Although there are many subspecies, Bighorn sheep are one of only two species of mountain sheep that are found solely in North America. Rams (males) can grow to between 5 feet, 3 inches and 6 feet (160 and 180 centimeters) in length from nose to rump, while ewes are generally smaller, at approximately 5 feet (150 centimeters) in length. Bighorn sheep males can weigh as much as 280 pounds (127 kilograms), with their horns alone weighing up to 31 pounds (14 kilograms). Both rams and ewes have horns, although the rams’ horns are bigger and more curved, reaching lengths of up to 30 inches (76 centimeters), with the circumference of the curve being up to 15 inches (18 centimeters). A ram’s horn can serve as a diagnostic feature to tell the age, subspecies, health, and even life history of the animal.
Bighorn sheep are herbivores and diurnal, meaning they are mostly active during the day. Their diets can vary depending on the season as well as the habitat of each subspecies. During seasons with an abundance of food, the sheep will feed on grasses, forbs, and sedges. Then, during harsher seasons like winter, the sheep will spend more time browsing, and feed on tougher, woody plants like rabbit brush. In subspecies living in the deserts, Bighorn sheep will eat brushy plants and cacti, and they will get most of their moisture through their food, though they will still journey to visit watering holes once every several days.
Habitat and Range
Distributed throughout North America, Bighorn sheep can be found in the western provinces of British Columbia and Alberta in Canada, across the western and central states of the United States, and in the northwestern states of Mexico. Although Bighorn sheep are considered a species of "Least Concern" by the International Union for the Conservation of Nature's Red List of Threatened Species, there are several populations and subspecies that are in fact threatened, though their total population size is stable, with over 15,000 individuals in Canada alone. Threats that the Bighorn sheep regularly face include hunting (which can hurt the population as a whole as it usually results in the death of dominant breeding males), habitat loss, and domestic livestock, as the latter compete for their food and spread diseases such as respiratory illnesses unto them.
Bighorn sheep are social animals that live in herds. Ewes and lambs tend to live in larger herds of up to 20 individuals, while rams live in smaller groups of 2 to 5. During the winter, the ewes may band together to form even larger herds of up to 100 individuals. The rams and ewes will live apart for most of the year, until mating season comes around. Bighorn sheep can move up to 15 miles per hour (24 kilometers per hour) while climbing up mountain slopes. With their remarkable surefootedness, they can use ledges of no more than 2 inches (5 centimeters) wide as a foothold from which to leap from one ledge to another, as far as 20 feet (6 meters) away, with no problem.
In the fall, rams begin to compete against each other for the rights to breed with ewes by charging at each other, often reaching speeds of over 20 miles per hour (32 kilometers per hour) in the process. These competitions can last over 24 hours until one of the males concedes, which is usually the younger one with smaller horns. Bighorn sheep are not monogamous, and a female will accept several rams in a given oestrus cycle (when "in heat"). A ewe’s gestation period lasts from 5 to 6 months, after which they will give birth to 1 to 2 lambs in the spring. The female lambs will remain with their mothers' herds, while the males will leave the group when they are between 2 and 4 years old to join a herd of rams.
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