WILD NEIGHBORS: Owl Versus Owl, or Playing God in the Old-Growth Forest

By Joe Eaton
Thursday March 01, 2012 - 03:04:00 PM
Barred owl in Everglades National Park.
Chris Harshaw
Barred owl in Everglades National Park.
Spotted owl in Humboldt Redwoods State Park.
Ilya Katsnelson
Spotted owl in Humboldt Redwoods State Park.

Word has been out for a while about federal plans for lethal control of barred owls in the range of the endangered spotted owl, but the first media coverage I’ve seen was a short Associated Press article on page A12 of Wednesday’s Chronicle. The story covered Interior Secretary Ken Salazar’s announcement of a new critical habitat designation for the northern spotted owl, oddly described (by the AP writer, not by Salazar) as a “passive, one-pound bird”, and a concurrent plan to remove “selected barred owls.” 

This is not going to go over well with a lot of people, including some in the conservation community. 

If you look at the actual Interior press release, the barred owl control program is supposed to be detailed in a separate Environmental Impact Statement to be released in March. The accompanying fact sheet presents it as an experimental approach rather than a wholesale slaughter. The EIS, the agency says, will “outline options for removing barred owls by lethal or non-lethal methods, such as capturing and relocating or placing in permanent captivity,” to be followed by evaluation of the effects, if any, on spotted owl populations at the experimental sites. That analysis might lead to barred owl removal on a broader scale. 

This kind of experiment is exactly what some spotted owl researchers have been calling for. In a 2007 article in the journal Biological Invasions, R. J. Gutierrez of the University of Minnesota and co-authors wrote: “…it seems evident to us that carefully designed removal experiments are our best hope for rapidly determining whether declines in some spotted owl populations are being caused by barred owls…As scientists concerned with endangered species or invasive species, we feel that the only way to inform the public of their full range of options is to understand the effect of barred owls on spotted owls by experimentally removing barred owls from areas where spotted owls are declining to determine whether they are the root cause of the declines.” 

A cynic might wonder if the barred owl is being presented as a scapegoat for the timber management policies that have eliminated much of the spotted owl’s old-growth forest habitat. However, it seems clear from field surveys in Oregon and elsewhere that spotted owl populations have contracted as barred owl populations have expanded. 

The barred owl is a common Eastern bird. I believe the first non-captive owl I ever saw was a barred, in some Georgia or Florida swamp, and I heard them long before I saw one. Southerners hear the owl’s call as “Who cooks for you? Who cooks for you-all?” (This is not the place to get into the semantics of “you-all,” on which Roy Blount Jr. and others have written extensively, or whether the owl has it right.) 

About 80 years ago, barred owls began expanding westward. They crossed the Rockies, reached the Pacific Northwest—home of the northern subspecies of the spotted owl—and moved south, crossing the Oregon/California border in 1981. Barred owls have been present at Muir Woods since 2002. They’ve also occupied the Sierra range of the California spotted owl, although at lower densities than in the Northwest. The third spotted subspecies, the Mexican spotted owl, is unaffected as yet. 

How exactly would one owl species displace another? While I would not buy the characterization of the spotted owl as passive—it is, after all, a predator--the larger, stronger barred owl is indeed a more formidable bird. Direct predation is one likely pathway of interaction. E.H. Forbush once found the remains of a long-eared owl in the stomach of a barred owl; the long-ear in turn had eaten an eastern screech-owl. 

Barred owls can lay more eggs per clutch than spotted owls, although it’s not clear that they consistently fledge more offspring. 

Spotted owls are specialist predators, with a limited menu of flying squirrels and woodrats; barred owls will eat anything that moves (see above.) While spotted owls are tied to old growth, barred owls do fine in cutover forests and second growth. Short of predation, there are anecdotal accounts of barred owls bullying spotted owls. The two species also hybridize, with at least 50 documented instances between 1974 and 1999—a trend that may accelerate as spotted owls become rarer. Looks like a classic case of competitive exclusion, which is an old story. Ask any Neanderthal. 

Gutierrez and colleagues do acknowledge some Rumsfeldian known unknowns: “…we do not know in detail, or with any degree of precision, the rate of barred owl range expansion, the magnitude of the increase in population density, the rate of colonization of different forest types or the nature of interspecific interactions. More importantly, we do not know if declines in spotted owl populations are being caused or simply exacerbated by barred owls.” Hence the suggestion of removal experiments. 

This isn’t going to be cheap. In a 2010 article in Northwestern Naturalist, Kent Livezey of the US Fish and Wildlife Service estimates the cost of the projected removal study as a million dollars annually over a 3 to 10 year period, or $700 per barred owl during the first year and $2800 for each subsequent year. Livezey assumes a take of 2150 to 4650 barred owls, numbers conspicuously absent from the Interior press release. (I’ve only seen an abstract of the article so can’t say how close this is to what the Interior Department is about to propose.) 

So much for cost. Other considerations will be explored next week.