Over the last 20 years, the number of people visiting Utah’s Canyonlands National Park has more than tripled. Does this affect desert bighorn sheep, or do they get used to all the vehicles, mountain bikers, and hikers? New research shows that hikers have the biggest impact on the sheep, which flee more than half of encounters with people on foot.
“Hikers cause the greatest disturbance to bighorn sheep,” say Christopher Papouchis, who did this work at the USGS in Fort Collins, Colorado, and is now at the Mountain Lion Foundation in Sacramento, California, and his co-authors in the July issue of the Journal of Wildlife Management. Human recreation has been implicated in bighorns abandoning habitat elsewhere in Utah as well as in Arizona and California.
To determine how increased human recreation affects desert bighorn sheep (Ovis canadensis nelsoni) in Canyonlands National Park, Papouchis and his colleagues studied a population of about 250 sheep living in the Island in the Sky district, an approximately mile-high plateau bounded by the Colorado and Green River canyons. The researchers observed more than 1,000 bighorn sheep responses to vehicles, mountain bikers, and hikers from spring to fall during two years.
Papouchis and his colleagues found that hikers caused the strongest response. Bighorns fled far more often during encounters with hikers than with vehicles or mountain bikers (60 percent, 17 percent, and 6 percent, respectively). Bighorns also fled quite a bit farther (about 100 m) from hikers. Why the difference? Nearly all hiker encounters were off-trail, making them less predictable than encounters with vehicles and bikers. Moreover, the off-trail hikers often surprised bighorns by approaching them directly to see or photograph them.
“It’s not hikers per se but rather hikers that approach sheep,” stresses Papouchis. “Several studies have found that heavy trail use did not seem to bother sheep because the hikers were in a predictable location.”
The effect of hikers was seasonal: during the fall males were more responsive to hikers, and during the spring females fled three times farther from hikers (an average of 470 m vs. 140 m).
“We recommend managers confine hikers to designated trails during autumn rut and spring lambing in desert bighorn sheep habitat,” say Papouchis and his co-authors.
The researchers also found that while some bighorns near the heavily used road were habituated to human activity, most tended to avoid it. This effective reduction of suitable habitat could limit the bighorn population.
Papouchis, C. 2001. Responses of desert bighorn sheep to increased human recreation. Journal of Wildlife Management 65:573-582.