For two similar species to successfully coexist in a landscape, they need to share. This process of “resource partitioning”—when competitors co-occur in a landscape by varying how, when, or where they obtain resources like food and habitat—is especially critical to the conservation of threatened and endangered wildlife. The northern spotted owl is one such species, and its populations are in decline from a combination of old-forest habitat loss and competition by a nonnative and aggressive cousin, the barred owl. Over the last 50 years, the barred owl has expanded so far into northern spotted owl territory, that its geographic range now completely overlaps that of the threatened and more specialized northern spotted owl.
A recent study published in the journal Scientific Reports provides the first evidence that these two species of owls rely on different forest elements within their overlapping territories. This information may help managers actively promote forest structure that benefits spotted owls over barred owls.
Led by Julianna Jenkins, a postdoctoral research wildlife biologist with the U.S. Forest Service’s Pacific Northwest Research Station, the study used telemetry data from radio-collared owls in western Oregon’s Coast Range from 2007 to 2013 to monitor how the animals used the landscape for foraging. Remote sensing data were used to describe forest canopy structure and topography.
The researchers found that while both species used tall-canopy areas more often than low-canopy areas, spotted owls were more commonly found in areas with lower tree cover, more developed understory, and steeper slopes.
“Our goal was to identify any differences in the species’ habitat use that may facilitate long-term coexistence,” said Jenkins. “We think spotted owl space use may be compressed to these narrower forest types in response to their competitive interactions with barred owls.”
Knowing which habitat elements are used by each species, managers can actively promote forest structure to benefit spotted owls over barred owls.
“We can’t realistically remove every barred owl from a landscape, but we can alter forest structure through land management,” Jenkins said. “By manipulating vegetation in old forests’ mid- and understories, we might help to reduce competitive interactions between the owl species and facilitate co-existence and long-term persistence of spotted owls.”
The study is in collaboration with the U.S. Geological Survey, University of Washington, and National Council for Air and Stream Improvement.