Capitol Reef’s Bighorn Herd Faces Pneumonia: First Case in 2018, Good News in 2022

In August 2018 a bighorn lamb in Capitol Reef National Park’s backcountry was dying of what looked like pneumonia, and a test confirmed the first documented case of the disease in the park’s herd. The pathogen was the bacterium Mycoplasma ovipneumoniae. The herd began in 1996 and 1997 with sheep moved from Canyonlands National Park, and a 2022 survey brought good news: a lamb for every ewe.

Capitol Reef National Park’s bighorn sheep herd. Image credit: NPS / Chris Roundtree.

A herd brought back

Translocating sheep from Canyonlands restored bighorn to prime habitat that had been vacant since the native herd died off from human activities in the 1930s. The original 40 translocated animals grew to an estimated 130 by 2006, the last year a few of the surviving original sheep had active radio collars. Each year the herd grew steadily and spread into unoccupied ranges. Some sheep died from puma predation and other causes, such as vehicle collisions, but survival stayed high and the herd appeared to be disease-free.

The disease arrives

The sick lamb in 2018 had an open mouth, rapid breathing, nasal discharge, coughing and an emaciated body, and two ewes in its group were frequently sneezing. Scientists first isolated the pathogen in Australia in 1972, in domestic sheep, and researchers have since found it in many wild animals. The disease can be deadly and can predispose an animal to other respiratory infections, but much about it is still unknown. In the next three years park staff saw a few more sick and dying animals, which tested positive, and in the winter of 2021-2022 the park’s biologist saw more sheep with wracking coughs, nasal discharge and emaciated bodies. The park euthanized and tested one sheep, and tested another soon after its death, and both were positive.

Counting lambs

The outbreaks and the need for more information led the park’s biologist to secure year-end funding from the National Park Service for a lamb survival study in late June and early July 2022, with a follow-up in late September. Little is known about the virulence and lethality of the different strains of this emerging invasive disease, but monitoring early lamb survival can show whether it is active or latent in a population. Lambs at Capitol Reef are born from late April through early June. Virulent strains can decimate a herd by killing nearly all lambs within the first six to eight weeks, while weaker strains may allow recovery and build immunity against more deadly strains.

The park monitors wildlife with game cameras, and the winter 2021 deaths led staff to aim them at lambing habitat and bighorn movement areas near the fatalities. A wildlife biologist who knew the herd from its early years also hiked into remote study areas in the central part of the park, between the Chimney Rock-Spring drainage north of the Fremont River and Burro Wash, looking for tracks, scat and other signs and scanning with high-powered binoculars. Because the terrain is rugged and time was short, the surveys stayed in creeks, washes and ridges within six miles of a road, and groups were watched for up to four hours each.

Bighorn sheep captured on a remote wildlife camera at Capitol Reef National Park in 2022. Image credit: NPS.

What the 2022 surveys found

In midsummer 2022 the surveyor saw 25 individual bighorn sheep: 11 adult ewes, 11 lambs, one juvenile ewe and two yearling males. Most bighorn ewes have one lamb a year, so a lamb for every ewe showed that lambs were surviving well. Apart from one coughing and weak female lamb, no obvious health issues were seen in fourteen hours of observation over four days, and the cameras showed sheep with no nasal discharge, in good condition, and most ewes with lambs. A follow-up in September, limited by flash flooding and with sheep possibly avoiding the area because of a pair of mountain lions, covered seven sheep, again one lamb per ewe, with no health issues in eight hours of observation, and recent tracks showed three large groups of other sheep, with nine or more lambs surviving for as many ewes. The article calls it a good year for the herd, but the future is unknown.

A healthy, lactating ewe looks back warily. NPS / William Sloan.

A disease that crosses borders

The strain found in dead Capitol Reef sheep matched strains in bighorn sheep in the Bureau of Land Management’s San Rafael Swell Recreation Area, close to the park’s northern boundaries, which suggests that animals moving across the park’s borders share diseases. The pathogen was also recently found in Canyonlands National Park, the herd’s origin and originally thought to be disease-free. That raises questions: whether environmental stressors such as inadequate forage or loss of access to water make herds more susceptible, what management options exist for preventing or limiting the disease, how common it is across different public lands, which strains are present and what part stress from increasing recreation plays.

The article argues that answering them takes multi-agency research with several funding sources, because managing the disease for one herd alone is like bandaging a bleeding wound without knowing its cause. The most efficient way to gain the information is to capture and collar animals to track their movements and to take tissue samples for genetics and disease status, which is expensive but would let managers decide whether to remove sick animals, limit visitor pressure or take other action. Bighorn sheep, a living symbol of wilderness often depicted in Native American rock art, can also serve to indicate the health of natural habitats: if they can thrive, so can many other species.

Sources

• National Park Service, An Infectious Strain of Pneumonia Threatens Capitol Reef’s Prized Bighorn Herd, by William Sloan with Morgan Wehtje, from the “Perspectives” section of Park Science, Volume 36, Number 2, Winter 2022 (December 30, 2022); rewritten in hubnx's own words. The author’s first-person account of the necropsy, the author’s portrait and the biography are left out.