Date: 09/08/05
Contact: Lynne Foster
Phone: (775) 688-1997

Results of Desert Bighorn Sheep Tests Inconclusive

Extensive testing has proven inconclusive as to the cause of death of 22 desert bighorn sheep in southern Nevada, reports Dr. Dan Crowell, D.V.M., a state veterinarian with the Nevada Department of Agriculture. The sheep were discovered by ATV riders on July 24, 2005 near a water development in the McCullough Range south of Las Vegas.

“We did all the testing we reasonably could, for 13 different factors including diseases, metals, bacteria, poisons and toxins,” Crowell said in a report released August 31. Nevada Department of Wildlife requested assistance from the both the state veterinarian’s office and other expert wildlife pathologists to identify the cause of death.

Three factors were not ruled out: blue-green algae, dehydration, and botulism, or some combination of the three.

“Although water samples were negative for the toxins associated with blue-green algae and botulism toxicity, it is possible that the toxins could have been present and were subsequently flushed from the system with the rain incident,” stated Crowell. A storm on Saturday evening continuing into Sunday morning, when the sheep were found, caused high rainfall and numerous lighting strikes. Early suspicions were that lightning might have been a factor in the animal deaths. However, body decomposition of the animals showed that they had died at least 24 to 48 hours prior to the Sunday morning lightning storm. Researchers could find no reports of lightning strikes in the area for the previous week. There was no

observable evidence of lightning on the carcasses, or in the environment. In addition, some of the animals were as far as 200 yards apart.

The animals were found near a water development. Wildlife, including desert bighorn sheep, access the stored water via a “drinker.” Biologists said that the drinker could have been dry prior to the rain. It appeared that critically high daytime temperatures that neared 120 degrees may have been a factor in the die-off, although tests for elevated sodium in brain tissue indicative of dehydration also proved inconclusive.

“We have read reports of similar cases in Arizona and California that showed animals occasionally die near dry water sources, even with other water sources available within reasonable distances” said Mike Cox, the big game staff biologist for NDOW. “It may seem strange, that they would stay near a dry water source, when they could have traveled to the next available source approximately five miles away.”

The dead animals showed no signs of trauma, such as being shot.

Other causes of death that were ruled out included anthrax, heavy metals, toxicity, antifreeze, strychnine, respiratory viruses, fertilizer-type chemicals, and compound 1080 (used in predator control).

In the 1990s the bighorn sheep population in the area was estimated at about 130 animals. Through the addition of water developments and favorable conditions the population has increased to an estimated 320 wild sheep.

At least two sportsmen’s groups and a number of volunteers assisted the Nevada

Department of Wildlife on the investigation. Nevada Bighorns Unlimited – Reno paid the expensive laboratory costs, and Fraternity of the Desert Bighorn paid for an aerial survey and supported work on the ground. “We appreciate all the assistance that we received on this,” said Doug Hunt, NDOW Deputy Director, “ and we only wish it could have ended more conclusively.”

Desert bighorn sheep are Nevada’s state animal. More than 5,400 desert bighorns are found in mountain ranges in the southern, western, and central part of the state.

The Nevada Department of Wildlife is the state agency responsible for the protection, restoration and management of fish and wildlife resources, and the promotion of boating safety on Nevada’s waters. Wildlife offices are located in Las Vegas, Henderson, Winnemucca, Fallon, Elko, and Reno. For more information, contact the agency web site at www.ndow.org.

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