AUTHOR BLOG: Tracking Yosemite’s Spotted Owls

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Tracking Spotted Owls in Yosemite National Park. Photo credit: S. Scherbinski

Stephanie Eyes

Linked paper: California Spotted Owl (Strix occidentalis occidentalis) habitat use patterns in a burned landscape by S.A. Eyes, S.L. Roberts, and M.D. Johnson, The Condor: Ornithological Applications 119:3, August 2017.

In 2005, I happily discovered the Student Conservation Association and that I could be an intern studying California Spotted Owls in Yosemite National Park. I accepted the internship and worked on a PhD student’s project investigating the effects of fire on California Spotted Owl occupancy. The final results from this study revealed that owl occupancy rates were similar between burned and unburned forest, but led to questions about how owls use the mosaic of post-fire patches. In 2010, the former PhD student, my graduate advisor, and I began our efforts to understand this question by capturing owls and affixing radio transmitters to them with the help of several technicians over the course of the three field seasons. By attaching a radio transmitter, we were able to use radio telemetry to triangulate the position of owls during nocturnal foraging bouts. Specifically, we wanted to know how owl foraging patterns are influenced by fire severity, fire-created edges, and other factors such as topography or distance to stream or nest/roost site.

After owls were captured, we set up our telemetry stations along the trails and roads surrounding our known owl roost sites. We went out in teams of two, each armed with a headlamp and an antenna, and worked to locate the owls within our burned sites. Once we initially identified that an owl was present with our antenna, we would split up, one person racing ahead so that we could get three different readings within ten minutes, each separated by about 200 meters, before the owl moved to a new foraging site. While I was relatively experienced with daytime radio telemetry, these nocturnal trail surveys posed a new challenge I enjoyed overcoming, and one time we encountered a curious mountain lion also using the trail searching for (I hoped!) something else.

Whenever we surveyed these trail sites, I remember wondering what the owl was hunting in the burned mosaic of forest patches at the moment that we were trying to pinpoint its location. I’m hoping all my wondering what they were eating will encourage me to go through all the pellets we found in burned forests!

After all the data was collected and analyzed, we learned that owls exhibited habitat selection for locations near roosts and edge habitats, as well as weak selection for lower fire severities. Our results highlight the importance of sustaining forests burned with a mosaic of fire severities with smaller patch sizes of high severity fire. Maintaining this complex mosaic of forest patches and focusing on protecting roost site locations may help sustain California Spotted Owls in the greater landscape.

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