South Dakota experts study fall in bighorn sheep herdsBiologists track yearling bighorn sheep as pneumonia hits Black Hills population.
By: Kevin Woster, Rapid City Journal
RAPID CITY (AP) — Josh Smith is on a trophy hunt for bighorn sheep these days.
But the 34-year-old graduate student in wildlife and fisheries science from South Dakota State University isn’t after regal bighorn rams with massive sets of horns. He’s after baby bighorn sheep, in hopes that they will live to become adults.
That’s a rare thing these days in most of the Black Hills, where pneumonia has cut the bighorn sheep population by more than half in recent years. Each vulnerable lamb that lives through its first year is a trophy of survival.
Smith has seen the ongoing die-off personally, as lead researcher in a project that uses radio-transmitter collars to follow bighorn herds and record lamb survival.
“It’s been a tough two years,” Smith said Tuesday. “Out of 53 collared lambs over the first two years of this study, I’ve had one make it alive up until right now.”
Actually, there were two survivors until a few days ago, when one of the 1-year-old sheep was hit and killed by a vehicle on U.S. Highway 385. That was truly bad luck for a young sheep that had been lucky enough — or genetically predisposed — to escape the pneumonia that has limited lamb survival throughout the Hills and devastated it in some areas.
The bighorn herd in Custer State Park is the most dramatic example of the problem. Going into the winter of 2004-2005, there were almost 200 bighorns in the 71,000-acre park. By the following fall, there were 48. And before the lambing season this spring, there were about two dozen.
The story hasn’t been all that much better in areas outside the park in bighorn herds that frequent areas from the west side of Rapid City up to Pactola Reservoir, as well as those south in the Spring Creek and Hill City areas.
Some sheep die from lion attacks. But pneumonia is big lamb killer, a biological predator that makes it so difficult for the herds to rebuild.
The research project, begun by SDSU and the South Dakota Game, Fish & Parks Department in 2010, was originally aimed at checking the mortality rates on bighorn lambs from lion predation.
But it soon became apparent that pneumonia was the bigger killer.
And it kills fast.
“In 2010, we collared 25 lambs and lost all of them,” said John Kanta, regional wildlife manager for GF&P in Rapid City. “In 2011, we collared 28 lambs, and two survived.”
Because the lambs were wearing radio collars, they could be found and examined in a laboratory setting, where the signs of bacterial pneumonia common in bighorns — and domestic sheep — were confirmed. Wildlife biologists believe that bighorn losses in the Hills from pneumonia are typically tied to contact between wild sheep and domestic sheep, an interaction that has been fatal to wild bighorns in large numbers throughout Western states.
A solution to that problem, including potential vaccines, is complicated and possibly far off. Meanwhile, GF&P and SDSU are trying to determine annual lamb survival and confirm the overall cause of death. That means finding and following the lambs, a process that began months ago, when bighorn ewes were captured and checked for pregnancy.
The pregnant ewes were fitted with a radio collar and a vaginally implanted device that would be expelled when the ewe gave birth and send out a different radio signal. Smith and others on the project were out day after day as the lambing season arrived to detect that signal, locate and collar the lambs.
There was little time to waste in getting that chore done, either, because the lambs get nimble in a hurry.
“If they get much more than 24 hours old, these things can scoot like you wouldn’t believe,” Smith said.
In fact, an early arrival in late April was a couple days old when the crew arrived, and they couldn’t catch it. Since then, however, the researchers have found 29 lambs, one of which was stillborn. Of the 28 lambs that were collared, only 14 are still alive. Smith has been packing up the carcasses and shipping them off to the laboratory, to confirm what he expects as the familiar cause of death.