LAS VEGAS (KLAS) — Desert bighorn sheep are used to rugged conditions, but the drought has been hard on them and their numbers have dwindled in the Desert National Wildlife Refuge.

An estimate based on a 2021 survey indicates there were only about 470 desert bighorns on the entire refuge — about half the number counted in recent years. At 1.6 million acres, the refuge is the largest wildlife refuge in the lower 48 states, set up in 1936 specifically to preserve their habitat.

“That is a pretty serious contraction,” according to Pat Cummings, a retired Game Biologist for the Nevada Department of Wildlife. He cited estimates from 2019 that put the population at around 1,000.

The drought, now going on 22 years, has wildlife officials working hard to make sure the bighorns on the refuge have enough water. But that’s only part of the overall picture.

A complex problem

Christa Weise, acting director of the Desert National Wildlife Refuge, said there are more than 60 water sources on the refuge, and “currently about 40 water sources closely monitored and managed for desert bighorn sheep use.” The U.S. Fish & Wildlife Service is charged with managing the sprawling range.

Desert bighorn sheep gather around a water trough on Aug. 15, 2015. (Photo: Nevada Department of Wildlife)

Weise said most of the 40 water sources are “guzzlers” — rainwater collection systems. Others are springs or water seeps modified to collect water into tanks of drinking troughs that allow large animals access.

The current drought conditions come right behind an outbreak of bacterial pneumonia among the herds that began to occur in 2012, Cummings said. Pneumonia outbreaks hit lambs the hardest and can kill a lamb within 90 days after infection.

He said bacterial pneumonia involves a suite of different pathogens that vary from herd to herd. Each of the desert bighorn herds is dealt its own “poker hand” and the variants expand from there. While not as deadly for adult bighorns, he said pneumonia’s effect takes a toll.

A species management plan released in 2020 identifies the pneumonia problem as the biggest threat to desert bighorn sheep.

The drought doesn’t just make drinking water hard to find. It has also taken a toll on the plants that bighorns rely on for food. Often, it’s the food source that’s under attack by the heat. Bighorns eat native grasses and shrubs, and the lack of seasonal rains – particularly in late fall and early winter – is taking its toll on their food supply.

“There’s just not that much out there to eat,” Cummings said.

Doug Nielsen, Public Affairs/Conservation Education Supervisor for the Nevada Department of Wildlife, said the herds will move when necessary to go where they can find food.

Desert bighorns were rounded up in late June at Valley of Fire State Park — about 25 miles southeast of the refuge — and transported to the Skyrider Wilderness Ranch.

Adapted to the desert

Desert bighorn rams need don’t need a lot of water from day to day, but ewes need more when they are pregnant or lactating to feed lambs, Weise explained. “Desert bighorn sheep in hot and dry conditions may drink several gallons at one time. However, average daily need is under one gallon per day,” she said.

Weise said the amount needed by each animal varies depending upon animal size, water content and composition of food, and environmental conditions like humidity, daytime highs, and nighttime temperatures.

Cummings notes that it’s not just bighorns that are suffering. It’s all wildlife. Nielsen lists quail, rabbit, and other small species that are struggling through the drought.

A desert bighorn ram drinks at a water supply on Sept. 2, 2015. (Photo: Nevada Department of Wildlife)

Cummings talks about the experience of seeing a desert bighorn in the wild: “It’s a magnificent thing. It still gives me chills.” He talks about observing bighorns as they look out over their habitat – “scanning,” he calls it.

“It’s just majestic,” Cummings said.

A tip if you ever spot one in the wild: “They see so well … watch what they’re watching, because it’s probably other sheep,” Cummings said.

Volunteers to the rescue

In the midst of all this, conservationists are working hard to help bighorns survive. Projects to build guzzlers in remote areas of the refuge are a major undertaking, and they have to be coordinated with the U.S. Air Force because the range is almost entirely within the Nevada Test and Training Range.

The co-existence with Nellis Air Force Base training missions means helicopter flights to build — and replenish — guzzlers on the refuge must be cleared through the military. And that takes time, according to Weise.

Cummings says it’s a little mind-boggling to see all the work that goes into building a guzzler. Helicopters fly 900-pound tanks and all the construction materials in. Then crews are transported to the site. Eventually, a 40-by-80-foot apron is in place to collect rainfall to be stored in as many as four tanks.

This all takes a couple of days. “It’s like a symphony,” Cummings says. It’s the product of a lot of hard-working volunteers from organizations like the Fraternity of the Desert Bighorn. The organization is always looking for financial support for the guzzler program, and they sometimes need volunteers, too.

You can’t collect rain that’s not there, so through the drought, the need has grown to replenish guzzlers with water drops carried by helicopter.

“It takes up a lot of our money – and energy,” Weise said. But many of the people involved have a devotion to the project. After all, it’s for Nevada’s official state animal.

“They belong here, and there’s not many of them,” Cummings said.

Historical population levels

The refuge covers parts of Clark and Lincoln counties and includes six major mountain ranges. It is bounded on the east by U.S. 93, north to the Pahranagat National Wildlife Refuge. The public entry point to the refuge is just off U.S. 95 northwest of Las Vegas at the Corn Creek exit, about 30 miles from downtown Las Vegas.

With fewer than 500 desert bighorns scattered over 1.6 million acres, the chances of seeing one on the refuge aren’t good. And that’s part of the reason the species has survived. Exposure to domestic livestock, including goats and alpacas, increases the risks of disease in a population that has been isolated from other animals.

Statewide population estimates aren’t currently available, but in the late 1960s, numbers of desert bighorns dropped to around 2,500 in Nevada — and as low as 1,500 to 2,000, according to some estimates.

On the refuge, a pneumonia outbreak in 1988 severely decimated the bighorn herds, dropping the total population from 1,100 in 1988 to 200 animals by 1992.

Statewide, the population reached about 5,300 in 1993.

The bighorn population on the refuge was estimated at 900 five years ago.

“Bighorn sheep estimates on (the refuge) in 2019 and 2020 did not reflect a population contraction,” Cummings said. “Thus, the apparent population decline is seemingly more abrupt and evidenced by the findings through the most recent aerial surveys conducted in early fall 2021.”