(CN) – Biologists warn in a study released Tuesday that northern spotted owls, long endangered by logging operations in the Pacific Northwest, face another threat: competition from the invasive barred owl species.
The research, published in the journal The Condor: Ornithological Applications, found that the northern spotted owl’s habitat is rapidly being taken over by barred owls, a more aggressive bird that has pushed out the endangered species, taken over its hunting grounds and occasionally killed them.
The northern spotted owl’s number began to decline in the 1980s with the expansion of the logging industry. It wasn’t until 1990 when the species was listed as threatened under the Endangered Species Act. A subsequent 1991 court order stopped logging in national forests where the species was found.
Today, only about 560 pairs can be found in Northern California, with 1,200 pairs in Oregon and 500 pairs in Washington state. In British Columbia, Canada, there are fewer than 100 pairs. Wildlife conservationists estimate the populations have declined 40 to 90% in the past four decades due to loss old-growth habitat.
The new threat to the northern spotted owl’s survival is the barred owl. Study author Connor Wood, doctoral student at the University of Wisconsin, and his team deployed audio recorders in an area more than 3,700 square miles in two national forests in Northern California.
Using the audio recordings, they were able to detect owl calls used by barred owls to determine how far spread the species had become. They discovered a 2.6-fold increase in territory occupied by barred owls in 2017 and 2018, forest habitat that had traditionally been home to the northern spotted owl.
Barred owls have been able to take over more land because they are more adaptable than northern spotted owls and create more offspring.
“Wood and his colleagues believe their results show that the growth phase of the Barred Owl population in the region is just beginning, meaning wildlife managers still have time to act,” the authors said in a statement.
Wood recommends removing some barred owls from the Sierra Nevada stronghold of northern spotted owls to determine if it can stem the tide.
“We suggested that managers act according to the Precautionary Principle: when there is a serious threat to human health or the environment, proactive responses are justified even if there is some uncertainty,” Wood said.
“We feel that experimental barred owl removals in the Sierra Nevada are an important step in determining the best long-term management strategy. This is not something that anyone takes lightly, but we feel that it is warranted because of the very real possibility that continued barred owl population growth could seriously endanger the California spotted owl.”
In 2010, the federal government explored whether killing barred owls might help the spotted owl population, but no plan was put into effect.