to do an experiment."

The experiment Gutierrez is proposing would...

"I actually think that most scientists would generally be in support of that if it had all of the components of a really good experiment," says Barry Noon of Colorado State University. However, "it may also be possible to take better advantage of what I would call a natural experiment," Noon says, by comparing spotted owl occupancy or reproductive success in areas that are very similar except for the presence of barred owls. "I don't know whether that potential has been fully explored," he says.

The paper written by Gutierrez and colleagues outlines seven different research and management tactics for exploring the relationship between the two owl species, including observing their ecological interactions, intervening in habitats or feeding, and disrupting barred owl reproduction. "The one that's getting all the attention right now in the media is the removal option," says coauthor Eric Forsman of the USDA Forest Service, "but the one I'm most interested in is the option to look at competitive interactions between barred owls and spotted owls," for example, by studying the species' home ranges, diets, and habitats.

"Some of the ecological studies would be really valuable," agrees Joseph Buchanan of the Washington Department of Fish and Wildlife and lead author of the white paper. But several of the options he and his coauthors explored, he says, "were either not very useful or would take a tremendous amount of time," such as trying to alter owl habitat experimentally or offering barred owls food to try to draw them away from spotted owl ranges.

Removing invasive species, or even a native species that's threatening other animal populations, is fairly common, says Robin Bown of the US Fish & Wildlife Service, although it's often approached as a management technique rather than as a research experiment. Feral cats and Norway rats have been removed from islands with seabird colonies, for example, and foxes and even skunks have been controlled to allow ducks and other water fowl to breed.

Programs to manage brown-headed cowbirds in North America have been controversial, in part because evidence linking cowbirds to declines in the populations of other passerines has been ambiguous, a result Gutierrez thinks could be avoided with the proper experiments on the owls.

No matter how an experiment is done, or what might be learned from it, managing spotted owl populations in the long term by controlling barred owls would be a daunting if not impossible task. "As a research experiment? Yeah, maybe," says Forsman. "But in terms of management, I simply think that there's not a whole lot that we can do to stop the range expansion of the barred owl."

If removal experiments were to be performed with barred owls, it's not yet clear exactly what such removal would mean. "Most scientists would personally prefer not to [kill the animals]," Gutierrez says, but "it's clearly the cheapest and easiest thing to do."

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