National Forests serve many uses. Primary among their functions are to provide public enjoyment and to protect natural resources, including threatened and endangered species. Sometimes, these objectives conflict. In 2004 then Forest Service Chief, Dale Bosworth identified mismanaged recreation as one of the four biggest threats to public lands. However, surprisingly few well-designed studies have been conducted to address the impacts of recreation on wildlife and natural systems. This leaves managers to make decisions with little or no relevant information.

We are undertaking a ground-breaking study with local volunteer off-highway vehicle riders to test the impacts of motorcycle exposure on the federally threatened Northern spotted owl.

Effects of motorcycle exposure on the spotted owl will be assessed by observing owl behavior, measuring reproductive success throughout the season and assaying the levels of different steroid metabolites in owl scat before and after exposure to one hour of motorcycle exposure.

Partners in the study include Blue Ribbon Coalition, USDA Forest Service, US Fish and Wildlife Service, Student Conservation Association and the Center for Conservation Biology at The University of Washington.

The study design incorporates:

1. Monitoring spotted owls in territories near heavily used roads and in more remote areas to look for cumulative effects of vehicle exposure on physiology, behavior and reproduction throughout the season.

2. Experimentally applying hour-long “simulated enduro events” with volunteer riders to look for short-term changes in behavior and/or physiology after OHV exposure. Simulated enduro events involve three to five volunteer riders rising motorcycles back and forth past owl territories to mimic the level of traffic seen during the enduro events that occur five times annually in Mendocino National Forest.

Physiological measures are taken from owl scat collected non-invasively in the field. Principal investigator Sam Wasser extensively validated the laboratory techniques used to measure hormone metabolites in scat, and demonstrated that they accurately reflect levels in circulation. One hormone measured is corticosterone. Corticosterone is the primary stress steroid in birds and is elevated in response to a wide range of disturbance. Sex steroids like testosterone and estrogen will also be measured. Sex steroids are depressed in individuals experiencing chronic stress, and may indicate reproductive suppression. Other measures from scat include progesterone, which is related to parental care and thyroid hormone, which is tied to diet quality. Combined, these measures will give a comprehensive picture of owl health and should provide a reliable indication of whether and how OHV use affects the NSO.

The study will also investigate potential effects on owl behavior. Physiology and behavior will be compared before, during and after exposure for each individual NSO, so that each owl is its own control. Additionally, half of the pairs included in the study will never receive enduro treatment and will be used to control for potential time of day effects on behavior and physiology or potential impacts of researcher presence on the territory.

Because vulnerability to disturbance will likely vary with factors such as sex, reproductive stage and year, experimental treatments will be applied two times per year for three years. In order to increase sample size the study will include NSO in both Mendocino and Shasta-Trinity National Forests.

In 2007 the field crew includes two crew leaders, Zachary Folk and Jennifer Hartman and five Student Conversation Association interns, Eric DeRoche, Rayma Cooley, Takahiro, Dustin Detweiler, and Nick Politte. Lisa Hayward, Ph.D. serves as project manager. The success of the project also depends on participation of volunteers from the local OHV rider community.