When you hear the words "invasive species," what comes to mind? Perhaps it's the amber waves of cheatgrass and buffelgrass that have turned vast stretches of sagebrush and desert into a prickly, flammable hell. Or the hordes of minute quagga and zebra mussels now clogging water intakes and starving fish in Southwestern reservoirs. Or nutria, aquatic rodents that nosh on crops and burrow into dams and roadbeds in the Pacific Northwest. All these species have two things in common: Deliberately or not, humans brought them here from other continents and created the conditions that let them thrive. Now that these exotics threaten our lands and livelihoods, as well as the native wildlife, we're spending millions of dollars to shoot, uproot and poison them. Few question the ethics of eradicating these interlopers.

 But what if one native predator is pushing out another native predator -- one listed as endangered? Perhaps the range expansion is natural, or perhaps our timber-cutting, home-building, carbon-spewing ways are to blame. In either case, can we -- should we -- try to put things right?

 In this issue's cover story, Montana writer Kim Todd examines the plight of that most notorious of raptors, the northern spotted owl, blamed (unfairly) for clobbering the Northwest's timber industry in the '90s. The federal recovery plan for the threatened bird, released in May after years of lawsuits and political manipulation, estimates that it will take three decades and nearly half a billion dollars to get it off the endangered roster. The plan's authors lay a big chunk of the blame at the taloned feet of the barred owl, a similar but bigger and more adaptable raptor that's moving into the logged and fragmented old-growth forests once home to the spotted owl. The plan recommends experimenting with killing off barred owls to give their cousins a chance to recover.

 In many ways, the rise of barred owls reflects the "survival of the weediest." As we cut forests, divert rivers, and plant crops and cities, the wildlife species that thrive tend to be the ones that aren't fussy about where they live and what they eat (think coyotes, starlings, carp). Meanwhile, the more specialized creatures with specific needs fade away.

 If we want to keep specialists like the spotted owl around, we can no longer just "let nature take its course." Aggressive intervention -- whether it involves removal of competitors, supplementary feeding or captive breeding -- is an unavoidable component of endangered species conservation today.
 But such intervention can't be the only component. If we want something more than a petting zoo for endangered wildlife, we have to provide more healthy native habitat. The early drafts of the federal recovery plan for the spotted owl emphasized guns over habitat. Thanks to the protests of biologists, the final plan calls for significantly more acres -- 7.3 million -- of protected forests. That's a lot less than the 24 million acres envisioned under the 1994 Northwest Forest Plan, but it's better than nothing. It's an acknowledgment that blasting an entire parliament of barred owls won't save the spotted owl if we neglect to protect the rare and beautiful forests that the spotted owls -- and many other species -- need to survive.