Bovidae Author Don E. Wilson Author Russell A. Mittermeier text 2011 2011-08-31 Lynx Edicions Barcelona Handbook of the Mammals of the World – Volume 2 Hoofed Mammals 444 779 book chapter 58516 10.5281/zenodo.6512484 67b52095-db4b-43f8-a661-4aced0511111 978-84-96553-77-4 6512484 206. Bighorn Sheep Ovis canadensis French: Mouflon d’Amérique / German: Dickhornschaf / Spanish: Carnero de las Rocosas Other common names: Mountain Sheep; Audubon Bighorn (auduboni) , California Bighorn (californiana) , Desert Bighorn Sheep (mexicana , nelsoni , weemsi) Taxonomy. Ovis canadensis Shaw, 1804 , Alberta , Canada . Subspecies boundaries and number of taxa need clarification. Bighorn and Dall’s Sheep ( O. dalli ) probably hybridized prior to glacial maxima and during late Pleistocene in ice-free refugia. “Audubon Bighorn” (auduboni), consisting of extirpated populations from the Badlands of North and South Dakota , north-western Nebraska , eastern Wyoming , and Montana , is a synonym of the nominate subspecies canadensis . Populations of “ California Bighorn” (californiana) have been synonymized with canadensis or nelsoni and populations formerly assigned to californiana in the central and southern Sierra Nevada of California have been assigned to sierrae. Formerly recognized subspecies cremnobates, occurring in extreme southern California and northern Baja California , is a synonym of nelson. Five subspecies recognized. Subspecies and Distribution. O.c.canadensisShaw,1804—SWCanada(SBritishColumbia&SWAlberta),WUSA(Washington,Montana,Wyoming,NIdaho,NorthDakota,SouthDakota,NWNebraska,WColorado&NNewMexico). O.c.mexicanaMerriam,1901—SWUSA(SWArizona&SWNewMexico),NWMexico(NWSonora).ReestablishedinCoahuilaandChihuahua,Mexico. O.c.nelsoniMerriam,1897—NWUSA(Oregon,SWIdaho,Nevada,NECaliforniatotheGreatBasinDesertinUtah,SCalifornia&SArizona)andNWMexico(NBajaCalifornia). O.c.sierraeGrinnell,1912—California(C&SSierraNevada). O. c. weemsi Goldman, 1937 — S Baja California , Mexico . Descriptive notes. Head-body 109-169 cm (males) and 96-126 cm (females), tail 10.2-15. 2 cm (males) and 10.2-12. 7 cm (females), shoulder height 81-112 cm (males) and 76-91 cm (females), hindfoot 35.5-48. 3 cm (males) and 27.9-43. 2 cm (females); weight means 79 kg (up to 145 kg ) for males and 59 kg (up to 104 kg ) for females. Horn length means 90 cm (up to 126 cm ) for males and 26-2 cm (females), horn circumference means 37-3 cm (up to 44 cm ) for males and 12-8 cm (females). The longer, more massive curling horns of males clearly differentiate males and females; the mass of male skulls with horns minus lower jaw can exceed 20 kg . Males can be up to 70% larger than females. Body color is pale brown to dark chocolate, including the tail. There is a distinct white rump patch that extends to the side of the rump and above the base of the tail; the muzzle, usually the posterior of the legs, and the belly are white. The white of the hindlegs is continuous with the white rump patch. There usually is a blackish-brown mid-dorsal stripe extending to the tip of the tail. There is no neck ruff. The diploid chromosome numberis 54. Habitat. Steep, rugged terrain used for escape or security cover is a major habitat component, especially for ewes with lambs. Habitats include rough to gentle slopes in mountains and foothills, talus cliffs, rock outcrops, mesa tops, and canyons and adjacent river benches. Bighorn Sheep are found at elevations from below sea level in Death Valley, California , to above 3500 m . Daily temperatures can vary from —40°C in northern regions and higher elevations to greater than 40°C in desert habitats. These habitats encompass a variety of plant communities, including grasslands, alpine and subalpine meadows, riparian zones, shrub-steppes, desert, clear-cut or burned tall vegetation, and deciduous and conifer forests. Bighorn Sheep usually avoid areas with tall vegetation that obstructs their vision. Northern populations require grazing areas devoid of deep snow, such as wind-blown sites. In desert areas, water availability is an important factor, but sheep can survive without standing water for long periods. Major predators include Coyotes (Canis latrans), Gray Wolves (C. lupus), Pumas (Puma concolor ), and occasionally smaller carnivores and golden eagles (Aquila chrysaetos). Puma predation by individuals that concentrate on sheep can depress population growth in some Instances. Food and Feeding. Diets are highly variable due to the wide geographic landscape and habitat variability, seasonal availability of forage species, and potential age and gender forage preference differences. Forbs and grasses are the component of most sheep diets, but shrubs can dominate diets. In desert areas, shrubs can comprise more than 90% of summer diets. Water and seasonal precipitation have important effects on forage availability, quality, and palatability, especially in desert environments, and largely determine diet composition. Mineral licks are important sources of sodium, phosphorus, calcium, and probably trace minerals. Breeding. Ewes are monestrous; males are serially polygynous. Dominance among rams is established by ritualized head and body displays and by physical interactions, including horn clashes and head butting. Dominant, larger bodied, longer-horned rams guard a single estrous ewe from other rams. Males are sexually mature by 1-5 years, but usually they are prevented from participating in the rut by older rams. However, subdominant rams can father offspring and several males can mate with the same female. Ewes usually first mate when 2-5 years old and first give birth when three years old. Males older than five years do most of the breeding. In northern populations, mating occurs in late November and early December. After a gestation period of 170-180 days, ewes give birth to a single offspring; twins are rare. Social rank in ewes is not correlated with reproductive success, but high-quality females, those in a high nutritional plane, have a consistently higher probability of reproduction. Lamb survival is greater in ewes aged 4-12 years than for ewes aged two or three years. In northern populations, parturition coincides with warmer temperatures and the growth of spring vegetation in late May and early June. In desert environments, the mating season is prolonged; births occur from January through June, probably due to unpredictable precipitation patterns, although there is usually a peak period in births. However, the peak birth period coincides with a predictable timing of the winter-spring forage growing season, indicating that most desert sheep births also coincide with the period of nutrient availability. Ewes give birth in rugged,steep terrain in seclusion. Lambs weigh 2:7.4-5 kg at birth. After one to three days, when the lamb is able to follow the mother, theyjoin a ewe herd. Lamb and yearling mortality is highly variable, 20-80% for lambs and 5-30% for yearlings, and can exceed 90% during disease outbreaks, exceptionally cold, wet weather, or droughts. Coyotes and Bobcats (Lynx rufus ) are important predators of lambs. Lactating ewes are more vigilant about predators than non-lactating ewes. Activity patterns. During warm weather, feeding activities are concentrated at dusk and dawn. During winter, feeding periods increase, probably influenced by the shortened daylight hours and the poorer nutritional quality and availability of forage plants, especially in deserts and northern areas with snow cover. In deserts, feeding activity is curtailed by high summer temperatures during the day. Females, because of their added nutritional demands during pregnancy and after lambing, can spend proportionately more time feeding than males. Smaller rams spend more time foraging than larger rams. Movements, Home range and Social organization. Northern Bighorn Sheep usually migrate seasonally between winter and summer home ranges, which can involve movements of 10-20 km. Female herds show high home range fidelity. Elevational migrations are evident in northern populations in relation to plant phenology and to avoid areas of snow accumulation. Desert population movements are related to seasonal water and forage availability. Males tend to make longer movements and have much larger home ranges than females, especially during the mating season. They can move 50-60 km and encompass several mountain ranges. In the pre-Columbian period, when human structures were not a hindrance, desert populations were not sedentary, and the sheep crossed lower-elevation intermountain regions to move between mountain ranges. In Utah , the mean home range size for males was 61 km ?; for females it was 24 km ®. In arid areas, large female home ranges were correlated with widely scattered water sources; during the rainy season, home ranges and movements can increase because of greater availability of watering sources. However, in western Arizona , home ranges decreased with increasing precipitation indicating that forage quality was related to home range area. Bighorn Sheep aggregate in herds, which increases feeding efficiency and predator avoidance. Herd size, which can vary from two to over 100 individuals, is dependent on population size, habitat availability, season, and gender. During an extended period of the year, males form separate groups from females and occupy separate seasonal home ranges, but there can be spatial and temporal overlap. Female or maternal herds are composed of adult females, subadult females, lambs, and juvenile males. Young males leave female herds when they are old enough to dominate females, as 2-3year-olds. Subadult males tend to rejoin female herds in summer. Young females remain within their maternal herds throughout their life. Females select for areas with higher security cover (steep, rugged terrain) to maximize lamb survival, even though these areas can have lower forage quality; males select for higher forage quality or quantity to maximize body condition, at the risk of higher predation vulnerability. Mature males join ewe herds during the mating season, which increases herd size and probably stimulates sexual behavior and synchronizes estrous among females. Single males may be more evident during the mating period because of their movements in search of estrous ewes. Males form dominance hierarchies, with older, larger males dominant over younger, smaller males. Dominance is correlated with reproductive fitness. Older, physically and socially mature males do most of the mating, but in some populations, subadult rams can sire equal numbers of lambs. Although females can live up to 19 years and males up to 14 years, few females live beyond 15 years and males rarely live beyond twelve years in the wild. Status and Conservation. CITES Appendix II (populations in Mexico ). Classified as Least Concern on The IUCN Red List. By the early 1900s, many populations had been extirpated. Populations have been reestablished in all states where they had become extinct and even introduced in areas where they did not occur historically; introductions often have been from individuals that were not of the original genetic stock. There are an estimated 15,500 Bighorn Sheep in Canada and 42,700 in the USA . There are about 6700 in Mexico , of which 2500 occur in Baja California and 4200 in Sonora ; 2200 of the sheep in Sonora are free-ranging, and 2000 are in enclosures. They were extirpated in the Mexican states of Chihuahua , Coahuila , and Nuevo Leon , and there are now active reintroduction programs in each of these states. In Coahuila , there are about 450 in enclosures and 150 free-ranging; in Chihuahua there are about 200 in enclosures. Populations have been established on Tiburon Island, owned by the Seri Tribe, and Isla del Carmen, privately owned, in the Sea of Cortez. There are about 600 Bighorn Sheep on Tiburon Island and 400 on Isla del Carmen. Over 350 individuals have been removed from Tiburon Island over the last five years to augment populations in Sonora and reestablish extirpated populations in northern Mexico . The conservation program in Mexico has been the result of high prices paid by hunters. About US $ 4-5 million has been generated from sheep hunts on Tiburon Island and an additional US $ 2-7 million from the sale of live animals. Conservation measures include establishing populations in their former habitats on private and public lands. Bighorn Sheep occur in habitats that are not uniformly distributed and that are increasingly being fragmented, making it impossible for groups to interact and interbreed. Other problems include habitat loss due to human disturbance, including oil, gas, and mineral exploration and exploitation; introduction and dispersal of exotic ungulates; and urban expansion. Exotic ungulates can compete for forage and space, and exotics and domestic livestock can transmit diseases. Bighorn Sheep are vulnerable to several diseases transmitted by domestic animals, especially domestic sheep and die-offs have occurred following the introduction of domestic sheep. Translocations have been more successful when domestic sheep are not closer than 6 km of known Bighorn used areas. Bibliography. Bailey & Klein (1997), Bleich et al. (1997), Buechner (1960), Bunch, Boyce et al. (1999), Bunch, Hoffmann & Nadler (1999), Coltman et al. (2001), Demarchi et al. (2000a, 2000b), Epps, Palsboll et al. (2005), Epps, Wehausen et al. (2008), Favre et al. (2008), Feder et al. (2008), Festa-Bianchet (2008), Festa-Bianchet & King (2007), Festa-Bianchet et al. (2006), Geist (1971), Hall (1981), Hamel et al. (2009), Hogg (1987), Krausman & Bowyer (2005), Krausman & Shackleton (2000), Krausman, Leopold, Seegmiller & Torres (1989), Krausman, Sandoval, & Etchberger (1999), Krausman, Valdez & Bissonette (1996), Loehr et al. (2006), Pelletier (2006), Pelletier & Festa-Bianchet (2004, 2006), Remington (1989), Rieucau & Martin (2008), Ruckstuhl & Festa-Bianchet (2001), Shackleton (1985), Shackleton et al. (1999), Singer et al. (2000), Tarango et al. (2002), Valdez (1997), Valdez & Krausman (1999), Wehausen (2005), Wehausen & Ramey Il (1993, 2000), Wehausen et al. (2000).