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Dreadful news for bighorns

Disease takes toll at Yakima River Canyon

A bighorn ewe looks over her newborn lamb, which was killed by coyotes soon after this photo was taken. (Gordon King)
A bighorn ewe looks over her newborn lamb, which was killed by coyotes soon after this photo was taken. (Gordon King)
Scott Sandsberry Yakima Herald-Republic

SELAH, Wash. – They looked like they were flying.

Against the Yakima River Canyon’s backdrop of rock promontories and steep scree slopes, two coyotes chased a bighorn lamb in a pursuit that was both high drama and inevitably brief.

Once the lamb bolted from the relative safety of the high rocks in its frantic attempt to escape, it became easy prey for the swifter, longer-legged predators.

But while its death is a reminder of the daily dangers facing wildlife, another far more prolific and efficient killer – pneumonia – is wiping out the youngest members of the bighorns that populate the canyon walls west of the Yakima River.

Five years ago, a pneumonia outbreak among the canyon bighorn herd prompted state wildlife biologists to make the gut-wrenching decision to kill dozens of sick bighorns in hopes of preventing the disease from spreading to nearby herds.

Since then, each spring’s new lambs have been dying in droves.

And the pace seems to be picking up. Last year, lamb mortality spiked in summer, when the lambs were 2 to 3 months old. This year, the disease is hitting lambs that aren’t yet 3 weeks old.

“We figure, based on the (herd’s) population and pregnancy rates, we probably had 150, 160 lambs hit the ground this lambing season,” said Jeff Bernatowicz, a biologist with the state Department of Fish and Wildlife. “If we have 50 to 60 survive, we’ll be jumping up and down. We’d be ecstatic.

“But with this pneumonia, we’re probably going to have 10 or 15 instead.”

Volunteers, many of them from Safari Club International chapters around the state, have been observing the canyon bighorns through spotting scopes, both to monitor the disease’s progress and to help state biologists beat scavengers to the bodies.

The freshest of carcasses are sent to Washington State University’s veterinary diagnostic lab to analyze whether the cause is the same mycoplasma associated with the 2009 and 2010 canyon bighorn deaths.

“It’s a very typical pattern,” said Kristin Mansfield, a veterinarian with the wildlife department. “When disease enters the bighorn population, typically it kills many adults the first year and thereafter it primarily affects the lambs – and it can go on for years.

“It has gone on for years in Hells Canyon (along the Snake River between Washington, Oregon and Idaho) to the point where we’re not getting any recruitment (next-generation survival) because the lambs aren’t making it to adulthood.”

Like the initial Hells Canyon die-offs in 1995 and 1996, the Yakima disease outbreaks are believed to have been caused by bighorn interaction with domestic sheep or goats, which carry the bacteria but are not susceptible to it.

No such domestic livestock are grazed anywhere near the Yakima River Canyon bighorns, but young bighorn rams will travel long distances during the rutting season in search of prospective mates.

If they come into contact with domestic sheep or goats, they can carry the disease back to the herd, where the effects can be wide-ranging and long-lasting. Some bighorn populations around Hells Canyon are two-thirds what they were prior to 1995, others are much worse.

When an adult bighorn survives the first die-off it may be less susceptible to ensuing outbreaks, but the high lamb mortality may ultimately doom the herd, said Frances Cassirer, an Idaho Fish and Game Department research biologist who oversees the Hells Canyon bighorn sheep restoration project.

“It’s what we call ‘extinction debt’ – where things get worse over time,” Cassirer said. “The adults are surviving, but they’re also aging.”

Wildlife experts have no answer on how to protect the bighorns from the deadly disease.

“We haven’t figured out anything yet,” Cassirer said. “We’re not giving up, but … right now, there’s no cure.”

Nor is there much hope for Yakima River Canyon bighorns as the pneumonia moves through the herd’s youngest members.

“You can actually see their chests heaving, shaking their heads and coughing,” Joe Greenhaw, a volunteer from SCI’s Seattle Puget Sound chapter, said as he watched bighorns through binoculars from alongside State Route 821 in the canyon.

Greenhaw has also seen lambs tumble to the canyon floor, too weak to follow their mothers along the steep basalt face.

One ewe spent most of Thursday bleating mournfully after the death of its lamb, going back and forth between the lamb’s body and the rock outcropping above. On Friday morning, it continued to visit what little was left of the lamb, even after the scavengers – magpies, crows and golden eagles, perhaps even coyotes – had their fill.

If last year’s die-off was any indication, this next month will be a grisly death watch for the volunteers.

“Below Roza Dam, we had right at 85 ewes, and I’m sure 95 percent of them had lambs, so we probably had 75 or 85 lambs at the middle of May,” Greenhaw said. “By the middle of the September count, we had two lambs left.”

As Greenhaw and fellow volunteer Mike Price scanned the Yakima River Canyon slopes on a recent Friday morning, they saw numerous ewes that were alone, their lambs nowhere to be seen.

The observers took momentary comfort in seeing a cluster of bighorns with apparently healthy lambs.

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