This tiny parasite is causing big problems for bighorns

The steep cliffs and drainages near Hells Canyon on the Oregon-Idaho border make perfect places for bighorn ewes to birth lambs.

To have the lambs, the sheep separate themselves from the herd, partly to avoid predators for the first few days of the lamb’s life, said Katey Huggler, a doctoral student at the University of Idaho.

Huggler would travel daily to monitor these ewes as they gave birth. It’s important to catch and collar the lambs a day or two after they’re born or else the lambs are too fast, she said.

That’s how Huggler started noticing stillborn lambs, two in 2021 and another in 2022, a relatively high number of stillborn lambs for this small bighorn sheep herd.

“It’s kind of a hit when we lose a lamb, especially in such a small population,” Huggler said.

In 2011, the Asotin Creek herd first got hit by a bout of pneumonia, a highly contagious bacteria that can persist in herds for decades, decimating populations. The following die-off cut the herd's numbers nearly in half. The population has remained stagnant since at about 55 sheep, Huggler said.

“We really want this population to go back to what it used to be, which means we have to have lambs,” Huggler said. “So it’s kind of a huge bummer when you see that mom had worked so hard to grow this pretty normal sized lamb, and then it ended up just being dead.”