Crater Lake National Park Biological Sound Station Research: 2016 Annual Report

Mohren, Sean

Beginning in 1992 the wildlife team at Crater Lake National Park started implementing the US Fish and Wildlife Service northern spotted owl monitoring protocol to determine distribution, abundance, and reproductive success of northern spotted owls in Crater Lake National Park. As the years progressed, reductions in budgets, shifting priorities and increased awareness of safety has reduced our ability to implement this monitoring protocol, in its entirety, at the Park. In general, the wildlife staff is presently capable of implementing 1-3 noncompliance surveys at each known owl activity center in any given year versus the 6 surveys recommended in the US Fish and Wildlife Service spotted owl monitoring protocol. In addition, there is currently no staff time available to survey areas of the park that contains high quality habitat but is not currently listed as a known owl activity center. In an effort to help improve our ability to determine the occupancy and distribution of northern spotted owl and barred owl, an owl that directly competes with northern spotted owls for habitat and resources, the wildlife team began exploring the use of acoustic stations to help supplement our survey efforts. Based on the results of our 2012-2016 sampling efforts, we believe using acoustic stations to supplement traditional northern spotted owl monitoring methods provides us with a cost effective way to improve our ability to document the presence of northern spotted owls and barred owls at Crater Lake National Park. The 2016 survey effort represents our third year of full implementation and the details of this effort are described in this report. The primary goals for 2016 were to document northern spotted owls and barred owls at 1) known northern spotted owl activity centers and 2) areas of the Park that contain high quality spotted owl habitat. In the summer of 2016, 29 sound stations were deployed at 7 known northern spotted owl activity centers and 8 locations that were determined to have suitable northern spotted owl nesting habitat. In general we deployed 2 sound stations at each site for an average of 14.42 days. A northern spotted owl was recorded at only one acoustic station at the Thousand Springs site. Field crews implementing a limited number of surveys following the US Fish and Wildlife Service northern spotted owl survey protocol recorded northern spotted owls at Thousand Springs, Bear Bluff, and Grayback Ridge sites in 2016. The acoustic station at Bear Bluff recorded an unknown Strix species, but no definite northern spotted owl. No acoustic station was placed at Grayback this year due to a late snowpack that limited access. Barred owls were documented at 10 sites (48%) using acoustic stations. Of those 10 sites, 7 overlapped with locations where traditional field crew northern spotted owl surveys were conducted. Surveyors recorded barred owls at two of these sites. From the data gathered using the acoustic stations in 2016, as well as in previous years, it is clear that their implementation is a beneficial asset in monitoring for northern spotted owls and barred owls. Not only have they helped complement the US Fish and Wildlife Service standard surveys, they have also provided us a new tool to survey for northern spotted owls and barred owls in many new locations within the Park.