Northern Spotted Owl Recovery Information Site Barred Owl Threat
Encroaching Competitor Adds to Spotted Owl's Struggle
The U.S. Fish and Wildlife Service has identified competition from barred owls as one of two main threats to the northern spotted owl’s continued survival (habitat loss is the other). We have decided to conduct an experiment to test the effects of removing barred owls from certain areas of spotted owl habitat to see if it would benefit spotted owls. Removal of some members of a common species to protect or recover a rare species, while not unheard of, is not a typical management practice, and it is one we propose only in the most serious conservation situations.
Barred owls are native to eastern North America. It is believed they began expanding west of the Mississippi River around the turn of the 20th century. This could have been a natural range expansion or human-caused, or a combination of both. The most common theory is that the barred owl’s westward movement was caused by changes to the environment in the Great Plains as people increasingly settled there and dramatically altered the landscape. This may have removed natural barriers that previously inhibited the barred owl’s westward expansion.
Barred owls now outnumber spotted owls in many portions of the latter’s range. Researchers have seen strong evidence that spotted owl population declines are more pronounced in areas where barred owls have moved into the spotted owl’s range. Declines are greatest where barred owls have been present the longest. The U.S. Fish and Wildlife Service is concerned that without barred owl population management, the spotted owl is likely to go extinct in some parts of its range.
Barred owls are larger, more aggressive, and more adaptable than northern spotted owls. They displace spotted owls, disrupt their nesting, and compete with them for food. Researchers also have seen a few instances of barred owls interbreeding with or killing spotted owls. Because the spotted owl is already struggling due to its reduced habitat, the effect of the barred owl’s presence is “adding insult to injury.” An already vulnerable population has a much more difficult time withstanding dramatic changes in the ecosystem such as the encroachment of a competitor. A healthy population, on the other hand, has more flexibility to adapt to changes.
The goal of this experiment is to test the feasibility of barred owl removal to determine whether it improves conditions for spotted owls on a small scale. We will remove barred owls on less than one twentieth of one percent of the range of the barred owl. If the experimental removal of barred owls results in improved spotted owl populations, we may consider proposing wider scale treatments as part of a barred owl management strategy. We would initiate a separate environmental review, with an extensive public review and comment process before making any such decision.
This graph demonstrates the effect of a steady 2.9 and 5.9 percent population decline over time. The most recent data on the northern spotted owl reported a 2.9 percent rangewide population decline from 1992 to 2006 (Forsman et al. 2011); the northern study areas showed greater declines, averaging about 5.9 percent. While the actual annual rates are variable and likely to change, this graphic demonstrates the population trend if these rates of decline continued unchanged in the future.
Proportion of NSO territories occupied by barred owls,
Oregon Coast Range 1990 - 2008
As barred owl populations increase, spotted owl populations appear to decrease.1 This graph displays the number of surveyed sites occupied by spotted owls and the number of sites where barred owls responded.
1 We do not yet have data to directly measure barred owl populations, but we can track the number of spotted owl sites we survey where barred owls respond, a value that should follow the general barred owl population trend.