Canyonlands’ Pandemic Closure: Bighorn Sheep Returned to the Road, and Lambs Thrived

Desert bighorn sheep are some of the most iconic animals in Canyonlands National Park, but loss of habitat along the park’s four-wheel-drive roads, specifically the White Rim Road, poses a significant threat to their future. When the pandemic closed the park in 2020, Bill Sloan, a wildlife biologist at Canyonlands, Arches and Death Valley national parks who has studied bighorn sheep at 27 NPS units over four decades, spent seven weeks informally observing how the sheep used the road with no visitors or traffic on it. Those observations, published in Park Science in summer 2022, showed sheep returning to areas they had abandoned for decades, and ewes producing far more lambs that survived the summer despite a drought year.

Three pregnant ewes feed undisturbed on green vegetation along a four-wheel-drive road in Canyonlands, with no recreational traffic. NPS / W. B. Sloan.

Why the road matters

Between 1980 and 2016, recreational use in Canyonlands increased by 1,362 percent. The effect of disturbance on wildlife is hard to measure: some animals spend more time scanning for danger and less time looking for food, and long, intense disturbance can shift how wildlife use habitat in ways that go unnoticed until the habitat is abandoned altogether.

A 1993–1994 study by Sloan and colleagues found that the sheep spent more time alert to streams of traffic and less time foraging, and appeared to flee as traffic built up day after day. As the day went on they reached a threshold of cumulative stress, avoided the road corridor altogether and moved to habitat with poorer food. The 2001 paper from that study recommended limits on White Rim Road use, which led to the park’s current permit system, limiting the number of road users each day all year.

The road corridor matters because it has the highest-quality forage seasonally. Ewes in their third trimester need the nutrients in tender, green, emergent vegetation to carry a healthy lamb to birth, but earlier studies showed that recreational disturbance makes sheep avoid the corridor, potentially reducing the number of newborns that survive.

What the closure showed

Canyonlands and the other National Park Service units of the Southeast Utah Group closed to the public for nine weeks, from March 27 to May 28. Sloan used the White Rim Road’s closure as an informal chance to build on earlier research. The sheep he saw stayed close to the road: of the 65 observed during the closure, 42 were within 1.1 miles of it, 34 of those were within half a mile, and seventeen of those used habitat within a quarter mile.

He saw nine individuals along the roads, some feeding only on greening vegetation, and photographed tracks and scat of several groups and many individuals. The sheep apparently fed along the road at length while undisturbed.

For several days he watched a maternal group of six return to an area the sheep had left after four campsites were developed there; he had last seen sheep in it in October 1993. They fed and bedded among the campsites and along the road. A group of ewes was feeding on newly emergent green grass right beside the road. Neither group was bothered by Sloan’s unobtrusive presence, even when they came within 65 feet at times.

A maternal group crosses a four-wheel-drive road at White Rim backcountry campsites on April 22, 2020. NPS / W. B. Sloan.

A collared ram moved from the White Rim to the Island in the Sky mesa top, an area sheep had used in the mid-1990s but abandoned as traffic grew on the main paved road that bisects the habitat. After two decades and several generations of sheep avoiding it, they were immediately comfortable again once the traffic stopped. The ram stayed near the road in a group of eight until the park reopened, then moved over a mile away from it.

Preliminary GPS data from collars before, during and after the closure also appear to show collared animals staying much closer to the roads while the closure lasted, and moving around less.

After the reopening

Midsummer visits climbed sharply once the spring closure ended, and by fall visitor totals were at record numbers: up 30 percent in October, 67 percent in November and 76 percent in December compared with 2019. September through December 2020 were all record-setting months. During this time Sloan documented a significantly greater disturbance response from the sheep, measured by time spent alert and distance fled, and repeatedly saw their vigilance and flight increase.

After the reopening, alert rams graze along the White Rim Road as disturbances make them wary. NPS / W. B. Sloan.

An approaching vehicle sends the sheep fleeing once their threshold was reached; they had grazed along the road for two hours. NPS / W. B. Sloan.

Lambs

Lamb survival was excellent throughout 2020 despite extreme drought. Nearly every ewe tracked with a GPS collar had a surviving lamb. By the end of October the overall ratio was 80 lambs per 100 ewes, against an average closer to 35 per 100 over the last three decades. It is possible, if not likely, Sloan writes, that the absence of disturbance during the spring lambing season let pregnant ewes find more nutritious food; a future study could check that more rigorously.

What he recommends

To protect the fragile sheep population on the White Rim Road as visitation and recreational pressure rise sharply, Sloan recommends seasonal camp closures, reduced vehicle and bike traffic, a lower permit level, and restrictions on climbing and off-trail hiking. Seasonal closures or restrictions would run from March 1 through August 31 each year, to remove stress and reduce flight during the lambing period, a time of heightened sensitivity.

He plans further research on how far recreational traffic keeps sheep from the vegetation along the road corridor, whether it causes abandonment of suitable habitat, and what energy costs disturbance-driven flight imposes on late-stage pregnancy and lamb survival.

Sources

• National Park Service, Park Science 36(1), Summer 2022, “Perspectives”: William B. Sloan, Bighorn Sheep Reclaimed Abandoned Habitat during the Pandemic and Had Lots of Young. Now What?; the author’s portrait is left out, and the source’s “26 years” for the campsite area is not used because it disagrees with its own 1993 date; rewritten in hubnx's own words.