Area Bighorn Sheep on the Move
By Larry Hyslop

Captured bighorn sheep removed from the East Humboldt Range

One of my favorite summer activities is camping at Angel Lake and a favorite camping activity is glassing the slopes for bighorn sheep but not this year. There are no bighorn sheep in the East Humboldt Range as the Nevada Department of Wildlife (NDOW) has removed the few known survivors of a recent die-off.

Caleb McAdoo is the local NDOW game biologist for this area. He described the history of bighorns in the East Humboldts. Native sheep were extirpated from the range in the early 1900s. In 1992, 31 Rocky Mountain bighorns were placed in the Eastern Humboldt Range. By 2009, this population had increased to almost 200 animals. Unfortunately, during the winter of 2009-2010, a pneumonia-causing infection caused a die-off reducing the population to as few as 15 animals.

This winter, Native Range Helicopter Services used an aerial net gunning technique to capture the survivors. Ten ewes and one incredibly important lamb were released in Lamoille Canyon near the Lion’s Camp. Four rams were transported to Washington State University to be used in significant research studying this baffling disease.

NDOW’s plan for next winter is to bring in at least 20 bighorn sheep, mostly ewes, to restock the East Humboldts. These animals will likely come from Alberta, Canada, which supplied the original sheep placed in these mountains.

The history of bighorns in the Northern Ruby Mountains is much the same story. In 1987 and 1988, 45 bighorn sheep were placed in the Rubies. By 1995, this herd had grown to 160 animals when a die-off reduced the herd to almost 35 sheep. By 2009, the herd had grown back to 180 sheep but the most recent die-off left as few as 16 sheep.

Bighorn die-offs occur across the West and everyone is scrambling to figure out how best to handle them. It was NDOW’s decision to remove all animals exposed to the disease from the East Humboldts.

Bighorn rams love to roam long distances and it is likely if moved to the Rubies, they would have returned to the East Humboldts. The ewes and lamb are more likely to stay in the Rubies. Necropsies on sheep killed during the latest die-off in the Rubies, along with blood samples from captured survivors show the pathogens in both herds are the same so moving the ewes and lamb to the Rubies should not cause any worse complications.

One of many problems with these pneumonia-causing pathogens is that they stick around after a die-off. Lamb survival can remain low for several years, requiring either a longer recovery or no recovery. Lambs are produced and thrive while suckling, but after weaning they no longer receive antibodies from the ewe and often die of the infection. This is why the one recruited lamb in the East Humboldts is so important. Its survival shows other lambs may also survive and the herd could begin its recovery sooner than expected.

The die-off may have also killed at least 30% of the mountain goats. Getting an accurate count is very difficult, but it is evident far fewer kids were produced last spring. Since the infection also causes lower kid recruitment, it will require a few years to determine the actual loss.

“This action is being looked at by every Western state who manages sheep,” Caleb said. As wildlife managers struggle to deal with their own die-offs, they will want to see how NDOW’s strategy might be applied to their state efforts.

Elko Daily Free Press, “Nature Notes”, 3/8/2012
© Gray Jay Press, Elko, NV

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