Hostile takeover

Eleven years ago, a biologist walking through Redwood National Park in Humboldt County, Calif., stumbled across the body of a northern spotted owl. Thin cuts the size and shape of talons sliced into its left side, puncturing the bird's lungs and heart. Whatever had eaten away the breast muscles had a delicate touch; there were no broken bones. The blood was still wet; the bird, neatly decapitated.

When the biologist came back several hours later, he heard hooting: "Who cooks for you. Who cooks for ya'll." Recorded barred owl calls brought a second round of hoots, and when the man mimicked a spotted owl, the barred owl flew in, speckled feathers still clinging to one of its feet.

Although the northern spotted owl made the cover of Time magazine, motivated environmentally minded college students to spend their summers hooting in old growth, inspired countless recipes for spotted owl stew, and sucked up more state and federal funds than any other threatened or endangered species, the bird is now in a steep, unanticipated tailspin.

And no one knows how to stop it.

In British Columbia, only 22 northern spotted owls remained in 2006. A few of those birds are being captured in the hopes of launching a breeding program and fending off extirpation. On the Olympic Peninsula in Washington state, the spotted owl is declining by more than 4 percent annually. No owls were born there last year. Scientists blamed a cold and rainy spring, but still: Zero is a hard number to spin.

One of the most likely contributors to the bird's decline is a newcomer to the Pacific Northwest. The barred owl, which has been moving in from the East, is bigger than the spotted owl and more aggressive. And it has been thriving as the spotted owl falters, leading to speculation that it's gobbling up spotted owls' food and hogging their nest sites. Occasionally, the barred owl mates with the spotted to create "sparred owls." In at least one instance, a barred owl ate a spotted owl.

The final Northern Spotted Owl Recovery Plan, released by the U.S. Fish and Wildlife Service in late May, calls for experiments in shooting barred owls to see if that might halt the spotted owl's decline. These studies would gauge the effect of the barred owls and pave the way for lethal control as a management tool. But the barred owl is a big, handsome bird, protected in its own right under the Migratory Bird Treaty Act. Some view its arrival as a non-native invasion caused by human activities, but others think it is merely a natural range expansion -- the kind of thing that will become more commonplace as the climate changes. Is killing one raptor to protect another a reasonable strategy? If not, what does the future hold for the northern spotted owl?

At Elkhorn Creek in early May, Oregon State University graduate student David Wiens hears the beeps of a radio-marked barred owl on his receiver. But he can't find the bird. He walks deeper into the forest, past flat-topped orange mushrooms and maples with still-crumpled leaves, along the length of a moss-covered log, until he's standing at the base of a large hemlock, antenna in hand, still unable to make out anything in the tangle of branches. Suddenly a barred owl heaves herself from the hemlock, flaps once or twice, and settles into a nearby tree.

For a moment, she's starkly visible, large and white and almost flashy in the green gloom. Her chest is marked by a cloud of speckles above long downward bands, like streaks of rain. Two round eyes and a hooked beak swim into view, then she vanishes again against the pale trunk.

Ten years ago, a barred owl was a rare sight in this part of Oregon; now, they outnumber spotted owls by almost three to one. Barred owls started inching toward the Pacific at the turn of the last century, perhaps making their way through forests that grew as humans suppressed fire, perhaps taking advantage of higher summer temperatures in altered habitat, perhaps using trees along creeks and rivers as pathways across the Plains. They marched through Canada and turned up in Washington and Oregon in the early 1970s. Now they inhabit the entire range of the northern spotted owl.

Spotted owls used to nest in a patch of old growth near Elkhorn Creek. No longer: A pair of barred owls has moved in. As a species, the barred owls like the damp and they've chosen a spot right by the stream where the female can catch crayfish to feed her fledglings.

Compared to spotted owls, barred owls have every advantage. They are as much as 15 percent bigger. Their young emerge earlier, and there are more of them: Barred owls average three owlets, while spotted owls usually hatch out only one or two. Wiens has radio-marked 10 barred owl females and 10 spotted owl females. Of these, all the barred owls are nesting, compared to only three or four of the spotted owls. Barred owls are not picky about what they eat, plucking up insects, frogs, shrews and moles, and they're not fussy about where they live, settling into suburbs as readily as remote wilderness. The spotted owl is much more dependent on rodents -- red tree voles, northern flying squirrels, and bushy-tailed wood rats. And it prefers old-growth forests, which are getting harder and harder to find.

To date, most of the evidence of barred owls bullying spotted owls is anecdotal. Wiens is trying to remedy that. For his dissertation, he's placing radio transmitters on about 50 birds -- 25 of each kind -- to track where they move, whether they compete for food and nest sites, and how they relate to one another. He's determined to unravel what exactly is going on in the treetops.

• Wildlife