The barred owl’s westward migration threatens other species and a whole ecosystem

Barred owls, native to the eastern United States and Canada but invasive to the west, prey on a wide range of species with special conservation status.
Photo Credit: Lane Wintermute/USFWS

A new study of nearly 800 barred owls on the West Coast shows the invasive predator feeds on 29 species given special conservation status by federal and state governments.

The list includes mammals, birds, fish, amphibians and reptiles, according to an analysis led by researchers at the University of Wisconsin–Madison, who describe the wide-ranging pressure the owl’s advance into new territory is putting on native prey and predator species alike.

In 2024, the federal Fish and Wildlife Service adopted plans to reduce the number of barred owls in California, Oregon and Washington to protect a pair of threatened owls, the northern spotted owl and California spotted owl.

The new findings, published before peer review as a preprint on bioRxiv, suggest that the barred owl — which arrived recently in the western United States — is a danger to the survival of more than just competing owls, according to Daniela Arenas-Viveros, a lead author of the study.

Barred owls spread west across Canada with help from people. UW–Madison researchers have collected animals in three invaded states on the West Coast to document their diets.
Image Credit: Peery Lab

“The barred owl has a direct impact on spotted owl, and that has been studied very well. But we have reached a point where the science goes beyond that,” says Arenas-Viveros, a researcher in the lab of Zach Peery, UW–Madison professor of forest and wildlife ecology. “We are talking about barred owls affecting a whole ecosystem and all sorts of species.”

Barred owls, with wingspans that can reach 4 feet and generalist tastes in prey and habitat, are native to the eastern United States and southern Canada. In western Canada and western United States, they are an invasive species. But they don’t necessarily fit a common understanding of invasive animals like pet pythons escaping into the wild in Florida or jumping worms arriving from other continents in soil with imported plants.

“People didn’t carry the barred owls there like we have with insect pests of agricultural crops,” says Peery, a coauthor of the new study. “But we created the environment that allowed them to expand their range dramatically into the west.”

That was most likely by suppressing wildfires and nearly wiping out bison, allowing trees necessary for nesting to appear on the otherwise grassy Great Plains, Peery says. The warming of central Canadian forests has also made them hospitable bridges to the west for the barred owl.

“They’re native to Wisconsin, in our backyard. They’ve evolved here over the course of millions of years,” Peery says. “But they are a novel, exotic species in the western United States, and they’re having detrimental impacts on biodiversity.”

Invasive barred owls consume 29 species that hold federal or state conservation status, according to findings in California, Oregon and Washington by UW–Madison researchers.
Image Credit: Peery Lab

The research team — which included collaborators at the U.S. Geological Survey, Sierra Pacific Industries, and the Integral Ecology Research Center and the Hoopa Valley Tribe in California — tallied 162 species consumed by 788 individual barred owls in California, Oregon and Washington, identifying them by isolating the DNA of prey in the contents of the owls’ digestive tracts.

The barred owls were lethally removed and collected under state and federal permits from a range of forest types from 2015 to 2024 in the course of studies assessing the effect of managing the barred owls for the benefit of native spotted owls. But the new study shows the barred owls spreading down the West Coast are eating already at-risk species of frogs and salamanders; protected raccoon-like ringtails; shrinking populations of bats, chipmunks, quail and snakes; and disappearing fish like the federally threatened coho salmon.

“This is a single snapshot in time, just the most recent feeding event from each of these birds,” says Emily Fountain, a research scientist in Peery’s lab and coauthor of the study. “If you can detect 29 of these species of concern in just a single recent feeding event for all of these owls, there is a good chance repeated sampling would show they are consistently eating more.”

Among the species eaten by barred owls in the study are at-risk fellow birds of prey like the northern harrier, long-eared owl and western screech owl, and ground-based predators including the ringtail.

“Those animals are getting double the pressure,” says Fountain. “They’re eaten by the barred owl and the barred owl is eating their prey.”

It adds up to damage that could reach far beyond spotted owls.

“Public perception can get tunnel vision. We are trying to widen that, to help people understand there are many other native species, many of them with their own conservation plans, that are threatened further by the barred owl,” Arenas-Viveros says. “And this is time-sensitive, because they have not stopped expanding into new places.”

Funding: Support for this research included funding from the Department of the Interior and NASA.

Published in journal: bioRxiv (preprint)

Title: Thinking past owl vs owl: The barred owl invasion threatens ecological communities in the western United States

Authors: Daniela Arenas-Viveros, Emma Fehlker Campbell, Amy L. Munes, Hollis Howe, Hermary M. Gonzales, J. Mark Higley, Daniel F. Hofstadter, Brendan K. Hobart, Greta M. Wengert, Angela Rex, Brian P. Dotters, Kevin N. Roberts, Christina P. Varian, M. Zachariah Peery, and Emily D. Fountain

Source/Credit: University of Wisconsin–Madison | Chris Barncard

Reference Number: eco111125_01

Privacy Policy | Terms of Service | Contact Us