After Humboldt, Ryan went on to work as a Wildlife Biologist for the US Forest Service in the Sierra Nevada.

  For his thesis, Ryan quantified the habitat relationships of Great Gray Owl prey in California montane meadows. More specifically, he investigated the influence of vegetative characteristics and cattle grazing on the density of voles and gophers. The Great Gray Owl has been listed as a California endangered species since 1980, yet information on the factors affecting owl prey is lacking. Ryan’s thesis helped fill this void and provided land managers with information needed to properly manage habitat for Great Gray Owl prey. The study was located in Stanislaus National Forest and Yosemite National Park, California.