By Joe Eaton
Friday March 09, 2012 - 02:23:00 PM
Does the northern spotted owl face extinction by assimilation? Credit:
US Fish and Wildlife Service (via Wikimedia Commons.)
Does the northern spotted owl face extinction by assimilation? Credit:

Last week I wrote about a new proposal by the US Fish and Wildlife Service to study the impact of the barred owl on the endangered northern spotted owl by experimentally removing, lethally or otherwise, barred owls from selected sites where the two species overlap. The barred owl, a common and widespread Eastern species, has invaded the range of its close relative and appears to be displacing it in some areas. The two owls are interbreeding, raising concerns that the spotted owl may be genetically swamped by the larger, more fecund, and more adaptable barred owl. 

A few environmental groups have weighed in on the removal experiment. Steve Holmer of the American Bird Conservancy noted that FWS is also pushing additional timber-thinning projects, ostensibly for fire prevention, in spotted owl habitat. “The Fish and Wildlife Service is proposing a very carefully thought-out experiment to see whether removing hundreds of barred owls will benefit spotted owls,” said Holmer. “We’d like to see the same determined effort to assess the effect of forest thinning on owl populations, but the agency’s current recommended plan of action doesn’t include that.” 

The response from Washington State’s Olympic Peninsula Audubon Society was equivocal: “At some point, conservationists may have to debate whether, or how, to manage the barred owl to maintain the vitality of the spotted owl. In the immediate future, conservationists probably can work together to support funding for ecological studies of barred owls accompanied by removal experiments.” 

Portland Audubon, noting that feedback from members overwhelming opposed lethal control of barred owls, struck a cautious position: “Portland Audubon's position is that the highest priority must be placed on preventing the extinction of species even to the degree that this entails lethal control of other protected species. To that degree we support moving forward with the EIS, but will not take a final position on lethal control until we are able to fully evaluate the different options presented. We must see that the fundamental cause of spotted owl populations declines, loss of critical habitat, is being adequately addressed, that lethal control of barred owls, in addition to habitat protection and restoration, is a necessary condition for spotted owls to recover, and that such an approach is practicable and will substantially improve the spotted owl's chances for survival.” 

I’m sure other precincts will be heard from. 

The idea of culling one species to protect another does raise some thorny philosophical questions. To begin with, both birds are native North American species. We’re not talking about furriners like Asian carp or feral swine. We’re not even talking about North American species artificially introduced to another part of the continent, like eastern red foxes, wild turkeys, or bullfrogs in California. 

The brown-headed cowbird may provide a near analogy. This cuckoo-like brood parasite, originally native to the prairies, followed agricultural clearances into new territory where it found naïve hosts that had never evolved defenses against it; notable examples being the least Bell’s vireo in southern California. Cowbird eradication is a standard, and relatively noncontroversial, management practice for this and other endangered species. Likewise the selective culling of California gulls that prey on least terns and snowy plovers. 

But the dynamics are a little different in the owl case. It would be more straightforward if this was just a matter of predation. But, as FWS biologist Kent Livezey pointed out in a Northwestern Naturalist article, “control rarely is used to address competition and is never used to address hybridization.” 

For example, mallards have been generously sharing their genes with several related species: the American black duck, the mottled duck, and the Hawai’ian duck or koloa. No one is attempting lethal control of mallards beyond what happens, in an unsystematic fashion, during the duck season. Several other cases of genetic assimilation—the golden-winged warbler by the blue-winged warbler, the northwestern crow by the American crow—are being allowed to proceed without government intervention. 

Scientists are beginning to realize that hybridization among birds can sometimes give rise to new species, cases in point being the Italian sparrow and our own familiar Audubon’s warbler. You might well ask why we should interfere with the potential genesis of the sparred owl—or whether the two owls are distinct species, given that their populations are not reproductively isolated. 

The case for lethal control might be more convincing if the barred owl’s westward progress had clearly been assisted by anthropogenic changes to the landscape--by, for example, fire suppression in boreal forests or the planting of shelterbelts in the Northern Plains—which might create a presumption of human responsibility to deal with the results. As far as I know, this connection remains speculative. 

It might be reasonable, then, to err on the side of caution in any decision to choose sides in the owl wars. Stewart Brand, paraphrasing the British anthropologist Edmund Leach, launched his Whole Earth Catalogs with the pronouncement: “We are as gods and might as well get good at it.” That was 44 years ago, and there’s still room for improvement.