Nevada’s sheep rebound from disease

The bighorn sheep hunting season looks optimistic after herd populations rebounded from a disease outbreak several years ago.

The bighorn sheep hunting season looks optimistic after herd populations rebounded from a disease outbreak several years ago.

A large increase occurred in desert bighorn ram tags in 2012. Several herds had been underestimated for the last few years along with building mature ram age classes.

Unlike mule deer, bighorn ram harvest is based on recruitment of yearling rams 5 to 9 years ago. The statewide goal of average ram harvest age is 6 years old. Large fluctuations in lamb recruitment from year to year cause both weak and strong age classes to occur over time. So if 5-9 years ago, yearling ram recruitment was weak, quotas will be lowered accordingly, but if past recruitment of young rams was strong and verified by current survey data, quotas will be raised to accommodate the availability of mature rams.

The Nevada Department of Wildlife issued 281 tags in 2012, an increase of 59 tags from 2011. Hunter success continued to be strong at 86 percent compared to 87 percent in 2011. Hunters averaged 5.7 days in the field compared to the 20-year average of 6.2 days.

The 2012 statewide average age of harvested rams was 6.5 years compared to the 20-year average of 6.3. The statewide average unofficial B&C score was 154 points, the second highest average score in 20 years.

The statewide desert bighorn survey in 2012 classified a large number of bighorn at just over 4,000. Unfortunately, a significant drop in lamb recruitment was documented from 41 lambs:100 ewes in 2011 to a ratio of 29 lambs in 2012.

Though several mountain ranges experienced late-summer monsoonal rains, it was too late to reverse 6 months of very poor moisture from November through May, the critical months of pregnancy, forage plant germination and green up, birthing, and weaning. But even with low fawn recruitment, the statewide desert bighorn population estimate again rose to almost 9,000 adults.

The bighorn restoration program activity this past season was reduced from the all time high number in 2011 of desert bighorn transplanted in Nevada. To reduce wildlife/human conflicts in Boulder City, 18 rams were captured from Hemenway Park and relocated to the Virginia and Excelsior Ranges where ewe/lamb translocations had occurred in 2011.

Water development work continues to be a critical component of Nevada’s bighorn management program. Since 2011, there have been 6 upgrades (tanks and apron), 6 rebuilds, 3 major repairs, and 9 new guzzlers constructed for desert bighorn sheep. The majority of the new guzzlers were built in western and central Nevada where opportunities still exist to expand existing herds and for reintroduction of new herds.

Every year, it becomes more and more challenging to manage the many desert bighorn herds “at risk” to domestic/exotic sheep and goat interaction and irresponsible domestic sheep operators allowing stray animals where deadly virulent pathogens may be transmitted to wild sheep; plan and implement captures and transplants involving wilderness areas; control dozens of herds that have serious seasonal carry capacity issues with insufficient viable release sites; succeed in reducing excessive feral horse and burro numbers that destroy fragile desert habitats; and minimize long-term impacts to bighorn habitat by energy and infrastructure development.


During the 2012 California bighorn season a total of 59 tags were issued including five nonresident tags, one Heritage tag and one Dream tag. Information gathered from the mandatory check out of harvested bighorn indicates that 53 of the 59 tag holders were successful in taking a ram. The average age of all harvested rams was seven years with an average Boone and Crockett score of 149 inches.

Biologist’s classified 1,023 California bighorn sheep this past year with a ratio of 46 rams: 100 ewes: 42 lambs. The total number of sheep observed during these surveys increased slightly from the previous year and this sample of bighorn represents the highest total ever recorded during these surveys. Both the observed lamb and ram ratios declined slightly from what was observed during 2011 surveys but they remain within acceptable limits.

The statewide California bighorn population is estimated at 2,100 sheep, which is an increase of 5 percent over last year. Generally, Nevada’s California bighorn populations continue to do well.

Capture and transplanting efforts this past year targeted high density bighorn herd in the Pine Forest, Black Rock and Sheep Creek Mountain Ranges. A total of 78 bighorn were removed from these 3 ranges and released into the Jackson, Hays Canyon and Santa Rosa Ranges. The Hays Canyon Range was a reintroduction after the 100 percent pneumonia dieoff of the bighorn herd that occurred in 2007.


A total of eight Rocky Mountain bighorn sheep tags were issued in 2012, an increase from 2011 with Unit 091 back on line with two tags and one tag increase in Unit 074. Seven of the eight hunters were successful. The average age of 7.0 was slightly less than the long-term average of 7.2. The average B&C green-score was 158, much lower than the long-term average but to be expected without ram harvest from Units 101 or 102.

Helicopter surveys were conducted in units 074, 091, 114, and 115. A total of 124 bighorns was classified yielding ratios of 59 rams:100 ewes:24 lambs. The low average lamb ratio was primarily due to the Pilot Peak/Leppy Hills herd in Unit 091 that only had 4 lambs:100 ewes, which is to be expected based on past and recent association with domestic sheep that trail within a few miles of the herd and the pneumonia event that occurred in 2010.

The statewide 2012 Rocky Mountain bighorn sheep population is estimated to be 260 sheep, which is up from last year’s estimate. The 2009 statewide estimate was approximately 550 Rocky Mountain bighorns.

Disease events in 2010 decimated the bighorn populations in Unit 101 and Unit 102 (over 90 percent confirmed losses in each herd) and all but eliminated lamb recruitment in Unit 091. Similar to what was seen during past disease events, it is anticipated poor lamb recruitment in Units 091 and 102 will likely be realized in the next several years thus suppressing population growth.

The Nevada Department of Wildlife will continue to conduct monitoring efforts in an attempt to identify causal agents or catalysts that may have been involved.

Unit 101 was depopulated in February 2012 through an aerial capture operation in which 10 ewes and one lamb were captured from Unit 101 and released into Unit 102. Four rams were also taken from this unit and transported to the Washington State University’s bighorn disease research facility in Pullman.

After 3 years of planning, preparation, and removing all surviving bighorn from the East Humboldts, the day finally came to reintroduce bighorn sheep to the mountain. A small group of NDOW biologists, wildlife veterinarian, and sportsmen volunteers travelled to Alberta, Canada in early February 2013.

NDOW will share one tag in Unit 091 in 2013 with the state of Utah as per our cooperative agreement with their Division of Wildlife Resources in co-managing this interstate herd.


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