LAS VEGAS (KLAS) — A study of bighorn sheep in Death Valley National Park aims to figure out why some herds are more resistant to disease than others.

Sixty sheep were captured and transported by helicopter as part of the study. Researchers collected genetic, disease, immune and microbiome samples from each bighorn sheep, and they were released after a GPS collar was attached for tracking.

A bighorn sheep is transported by helicopter as part of a study in Death Valley National Park. (Photo courtesy NPS/Bill Sloan)

“In November and early December, park visitors might have seen bighorn sheep hanging from a helicopter,” according to a park news release. “These GPS collars will help produce the most accurate picture of the location, movement, and size of desert bighorn herds in Death Valley to date. They will also provide real time monitoring of how bighorn sheep respond to challenges like disease, human activities and climate change.”

The study involves researchers at Oregon State University in cooperation with the National Park Service and the California Department of Fish and Wildlife.

“Diseases pose one the largest threats to the survival of desert bighorn sheep (Ovis canadensis nelsoni). Bighorn sheep were exposed to new diseases when domestic sheep and goats were brought into the West. Some diseases are common and relatively minor in domestic sheep and goats, yet can be deadly for bighorn sheep,” according to NPS.

National Park Service and Oregon State University biologists work with a bighorn sheep in November. (Photo courtesy California Department of Fish and Wildlife)

A survey of desert bighorns at the Nevada National Wildlife Refuge last year found that the population of herds there had declined dramatically.

Studies have shown that most desert bighorn sheep spend their lifetimes within a single mountain range, but some ewes and rams journey between mountain ranges. “These wanderers create important genetic diversity, but they can also spread disease between herds,” NPS said.

“While some herds interact with many wandering sheep, other herds are more isolated. Researchers at Oregon State University think that difference affects how bighorn sheep immune systems evolved. This could explain why some herds are more resistant to certain diseases,” NPS said.