Animal Diversity Web

Ge­o­graphic Range

Ovis canaden­sis is found in the Rocky Moun­tains from south­ern Canada to Col­orado, and as a desert sub­species (O. c. nel­soni) from Nevada and Cal­i­for­nia to west Texas and south into Mex­ico. (Festa-Bianchet, 1999)

• Biogeographic Regions
• nearctic
  • native

Habi­tat

Ovis canaden­sis canaden­sis in­hab­its alpine mead­ows, grassy moun­tain slopes and foothill coun­try in prox­im­ity to rugged, rocky cliffs and bluffs. Bighorn sheep re­quire drier slopes where the an­nual snow­fall is less than about sixty inches a year, since they can­not paw through deep snow to feed. The win­ter range usu­ally lies be­tween 2,500-5,000 feet in el­e­va­tion, while the sum­mer range is be­tween 6,000-8,500 feet. (Festa-Bianchet, 1999)

• Habitat Regions
• temperate
• terrestrial

• Terrestrial Biomes
• desert or dune
• chaparral
• mountains

• Range elevation

  800 to 2500 m

  2624.67 to 8202.10 ft

Phys­i­cal De­scrip­tion

Males 119-127kg; fe­males 53-91 kg. Rams typ­i­cally mea­sure 160-180 cm from head to tail, while ewes are ap­prox­i­mately 150 cm. Bighorn sheep have dou­ble-lay­ered skulls shored with struts of bone for bat­tle pro­tec­tion. They also have a broad, mas­sive ten­don link­ing skull and spine to help the head pivot and re­coil from blows. Horns may way as much as 14 kg, which is the weight of all the bones in a ram's body. The horns of a fe­male are much smaller and only slightly curved. The horns of a ram can tell much about him such as his age, health, and fight­ing his­tory. The desert sub­species, Ovis canaden­sis nel­soni, is some­what smaller and has flat­ter, wider-spread­ing horns. The pelage of Ovis canaden­sis is smooth and com­posed of an outer coat of brit­tle guard hairs and short, grey, crimped fleece un­der­fur. The sum­mer coat is a rich, glossy brown but it be­comes quite faded by late win­ter. (Festa-Bianchet, 1999)

• Other Physical Features
• endothermic
• homoiothermic
• bilateral symmetry

• Sexual Dimorphism
• male larger
• ornamentation

• Range mass

  53 to 127 kg

  116.74 to 279.74 lb

• Range length

  150 to 180 cm

  59.06 to 70.87 in

• Average basal metabolic rate

  114.674 W

  AnAge

Re­pro­duc­tion

Bighorn sheep are per­haps best known for the head-to-head com­bat be­tween males. Horn size is a sym­bol of rank, and the mass of the horns (as much as 14 kg) is used to a male's best ad­van­tage as he smashes into an op­po­nent at speeds of 20 miles per hour. Com­bat has been ob­served to last for as long as 25.5 hours (with ap­prox­i­mately 5 clashes an hour) until one of the males con­ceded. Males do not de­fend ter­ri­to­ries but rather en­gage in bat­tles over mat­ing ac­cess to a par­tic­u­lar fe­male. Male dom­i­nance sta­tus is de­ter­mined by age as well as horn size, and ho­mo­sex­ual ac­tiv­ity often oc­curs in groups of males with the dom­i­nant an­i­mal be­hav­ing like a court­ing male and the sub­or­di­nate play­ing the role of an es­trous fe­male. Ewes are sea­son­ally poly­oe­strous and will ac­cept sev­eral rams, often fre­quently, when in oestrus. Be­cause of in­tense com­pe­ti­tion be­tween males for fe­males and the dom­i­nance hi­er­ar­chy based on age and size (in­clud­ing the size of the horns), males do not usu­ally mate until they are seven years old. Younger males will mate sooner if dom­i­nant rams in their group are killed. (Festa-Bianchet, 1999)

• Mating System
• polygynous

Rut­ting sea­son is in the au­tumn and early win­ter, and births take place in the spring. Mat­ing for the desert bighorn, how­ever, can last from July to De­cem­ber. Ges­ta­tion lasts from 150-180 days, after which usu­ally one, rarely two, young are born. New­borns are pre­co­cial and are able to fol­low their moth­ers at a good pace over the rocky ter­rain after the first week. Within a few weeks of birth, off­spring form bands of their own, seek­ing out their moth­ers only to suckle oc­ca­sion­ally. They are com­pletely weaned by 4 to 6 months of age. Ovis canaden­sis fe­males have been mated when 10 to 11 months old in cap­tiv­ity, but they gen­er­ally do not breed until their sec­ond or third year in the wild. (Festa-Bianchet, 1999)

• Key Reproductive Features
• iteroparous
• seasonal breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual
• viviparous

• Breeding interval

  Bighorn sheep breed once yearly.

• Breeding season

  Mating occurs from July to December, with most activity concentrated in the fall rut.

• Range number of offspring

  1 to 2

• Average number of offspring

  1.36

• Average number of offspring

  1

  AnAge

• Range gestation period

  5 to 6 months

• Range weaning age

  4 to 6 months

• Range time to independence

  4 to 6 months

• Range age at sexual or reproductive maturity (female)

  1 (low) years

• Average age at sexual or reproductive maturity (female)

  2-3 years

• Range age at sexual or reproductive maturity (male)

  7 (high) years

Fe­male bighorn sheep seek out pro­tected areas to give birth to their lambs. They nurse the young for 4 to 5 months, with the lambs in­creas­ing from about 4 kg at birth to 25 to 35 kg at wean­ing (males gen­er­ally weigh­ing more). Lambs are ca­pa­ble of walk­ing and fol­low­ing their moth­ers on pre­cip­i­tous ter­rain soon after birth. Males do not par­tic­i­pate in parental care. (Festa-Bianchet, 1999)

• Parental Investment
• altricial
• pre-fertilization
  • provisioning
  • protecting
    • female
• pre-hatching/birth
  • provisioning
    • female
  • protecting
    • female
• pre-weaning/fledging
  • provisioning
    • female
• post-independence association with parents
• extended period of juvenile learning

Lifes­pan/Longevity

Longevity de­pends on pop­u­la­tion sta­tus. In de­clin­ing or sta­ble pop­u­la­tions, most sheep live over 10 years, with a max­i­mum of 19 years. How­ever in an ex­pand­ing pop­u­la­tion with heavy re­pro­duc­tion, av­er­age life span is only 6 to 7 years. Fe­males have been known to live up to 19 years and males to 14 but at­tain­ing these ages is rare. Even in areas where no hunt­ing oc­curs, fe­males rarely make it past 15 and males rarely live be­yond 12. Ju­ve­nile mor­tal­ity is vari­able and can be quite high, from 20 to 80%, av­er­ag­ing 5 to 30%. Be­tween the ages of 2 and 6 there is rel­a­tively low mor­tal­ity. (Festa-Bianchet, 1999)

• Range lifespan
  Status: wild

  19 (high) years

• Typical lifespan
  Status: wild

  6 to 15 years

Be­hav­ior

Al­though not as well built for climb­ing as moun­tain goats, bighorn sheep zigzag up and down cliff faces with amaz­ing ease. They use ledges only 2 inches wide for footholds, and bounce from ledge to ledge over spans as wide as 20 feet. They can move over level ground at 30 miles per hour and scram­ble up moun­tain slopes at 15 mph. They also swim freely, de­spite their mas­sive bulk and the weight of their horns.

Most pop­u­la­tions un­dergo sea­sonal move­ments, gen­er­ally using larger up­land areas in the sum­mer and con­cen­trat­ing in shel­tered val­leys dur­ing the win­ter.

Bighorn sheep are gre­gar­i­ous, some­times gath­er­ing in herds of over 100 in­di­vid­u­als, al­though small groups of 8 to 10 are more com­mon. Ma­ture males usu­ally stay apart from fe­males and young for most of the year in sep­a­rate bach­e­lor flocks. Young fe­males gen­er­ally re­main in their mother's group (led by an older ewe), but males de­part when two to four years old and join a group of rams. Young sheep of both sexes learn mi­gra­tory paths and suit­able habi­tats from adults in the group. (Festa-Bianchet, 1999)

• Key Behaviors
• cursorial
• terricolous
• diurnal
• motile
• migratory
• social
• dominance hierarchies

Home Range

Home ranges are quite large, av­er­ag­ing nearly 17 square km.

Com­mu­ni­ca­tion and Per­cep­tion

Bighorn sheep are very alert and have re­mark­able eye­sight that al­lows them to judge dis­tances ac­cu­rately in jump­ing and lo­cat­ing footholds. They often watch other an­i­mals mov­ing at dis­tances of up to a mile away. Bighorn sheep prob­a­bly also use chem­i­cal cues, as do most mam­mals, to dis­tin­guish re­pro­duc­tive states and may use vi­sual cues to as­sess dom­i­nance among males. Bighorn sheep are less vocal than do­mes­tic sheep. The lambs bleat, and ewes re­spond with a gut­teral "ba." At other times of the year, adults utter throaty rum­bles or "blow" in fright. Dur­ing the rut, the rams fre­quently snort loudly. (Festa-Bianchet, 1999)

• Communication Channels
• visual
• acoustic
• chemical

• Perception Channels
• visual
• tactile
• acoustic
• chemical

Food Habits

Bighorn sheep are mainly di­ur­nal, feed­ing in­ter­mit­tently through­out the day. Ovis canaden­sis canaden­sis is largely a grazer, con­sum­ing grasses, sedges, and forbs, but it will take some browse when pre­ferred food is scarce (es­pe­cially in win­ter). Desert bighorns (O. c. nel­soni) eat a va­ri­ety of desert plants and get most of their mois­ture from the veg­e­ta­tion, al­though they still visit water holes every sev­eral days. (Festa-Bianchet, 1999)

• Primary Diet
• herbivore
  • folivore

• Plant Foods
• leaves

Pre­da­tion

The avail­abil­ity of es­cape ter­ri­tory in the form of rocky cliffs is im­por­tant to bighorn sheep sur­vival. If a sheep can reach a rocky out­crop or cliff, it is usu­ally safe from the at­tack of wolves, coy­otes, bears, Canada lynx, and moun­tain lions. Golden ea­gles (Aquila chrysae­tos) may take some lambs. (Festa-Bianchet, 1999)

• Known Predators

  • wolves (Canis lupus)
  • coyotes (Canis latrans)
  • bears (Ursus)
  • Canada lynx (Lynx canadensis)
  • mountain lions (Puma concolor)
  • Golden eagles (Aquila chrysaetos)

Ecosys­tem Roles

Bighorn sheep are im­por­tant preda­tors of grasses and shrubs in their na­tive land­scapes, they are also im­por­tant sources of prey for large preda­tors. Bighorn sheep are hosts for a num­ber of par­a­sites. Ne­ma­tode lung­worms, Pro­to­strongy­lus stilesi and P. rushi, in­fect all bighorn sheep in­di­vid­u­als and prob­a­bly co-evolved with these sheep in North Amer­ica. Most sheep do not ex­pe­ri­ence any sig­nif­i­cant dele­te­ri­ous ef­fects of lung­worms. (Festa-Bianchet, 1999)

Eco­nomic Im­por­tance for Hu­mans: Pos­i­tive

Na­tive Amer­i­cans and early set­tlers prized bighorn meat as the most palat­able of Amer­i­can big-game species. Na­tive Amer­i­cans also used the horns to fash­ion large cer­e­mo­nial spoons and han­dles for uten­sils. The horns have also been pop­u­lar for many cen­turies as tro­phies. Bighorn sheep may serve as an at­trac­tion for eco­tourism ven­tures in parts of west­ern North Amer­ica. (Festa-Bianchet, 1999)

• Positive Impacts
• food
• body parts are source of valuable material
• ecotourism

Eco­nomic Im­por­tance for Hu­mans: Neg­a­tive

There are no known neg­a­tive ef­fects of bighorn sheep on hu­mans.

Con­ser­va­tion Sta­tus

Sev­eral pop­u­la­tions may be threat­ened with even­tual ex­tinc­tion, bighorn num­bers are only one-tenth the pop­u­la­tion that ex­isted when west­ern set­tlers first began ex­ploit­ing the Rock­ies. Their main threats are un­reg­u­lated or il­le­gal hunt­ing, in­tro­duced dis­eases, com­pe­ti­tion from live­stock, and con­tin­ual human en­croach­ment on their habi­tat. The sub­species O. c. auduboni of the Black Hills and ad­ja­cent areas has al­ready be­come ex­tinct. Bighorn sheep are in­com­pat­i­ble with do­mes­tic sheep be­cause they are sus­cep­ti­ble to dis­eases of do­mes­tic live­stock, in­clud­ing pneu­mo­nia, which is pe­ri­od­i­cally re­spon­si­ble for large die-offs in bighorn sheep pop­u­la­tions. Hunt­ing has been pro­hib­ited or con­trolled since the early 1900's, but much il­le­gal poach­ing still oc­curs. Hunt­ing for tro­phies is par­tic­u­larly dam­ag­ing to the co­he­sive­ness of bighorn groups be­cause it elim­i­nates the dom­i­nant, breed­ing males. Re­cov­ery of num­bers has been slow for these an­i­mals and their fu­ture is threat­ened un­less fur­ther con­ser­va­tion mea­sures are im­ple­mented. Cal­i­for­nia bighorn sheep (O. c. cal­i­for­ni­cus) are con­sid­ered en­dan­gered under the U.S. En­dan­gered Species Act. (Festa-Bianchet, 1999)

• IUCN Red List

  Least Concern
  More information

• IUCN Red List

  Least Concern
  More information

• US Federal List

  Endangered

• CITES

  Appendix II No special status

Con­trib­u­tors

Tanya Dewey (au­thor), An­i­mal Di­ver­sity Web.

Liz Bal­lenger (au­thor), Uni­ver­sity of Michi­gan-Ann Arbor.

Ref­er­ences

Ban­field, A.W.F. 1974. The Mam­mals of Canada. Uni­ver­sity of Toronto Press, Toronto.

Darym­ple, B.W. 1985. North Amer­i­can Big-Game An­i­mals. Out­door Life Books, New York.

Geist, V. 1979. Hoofed mam­mals. In: Wild An­i­mals of North Amer­ica. Na­tional Ge­o­graphic So­ci­ety, Wash­ing­ton, D.C.

Nowak, R.M. and J.L Par­adiso. 1983. Walker's Mam­mals of the World. 4th edi­tion. John Hop­kins Uni­ver­sity Press, Bal­ti­more, MD.

Festa-Bianchet, M. 1999. Bighorn sheep. Pp. 348-350 in D Wil­son, S Ruff, eds. The Smith­son­ian Book of North Amer­i­can Mam­mals. Wash­ing­ton, D.C.: The Smith­son­ian In­sti­tu­tion Press.