Spotted owl monitoring in Olympic National Park: 1992-2016

Gremel, Scott

This report summarizes progress on the northern spotted owl (Strix occidentalis caurina) monitoring program in Olympic National Park in 2016. Monitored spotted owl territories in the national park, together with those visited by the U.S. Forest Service Pacific Northwest Research Station in the surrounding Olympic National Forest, make up the Olympic demographic study area. This is one of eight study areas called for in the Northwest Forest Plan to estimate spotted owl population trends and monitor the effectiveness of the plan. Spotted owl territories in the NPS portion of the study have now been monitored for an average of over 24 years. In 2016, National Park Service personnel monitored a sample of 52 spotted owl territories (hereafter “sites”) to estimate rates of occupancy, survival and reproduction. Crews made 202 field visits, detecting spotted owl pairs at five sites and single spotted owls at three sites. At the eight sites where spotted owls responded, they were found on an average of 48% of monitoring visits. Crews banded two spotted owls, and observed ten previously banded spotted owls. One nest attempt was documented, where the pair fledged a single juvenile Data collected on eleven northern spotted owl demography studies 1985-2013 were analyzed at a workshop in Corvallis, Oregon in January of 2014. This analysis estimated a range-wide rate of population decline of 3.8% a year, and a 3.9% annual decline for the Olympic Peninsula. Rates of spotted owl territory occupancy on the Olympic Peninsula declined from 81% in 1995 to 21% in 2013. Barred owls (Strix varia) were first documented on the Olympic Peninsula in 1985, and have now been detected at 94% of the monitored spotted owl sites in Olympic National Park. Displacement by barred owls is now the primary threat to the conservation of spotted owls in protected areas. The presence of barred owls has had a negative effect on spotted owl territory colonization rates and a positive effect on spotted owl territory extinction rates. Spotted owls that persisted on territories following detections of barred owls both moved a greater distance from their initial locations and higher in elevation relative to sites where barred owls were absent. Spotted owls initially showed some ability to move within their territories to avoid barred owl competition, but barred owls have continued to occupy new portions of spotted owl sites each year. Models suggest that barred owls are less likely to occupy spotted owl sites on the steepest, driest slopes, and the movement of the remaining spotted owls to the steepest portions of their territories is making access and complete survey of the remaining activity centers more difficult.

Spotted owl monitoring in Olympic National Park: 1992-2016

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