HARRISON, Neb. — Optimism bounds on the spring legs of bighorn lambs in western Nebraska.
But life as a bighorn is as precarious as the rugged ridges they roam.
There are more than 80 new lambs in Nebraska's five wild herds of Rocky Mountain bighorns so far this spring. Newborns arrive almost daily, delighting wildlife biologists.
Newborns weigh 8 to 10 pounds and walk within hours after birth. Within a few more hours, they're scampering around the rocky slopes, sometimes bounding across the backs of their reclining — and tolerant — mothers.
Mountain lions, coyotes, bobcats and golden eagles pose natural threats to young bighorns, but their steepest challenge is disease, especially pasteurella pneumonia. The respiratory ailment is a ruthless killer of bighorns.
Pneumonia is common in livestock. Cattle and sheep producers easily treat their corralled critters with antibiotics, but it's not practical for wildlife biologists to round up free-ranging bighorns for a similar dose of medicine.
The Nebraska Game and Parks Commission started reintroducing bighorns to the state in 1981. The sheep are considered an at-risk species and are closely monitored. Wildlife biologists watch the herds for signs of pneumonia. They listen for coughing. They watch for lethargy.
Major outbreaks of the bacterial pathogen have decimated herds in Nebraska. It happened at Fort Robinson State Park, where half the herd's rams, ewes and lambs died in 2005. Two years later, the epidemic hit again, killing half the remaining sheep. Last year, only one of 12 newborn lambs at Fort Robinson survived. Nearby at Barrel Butte, only three of 31 lambs survived. Pasteurella pneumonia was suspected in most of the deaths.
Nationally, pneumonia epidemics kill countless bighorns from Nebraska to California, according to the Wild Sheep Foundation in Cody, Wyo.
Kevin Hurley, the organization's conservation director, compared the epidemics to diseases that ravaged American Indian populations in the first centuries of the continent's settlement by Europeans.
“They had no immunity or resistance,” Hurley said. “In a lot of places across the West, we see single-digit lamb retention by the time they approach their first year. In some herds, only one or two lambs survive.”
Antibiotic and vaccine research is widespread. Researchers in Colorado, Idaho and Washington have looked into everything from “bullets” packed with antibiotics to lacing feed and mineral blocks with the drugs. The bio-bullet was a dud. Treating feed and minerals hasn't been effective because bighorns prefer to eat greening grasses in spring and summer — when pneumonia hits — rather than baited feed, said Todd Nordeen of Alliance, the Nebraska Game and Parks Commission's regional wildlife manager.
“It's a tough time of year to get them interested in eating anything else because they have so many other food sources out there,” he said.
Injecting bighorns with antibiotics created for livestock is effective, but delivering the drug to a wild animal isn't simple. Using a dart gun, Nordeen injected an ailing Fort Robinson bighorn with an experimental drug last year. The female was the only survivor of a group of sheep sick with pasteurella pneumonia.
“We'll try to hit a few more this year,” Nordeen said.
Nordeen darted two adult sheep in the Cedar Canyon herd with an antibiotic seven years ago. They were the only survivors in a band of about 25 bighorns.
“The antibiotics are out there, but we're wrestling with how to deliver them,” he said. “Darting isn't practical because the sheep are elusive and timing is critical.”
Antibiotics are not a cure, but they help ailing sheep over the hump and prolong life, Nordeen said.
Lambs usually don't succumb to the disease until they quit nursing.
“That's typically when it seems to hit and we see them die,” Nordeen said.
Nebraska wildlife biologists have noticed no signs of the disease so far this spring, but they typically don't at this stage.
“We're starting out good, which is the way we often see it,” Nordeen said. “But when we get to a period when the lambs are nursing a little less, we'll start seeing losses. I almost guarantee it.”
Not all Nebraska herds suffer annual die-offs. The new Sowbelly Canyon herd near Harrison — relocated from Canada last year — and the Hubbard's Gap herd in the Wildcat Hills along the North Platte River have recently avoided pneumonia deaths.
The Hubbard's Gap herd started with 51 sheep relocated to private land from Montana in 2007. Despite early pneumonia deaths, the herd has been Nebraska's most successful in terms of growth. If this year's lamb crop matches the numbers added in 2012, the McGrew-area herd could grow to about 180 sheep.
Despite setbacks from disease and poor lamb survival in some bands, Nebraska had an estimated 345 bighorns — a record population — in five herds before the start of lambing season. There were no bighorns in the state as recently as 1980.
Nebraska's bighorn lambing season typically starts in late April. Most are born in May and June. Ewes typically give birth to one lamb.
Laura Woodrum of Crawford, a Game and Parks conservation technician who watches the Sowbelly Canyon herd, said the group birthing behavior is a carryover from Canada, where the sheep faced more predators.
Woodrum has observed two lambing seasons in Sowbelly Canyon. Both years, ewes in a band near Pants Butte gathered on the side of a rocky bluff, protected by walls of rock above and below. They remain in the relative safety of the remote location for several weeks after giving birth and then leave together.
Until they depart, the narrow terrace is both nursery and playground.
The lambs rear up on their hind legs and butt heads. They tussle over rock pinnacles.
“There's a lot of ripping around,'' Woodrum said. “The antics are practice for the future.”
Kylie Cone of Scottsbluff, who monitors herds at Hubbard's Gap and Cedar Canyon, said the lambs learn how to avoid predators as they dash along the edges of cliffs.
“The way they charge around this crazy environment of unstable, rain-slick and crumbly rocky outcroppings, just 24 hours after being born, just boggles my mind,'' she said.
Nordeen said spring lambing as prairie grasses are greening is a natural time to be hopeful about the future of bighorns in Nebraska.
“You hope you're on the path for another good year and get over some of these humps,” he said. “But in bighorn sheep management it's a lot of ups, downs and slow progress.”
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February 2012: Journey ends, story begins for bighorns