Post by ansalon on May 14, 2012 15:08:55 GMT -5
Bighorn Sheep - Ovis canadensis
The bighorn sheep (Ovis canadensis), is a species of sheep in North America named for its large horns. These horns can weigh up to 30 pounds (14 kg), while the sheep themselves weigh up to 300 pounds (140 kg). Recent genetic testing indicates that there are three distinct subspecies of Ovis canadensis, one of which is endangered: Ovis canadensis sierrae. Sheep originally crossed to North America over the Bering land bridge from Siberia: the population in North America peaked in the millions, and the bighorn sheep entered into the mythology of Native Americans. However, by 1900 the population had crashed to several thousand. Conservation efforts have restored the population.
Subspecies
Rocky Mountain bighorn sheep (Ovis canadensis canadensis) - occupying the U.S. and Canadian Rocky Mountains and the northwestern U.S.
Sierra Nevada bighorn sheep (Ovis canadensis sierrae) - formerly California bighorn sheep, a genetically distinct subspecies that only occurs in the Sierra Nevada
Desert Bighorn Sheep (Ovis canadensis nelsoni) - occurring throughout the southwestern desert regions of U.S. and Mexico.
Description
Bighorn sheep are named for the large, curved horns borne by the rams (males). Ewes (females) also have horns, but they are shorter with less curvature.[14] They range in color from light brown to grayish or dark, chocolate brown, with a white rump and lining on the back of all four legs. Males typically weigh 127–316 pounds (58–143 kg), are 36–41 inches (91–100 cm) tall at the shoulder, and 69–79 inches (180–200 cm) long from the nose to the tail. Females are typically 75–188 pounds (34–85 kg), 30–36 inches (76–91 cm) tall and 54–67 inches (140–170 cm) long. Male bighorn sheep have large horn cores, enlarged cornual and frontal sinuses and internal bony septa. These adaptations serve to protect the brain by absorbing the impact of clashes. Bighorn sheep have pre-orbital glands on the anterior corner of each eye, inguinal glands in the groin and pedal glands on each foot. Secretions from these glands may support dominance behaviors.
Bighorns from the Rocky Mountains are relatively large, with males that occasionally exceed 500 lb (230 kg) and females that exceed 200 lb (90 kg). In contrast, Sierra Nevada Bighorn males weigh up to only 200 lb (90 kg) and females to 140 lb (60 kg). Males' horns can weigh up to 30 lb (14 kg), as much as the rest of the bones in the male's body.
Ecology
The Rocky Mountains and Sierra Nevada Bighorn occupy the cooler mountainous regions of Canada and the United States. In contrast, the desert bighorn sheep subspecies are indigenous to the hot desert ecosystems of the Southwestern United States. Bighorn sheep generally inhabit alpine meadows, grassy mountain slopes and foothill country near rugged, rocky cliffs and bluffs. Since bighorn sheep cannot move though deep snow, they prefer drier slopes where the annual snowfall is less than about sixty inches a year. A bighorn's winter range usually lies 2,500-5,000 feet in elevation, while its summer range is tends to be 6,000-8,500 feet. Bighorn sheep are highly susceptible to certain diseases carried by domestic sheep such as scabies and pneumonia; additional mortality occurs as a result of accidents involving rock fall or falling off cliffs (a hazard of living in steep, rugged terrain). Bighorns are well adapted to climbing steep terrain where they seek cover from predators. Predation primarily occurs with lambs which are hunted by coyotes, bobcats, lynxes and golden eagles. Bighorn sheep of all ages are threatened by bears, wolves and especially cougars, which are perhaps best equipped with the agility to predate in uneven, rocky habitats. They are considered good indicators of land health because the species is sensitive to many human-induced environmental problems. In addition to their aesthetic value, bighorn sheep are considered desirable game animals by hunters.
Bighorn sheep graze on grasses and browse shrubs, particularly in fall and winter, and seek minerals at natural salt licks. Females tend to forage and walk, possibly to avoid predators and protect lambs, while males tend to eat and then rest and ruminate which lends to more effective digestion and greater increase in body size.
Bighorn sheep live in large flocks, and do not typically follow a single leader ram, unlike the mouflon, the ancestor of the domestic sheep, which has a strict dominance hierarchy. Prior to the mating season or "rut", the rams attempt to establish a dominance hierarchy that determines access to ewes for mating. It is during the prerut period that most of the characteristic horn clashing occurs between rams, although this behavior may occur to a limited extent throughout the year. Ram's horns can frequently exhibit damage from repeated clashes. Females exhibit a stable, non-linear hierarchy that correlates with age. Females may fight for high social status when they are integrated into the hierarchy at 1–2 years of age.
Rocky Mountain bighorn rams employ at least three different courting strategies. The most common and successful is the tending strategy in which a ram follows and defends an estrous ewe. Tending takes a lot of strength and dominance and thus ewes are more receptive to tending males, feeling that they are the most fit. Another tactic is coursing which is when a rams fights for an already tended ewe. Ewes tend to avoid coursing males so the strategy is not effective. Rams will also employ a blocking strategy. They will prevent a ewe from accessing tending areas before she even goes into estrous.
Bighorn ewes have a six-month gestation. In temperate climates, the peak of the rut occurs in November with one, or rarely two, lambs being born in May. Most births occur in the first two weeks of the lambing period. Pregnant ewes of the Rocky Mountains migrate to alpine areas in spring, presumably to give birth in areas safer from predation but are away from areas with good quality forage. Lambs born earlier in the season are more likely to survive than lambs born later. Lambs that are born late may not have access to sufficient milk as their mothers are lacatating at a time when food quality is lower. Newborn lambs weigh from 8 to 10 pounds (3.6 to 4.5 kg) and can walk within hours. The lambs are then weaned when they reach 4–6 months. The lifespan of rams is typically 9–12 years, with 10–14 years for ewes.
The bighorn sheep (Ovis canadensis), is a species of sheep in North America named for its large horns. These horns can weigh up to 30 pounds (14 kg), while the sheep themselves weigh up to 300 pounds (140 kg). Recent genetic testing indicates that there are three distinct subspecies of Ovis canadensis, one of which is endangered: Ovis canadensis sierrae. Sheep originally crossed to North America over the Bering land bridge from Siberia: the population in North America peaked in the millions, and the bighorn sheep entered into the mythology of Native Americans. However, by 1900 the population had crashed to several thousand. Conservation efforts have restored the population.
Subspecies
Rocky Mountain bighorn sheep (Ovis canadensis canadensis) - occupying the U.S. and Canadian Rocky Mountains and the northwestern U.S.
Sierra Nevada bighorn sheep (Ovis canadensis sierrae) - formerly California bighorn sheep, a genetically distinct subspecies that only occurs in the Sierra Nevada
Desert Bighorn Sheep (Ovis canadensis nelsoni) - occurring throughout the southwestern desert regions of U.S. and Mexico.
Description
Bighorn sheep are named for the large, curved horns borne by the rams (males). Ewes (females) also have horns, but they are shorter with less curvature.[14] They range in color from light brown to grayish or dark, chocolate brown, with a white rump and lining on the back of all four legs. Males typically weigh 127–316 pounds (58–143 kg), are 36–41 inches (91–100 cm) tall at the shoulder, and 69–79 inches (180–200 cm) long from the nose to the tail. Females are typically 75–188 pounds (34–85 kg), 30–36 inches (76–91 cm) tall and 54–67 inches (140–170 cm) long. Male bighorn sheep have large horn cores, enlarged cornual and frontal sinuses and internal bony septa. These adaptations serve to protect the brain by absorbing the impact of clashes. Bighorn sheep have pre-orbital glands on the anterior corner of each eye, inguinal glands in the groin and pedal glands on each foot. Secretions from these glands may support dominance behaviors.
Bighorns from the Rocky Mountains are relatively large, with males that occasionally exceed 500 lb (230 kg) and females that exceed 200 lb (90 kg). In contrast, Sierra Nevada Bighorn males weigh up to only 200 lb (90 kg) and females to 140 lb (60 kg). Males' horns can weigh up to 30 lb (14 kg), as much as the rest of the bones in the male's body.
Ecology
The Rocky Mountains and Sierra Nevada Bighorn occupy the cooler mountainous regions of Canada and the United States. In contrast, the desert bighorn sheep subspecies are indigenous to the hot desert ecosystems of the Southwestern United States. Bighorn sheep generally inhabit alpine meadows, grassy mountain slopes and foothill country near rugged, rocky cliffs and bluffs. Since bighorn sheep cannot move though deep snow, they prefer drier slopes where the annual snowfall is less than about sixty inches a year. A bighorn's winter range usually lies 2,500-5,000 feet in elevation, while its summer range is tends to be 6,000-8,500 feet. Bighorn sheep are highly susceptible to certain diseases carried by domestic sheep such as scabies and pneumonia; additional mortality occurs as a result of accidents involving rock fall or falling off cliffs (a hazard of living in steep, rugged terrain). Bighorns are well adapted to climbing steep terrain where they seek cover from predators. Predation primarily occurs with lambs which are hunted by coyotes, bobcats, lynxes and golden eagles. Bighorn sheep of all ages are threatened by bears, wolves and especially cougars, which are perhaps best equipped with the agility to predate in uneven, rocky habitats. They are considered good indicators of land health because the species is sensitive to many human-induced environmental problems. In addition to their aesthetic value, bighorn sheep are considered desirable game animals by hunters.
Bighorn sheep graze on grasses and browse shrubs, particularly in fall and winter, and seek minerals at natural salt licks. Females tend to forage and walk, possibly to avoid predators and protect lambs, while males tend to eat and then rest and ruminate which lends to more effective digestion and greater increase in body size.
Bighorn sheep live in large flocks, and do not typically follow a single leader ram, unlike the mouflon, the ancestor of the domestic sheep, which has a strict dominance hierarchy. Prior to the mating season or "rut", the rams attempt to establish a dominance hierarchy that determines access to ewes for mating. It is during the prerut period that most of the characteristic horn clashing occurs between rams, although this behavior may occur to a limited extent throughout the year. Ram's horns can frequently exhibit damage from repeated clashes. Females exhibit a stable, non-linear hierarchy that correlates with age. Females may fight for high social status when they are integrated into the hierarchy at 1–2 years of age.
Rocky Mountain bighorn rams employ at least three different courting strategies. The most common and successful is the tending strategy in which a ram follows and defends an estrous ewe. Tending takes a lot of strength and dominance and thus ewes are more receptive to tending males, feeling that they are the most fit. Another tactic is coursing which is when a rams fights for an already tended ewe. Ewes tend to avoid coursing males so the strategy is not effective. Rams will also employ a blocking strategy. They will prevent a ewe from accessing tending areas before she even goes into estrous.
Bighorn ewes have a six-month gestation. In temperate climates, the peak of the rut occurs in November with one, or rarely two, lambs being born in May. Most births occur in the first two weeks of the lambing period. Pregnant ewes of the Rocky Mountains migrate to alpine areas in spring, presumably to give birth in areas safer from predation but are away from areas with good quality forage. Lambs born earlier in the season are more likely to survive than lambs born later. Lambs that are born late may not have access to sufficient milk as their mothers are lacatating at a time when food quality is lower. Newborn lambs weigh from 8 to 10 pounds (3.6 to 4.5 kg) and can walk within hours. The lambs are then weaned when they reach 4–6 months. The lifespan of rams is typically 9–12 years, with 10–14 years for ewes.