Northern Spotted Owl Research

Since 1984, scientists have gathered data on northern spotted owl survival, occupancy, and reproductive success across federal lands in the Pacific Northwest. Long term demography provides a critical look into the success of the 1994 Northwest Forest Plan, which was implemented to ensure viable populations of northern spotted owls persist on the forested landscape. Demographic data closely tracks annual rates of population change and provides a way to evaluate the efficacy of federal action protecting this threatened species.
In 2020, the Lesmeister Lab conducted demographic research at five study sites and in 2021 monitored one study site, near Cle Elum. Our research focus has shifted to bioacoustic monitoring, a non-invasive method of collecting data on owl occupancy. A full transition to solely bioacoustic data will be complete by 2023. 
​Demographic research continues on many study sites previously tracked by the Lesmeister Lab. Federal partners and private collaborators continue to collect this valuable information.
Each of the eight study sites to the left were at one point surveyed by the Pacific Northwest Research Station. We now deploy ARUs at seven study sites – Cle Elum, Coast Ranges, Tyee, Klamath, H.J. Andrews, South Cascades and Northwest California.

A BIRD IN JEOPARDY

Although the Northwest Forest Plan has been critical in protecting the northern spotted owl, it is not enough to reverse rapidly declining populations. More robust conservation and management measures are necessarily to reverse the trend for spotted owls as they head toward extinction.

PUBLISHED FINDINGS

Research published by the Lesmeister Lab ​has been critical in tracking trends and threats to northern spotted ​owl populations.

A POPULATION IN DECLINE

Over thirty years of demographic data reveal a sharp decline in northern spotted owl populations, a trend attributed to habitat loss by logging and wildfire as well as to barred owl encroachment.

This range wide decline is detailed in a 2018 USFS synthesis of science chapter, as well as a 2021 meta analysis. Damon Lesmeister and colleagues argue that additional conservation measures must be implemented to protect remaining northern spotted owl populations.

IMPACT OF THE BARRED OWL

The barred owl, a fierce competitor of the northern spotted owl, has infiltrated Pacific Northwestern forests and pushed northern spotted owls off what remains of available habitat. Barred owls are considered an invasive species in the west.

Julianna Jenkins and colleagues illustrate how northern spotted owls disperse at greater distances in order to breed when barred owls are present. This behavioral change is associated to overall population decline, and both leave the northern spotted owl more vulnerable to extinction than they were thirty years ago.

BARRED OWL REMOVAL
Competitively dominant and invasive barred owls were actively removed from five study sites between 2009 and 2019. Removals occurred on treatment areas for three to six years (depending on the study area). As barred owls where removed from the landscape, the estimated mean annual rate of population change for spotted owls stabilized, showing only a 0.2% decline per year. This is compared to areas where barred owls were left alone and spotted owl populations continued to decline sharply (12.1% decline per year). These results demonstrate that the most substantial change to population dynamics of northern spotted owls over the past two decades are associated with the invasion and population expansion of barred owls. Now, the subsequent removal of the invasive species has the power to change the narrative.

SELECTION OF ACTIVITY CENTERS

LiDAR remote sensing can reveal the connectedness and heterogeneity of forest canopy cover. Recently retired lab member Stan Sovern demonstrates how data gleaned from LiDAR imagery can be utilized to accurately map spotted owl habitat. In a 2019 publication, spotted owls were found to specifically choose activity centers, and thereby nest sites, where the forest canopy was more variable on the surface and provided more overall cover.

PHOTOS FROM THE FIELD

​The Lesmeister Lab is based in Corvallis, Oregon and operates in a close partnership between the
U.S. Forest Service Pacific Northwest Research Station and Oregon State University. 

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