Q. What are the names for male and female bighorn and how can you tell them apart?
A. Male bighorn sheep or "rams" are easily identified by their large spiral horns which grow throughout their lives. An adult ram's horns may measure over 30 inches each in length and reach 15 inches in circumference at the base. Female bighorn or "ewes" have slender, straighter horns that grow throughout their lives to lengths of 8-10" for Rocky Mountain bighorn ewes and 12-17" for desert bighorn ewes. Young bighorn that are less than 1 year of age are referred to as lambs.
Q: What are some of the problems affecting bighorn sheep?
A. At the beginning of the nineteenth century, bighorn sheep in North America were estimated to number between 1.5 and 2 million, but today less than 70,000 remain. In the late 1800's, hunting, competition from livestock grazing, and diseases introduced by domestic livestock devastated bighorn populations. Although problems with domestic livestock are subsiding, they still exist and are now accompanied by accelerating habitat loss and human disturbance. Habitat loss and fragmentation are recognized as the most significant threats facing bighorn sheep today. Natural predation from mountain lions, coyotes and bobcats also pose a risk to bighorn populations that have dwindled to low numbers.
Q. Have any bighorn sheep populations gone extinct?
A. An entire subspecies of bighorn sheep, the Audubon bighorn, which inhabited parts of Montana, North Dakota, South Dakota, Wyoming and Nebraska was extirpated by 1925. At various times in the early 1900's, bighorn sheep were extirpated from the states of Washington, Oregon, Texas, North Dakota, South Dakota, Nebraska, and the Mexican states of Chihuahua and Coahuila. Fortunately, many populations have been re-established through transplanting bighorn sheep from healthy populations to vacant habitat.
Q. What is the life span of a bighorn sheep?
A. Rams typically live 9-12 years, while ewes usually live 10-14 years.
Q. How much do bighorn sheep weigh?
A. Adult desert bighorn rams weigh between 150-200 pounds and ewes weigh between 100-125 pounds. Adult Rocky Mountain bighorn rams are heavier, weighing from 160-250 pounds, and occasionally obtaining 300 pounds. Rocky Mountain bighorn ewes typically weigh 115-200 pounds.
Q. What do bighorn sheep eat?
A. Although the diet of bighorn sheep varies according to the habitat and season, bighorn primarily eat grasses, shrubs, and forbs. Some favorite shrubs for desert bighorn sheep are acacia or catclaw, encelia, sweetbush, and krameria. Generally, bighorn sheep are opportunistic feeders that adapt their diet to the forage available.
Q. What are the natural predators of bighorn sheep?
A. Mountain lions, wolves, bobcats, coyotes and golden eagles are predators of bighorn sheep. Eagles have been known to prey upon lambs, but they are unable to kill adult bighorn. Predation is usually not a problem for healthy bighorn populations; however, when bighorn are supressed by other factors, predation can limit recovery and potentially drive a population to extinction.
Q. When is the breeding season for bighorn sheep?
A. The breeding season, or rut, generally extends from August-November for desert bighorn sheep and October-January for Rocky Mountain and California bighorn sheep. It is during this time that rams clash heads to fight for dominance. In each band of rams there is a dominance order, and the higher ranking rams do most of the breeding. Genetic studies are currently underway to determine the percentage of breeding completed by dominant and subordinate rams. Bighorn sheep have an approximately 6 month gestation period and most ewes give birth to one lamb per year.
Q. When is the lambing season?
A. Lambing seasons vary by location and year. Desert bighorn lambs are usually born in January-June, with the majority of births in February-April. The lambing season for bighorn sheep in colder climates is more concentrated and most births occur in April-June. Prior to giving birth, adult ewes isolate themselves in steep rocky areas. Newborn lambs weigh 8-10 pounds and can walk within hours after birth, however they are dependant upon steep terrain for protection from predators. Lambs follow their mothers for the first year of life to learn their home range and behavior.
Recommended books regarding mountain sheep:
Sheep on the Brink - A History of the Bighorn Institute. 2019. Mike Rivkin and Roland Burbank. Silverfish Press, Avalon, California, 63 pgs.
The Desert Bighorn - Its Life History, Ecology, and Management. 1980. Edited by G. Monson and L. Sumner. The University of Arizona Press, Tucson, Arizona. 370 pgs.
The Wild Sheep of the World. 1982. Edited by R. Valdez. Wild Sheep and Goat International, Mesilla, New Mexico. 186 pgs.
Return of Royalty. 1999. Edited by D. E. Toweill and V. Geist. Boone & Crockette Club and the Foundation for North American Wild Sheep, Missoula, Montana. 214 pages.
Mountain sheep of North America. 1999. Edited by R. Valdez and P. Krausman. Univeristy of Arizona Press, Tucson, Arizona. 353 pages.
Desert Bighorn Sheep: Wilderness Icon. 2014. Mark Jorgensen and Jeff Young. Sunbelt Publications. 143 pgs.