Counting sheep: Bighorns still struggling in southern Nevada

LAS VEGAS — Wildlife officials in Nevada say they’re seeing more wild desert bighorn lambs in the River Mountains east of Las Vegas, but the herd is still struggling with an outbreak of bacterial pneumonia that the animals have no natural way to fight.

An aerial tally in October counted 15 lambs per 100 ewes in the rugged area between Henderson and Boulder City, Nevada Department of Wildlife biologist Pat Cummings told the Las Vegas Review-Journal.

That’s more than twice the six-lambs-per-100 ewes found in 2015 but is still well below the average of about 33 lambs for every 100 ewes researchers say they find in normal years.

Biologists worry that enough lambs aren’t being produced to sustain affected herds.

“We’re just going to have to ride it out and see how individual sheep herds come through it,” state wildlife veterinarian Peregrine Wolff said. “Right now, unfortunately, it’s going to be kind of wait and see.”

Pneumonia has also hit bighorns in Washington state, Wyoming, Utah, Idaho and Montana, and threatens efforts to rebuild native populations that were on the brink of extinction a half century ago.

There’s no way to treat sick animals or vaccinate healthy ones against the illness, which might have originated in domestic livestock. It does not pose a risk to humans.

Wildlife officials say the pneumonia outbreak in bighorn herds in southern Nevada began as early as 2012 and got worse when a more virulent strain of the bacteria spread from sheep in Mojave National Preserve in California.

Blood samples collected from animals in the wild show the Mojave strain of the bacteria has spread into other herds in the Spring and McCullough mountains of southern Nevada — and across the Colorado River to bighorns in the Black Mountains in Arizona.

With no natural resistance to pneumonia, the animals tend to die when they get sick.

Animals that survive can become carriers of the bacteria, infecting newborn lambs in a cycle that can decimate a herd.

Bighorns once roamed nearly every mountain range in Nevada, but by the early 1960s the population had been reduced to about 1,200 animals as a result of unregulated hunting, habitat loss and disease from domestic livestock.

Since 1967, wildlife managers have restored Nevada’s official animal to more than 60 mountain ranges and helped boost the total population to more than 11,000 adults, more than any other state.