From: Andy Soos, ENN
Published April 13, 2012 09:43 AM

The Owl "Fight"

The spotted owl is a species of true owl. It is a resident species of forests in western North America, where it nests in tree holes, old bird of prey nests, or rock crevices. Barred owls habitats are dense woods across Canada, the eastern United States, and south to Mexico. In recent years it has spread to the western United States. Recent studies show suburban neighborhoods can be ideal habitat for barred owls. High densities of invasive barred owls appear to be outcompeting the threatened northern spotted owl for critical resources such as space, habitat, and food, according to a study released today by Oregon State University. The three-year study — conducted in western Oregon through a research partnership including the U.S. Geological Survey and OSU —also confirms that barred owls not only use similar forest types and prey species as spotted owls, but also that a high density of barred owls can reduce the amount of those resources available to spotted owls.

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"Interactions between invasive and native species can be multifaceted and complex, with the stakes being even higher when the native species is already threatened with extinction," explained USGS Director Marcia McNutt. "Careful scientific observation and analysis can tease out the critical areas of conflict or competition, the first step in finding solutions."

The Spotted Owl is similar in appearance to the Barred Owl but has cross-shaped markings on the underparts, whereas the Barred Owl is alternately barred on the breast and streaked on the belly. Barred Owls are larger and grayer than Spotted Owls. In recent years the California and Northern subspecies of Spotted Owl have been displaced by Barred Owls, which are more aggressive, have a broader diet and occur in more varied habitats.

The northern spotted owl was designated as threatened under the Endangered Species Act in 1990. 

Barred owls also have become more common than spotted owls in the forests of western Oregon, according to David Wiens, the USGS author of the study. Within the study area at least 82 pairs of barred owls were identified but only 15 pairs of spotted owls.  The probability that spotted owls survived from one year to the next was 81 percent compared to 92 percent for barred owls, and barred owls produced more than six times as many young as spotted owls.

The value of old forest habitat for spotted owls was further demonstrated by the study.  Both species frequently used patches of old conifer forest or stands of hardwood trees along streams while hunting for food and roosting, and both species survived better when there were greater amounts of old conifer forest within their territories.

The study occurred in the central Coast Range of western Oregon where barred owl populations have steadily increased over the past two decades. Of all of the owls identified in the study area, Wiens captured a sample group and outfitted 29 spotted owls and 28 barred owls with radio transmitters. He monitored the interactions among the radio-marked owls and how the two species used resources. The forested area where the study occurred included 52 sites that were formerly occupied by pairs of spotted owls. 

In February 2012, the U.S. Fish and Wildlife Service released a draft Environmental Impact Statement that outlines options for experimental removal of barred owls from certain areas throughout the spotted owl's range to test the effect of such removal on spotted owl population trends. The Service is considering combinations of both lethal and non-lethal (capturing and relocating or placing in permanent captivity) methods for removing barred owls.

For further information see Competitive Interactions or USGS

Spotted Owl by Patrick Kolar image via Oregon State University

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