"We suggest that restrictions on hiking intensity should be considered for canyons with high levels of human activity," say Elliott Swarthout, who did this work while at the University of Arizona in Tucson and is now at the Cornell Laboratory of Ornithology in Ithaca, New York, and Robert Steidl of the University of Arizona in Tucson in the February issue of Conservation Biology.
The threatened Mexican spotted owl lives in coniferous forests in the Southwest and Mexico. In Utah, the birds nest, roost and hunt almost entirely in steep, narrow canyons. Hiking and other recreational activities along the canyon bottoms are highest from March-October, which overlaps with the owls' breeding season.
To see if hiking affects the owls, Swarthout and Steidl studied 10 nests during the breeding season in Utah's Canyonlands and Capitol Reef national parks, which had more than 400,000 and 650,000 visitors per year, respectively, during the two-year study period. The nests were 36-223 feet above the canyon bottoms, and the researchers observed the owls during a series of experimental "hiking treatments": a hiker passed under a given nest every 15 minutes for four hours during three time periods (early morning, mid-day and evening).
Swarthout and Steidl found that hiking primarily affected the female owls: notably, females spent nearly 60% less time on prey-handling activities such as feeding their young, and a third less time on daytime maintenance activities such as tending the nest, and preening themselves and their young. Preening is important to birds' health in part because it reduces parasites.