Stress Test for the Spotted Owl

15 August 1997 8:00 pm

Sitting in the woods waiting for an owl to poop might seem like an unrewarding research assignment. But such tedious field work has enabled researchers to show that logging and roadbuilding can stress out the spotted owl, a threatened species that lives in old-growth forests in the Northwestern United States. The work, reported in this month's issue of Conservation Biology, has raised new doubts about the adequacy of government efforts to protect the owl.

While biologists can monitor an animal's stress by measuring stress hormones in blood, capturing and drawing blood from a wild creature can itself trigger a powerful stress response, biasing a study's results. To study the spotted owl, animal physiologist Samuel Wasser of the University of Washington, Seattle, and his colleagues adopted a stressfree technique he and others had developed a decade ago to monitor animals such as baboons: scoop up the animal's feces, which also contain stress hormones.

They measured levels of the stress hormone corticosterone in fecal samples collected from 16 pairs of spotted owls nesting on the Yakama Indian Reservation in Washington, and from about 150 other owls scattered across the Pacific Northwest. They found that male owls living within 0.41 kilometers of a major logging road or a patch of forest that had been clear-cut within the last 10 years had corticosterone levels almost two times higher than owls living more than 3 kilometers away. Because high stress levels can cut into life-span and reproduction, at least in laboratory animals, Wasser says the results--which he emphasizes are preliminary--raise some questions about the efficacy of federal regulations designed to protect the owl.

One prominent spotted owl biologist fiercely challenges the new study, however. "It is an interesting idea, but I don't trust the results," says Eric Forsman of the U.S. Forest Service's Forest Science Laboratory in Corvallis, Oregon. He says the study's sample size is too small for the researchers to conclude that factors other than logging or roads--such as prey availability--aren't responsible for the measured stress differences. He adds that there's no evidence that the owls' stress levels have cut into reproduction or survival.

A senior federal wildlife manager dismisses the criticism. "You always have dueling biologists," says David Frederick, Washington state supervisor for the U.S. Fish and Wildlife Service, which helped fund Wasser's study. "There is extraordinarily little data out there on disturbance, and now we have a tool that will help us address that issue."

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