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Bighorn Sheep
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Bighorn sheep (Ovis canadensis) is a species of sheep in North America and Siberia with large horns which can weigh up to . Recent genetic testing indicates that there are three distinct subspecies of Ovis canadensis, one of which is endangered: Ovis canadensis sierrae.
The bighorn sheep originally crossed 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.
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Bighorn sheep (Ovis canadensis) is a species of sheep in North America and Siberia with large horns which can weigh up to . Recent genetic testing indicates that there are three distinct subspecies of Ovis canadensis, one of which is endangered: Ovis canadensis sierrae.
The bighorn sheep originally crossed 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, the population crashed by 1900 down to several thousand. Conservation efforts (in part, by the Boy Scouts) have restored the population.
Taxonomy and subspecies
Ovis canadensis is one of three species of mountain sheep in North America and Siberia; the other two species being Ovis dalli, that includes Dall Sheep and Stone's Sheep, and the Siberian Snow sheep Ovis nivicola.
The taxononomy of Ovis canadensis continues to be modified as new genetic and morphologic data becomes available but most scientists currently recognize the following subspecies of bighorn:
In addition, there are currently two federally endangered populations:
- Sierra Nevada Bighorn Sheep (Ovis canadensis sierrae), recognized as a unique subspecies
- Peninsular Bighorn Sheep, a distinct population segment of Desert Bighorn Sheep (Ovis canadensis nelsoni)
Origin
Wild sheep crossed the Bering land bridge from Siberia during the Pleistocene (~750,000 years ago) and, subsequently, spread through western North America as far south as Baja California and northern mainland Mexico. Divergence from their closest Asian ancestor (Snow sheep) occurred about 600,000 years ago. In North America, wild sheep have diverged into two extant species -- Dall Sheep that occupy Alaska and northwestern Canada, and Bighorn Sheep that range from southern Canada to Mexico. However, the status of these species is questionable given that hybridization has occurred between them in their recent evolutionary history.
History
Two hundred years ago, Bighorn Sheep were widespread throughout the western United States, Canada, and northern Mexico. Some estimates placed their population at higher than 2 million. However, by around 1900, hunting, competition from domesticated sheep, and diseases had decreased the population to only several thousand. A program of reintroductions, natural parks, and reduced hunting, together with a decrease in domesticated sheep near the end of World War II, allowed the Bighorn Sheep to make a comeback, though not before Ovis canadensis auduboni, a sub-species that lived in the Black Hills, went extinct.
Boy Scouts
In 1936, the Arizona Boy Scouts mounted a state-wide campaign to save the Bighorn Sheep. The Scouts first became interested in the sheep through the efforts of Major Frederick Russell Burnham, the noted conservationist who has been called the Father of Scouting. Burnham observed that fewer than 150 of these sheep still lived in the Arizona mountains. He called George F. Miller, then scout executive of the boy scout council headquartered in Phoenix, with a plan to save the sheep. Burnham put it this way:
I want you to save this majestic animal, not only because it is in danger of extinction, but of more importance, some day it might provide domestic sheep with a strain to save them from disaster at the hands of a yet unknown virus.
Several other prominent Arizonans join the movement and a save the bighorns poster contest was started in schools throughout the state. Burnham provided prizes and appeared in store windows from one end of Arizona to the other. The contest-winning bighorn emblem was made up into neckerchief slides for the 10,000 boy scouts, and talks and dramatizations were given at school assemblies and on radio. The National Wildlife Federation, the Izaak Walton League, and the National Audubon Society also joined the effort.
These efforts led to the establishment of two Bighorn game ranges in Arizona: Kofa National Wildlife Refuge and Cabeza Prieta National Wildlife Refuge. On January 18, 1939, over were set aside and a civilian conservation corp side camp was set up to develop high mountain waterholes for the sheep. The Desert Bighorn Sheep is now the official mascot for the Arizona Boy Scouts.
Characteristics and lifestyle
Bighorn Sheep are named for the large, curved horns borne by the males, or rams. Females, or ewes, also have horns, but they are short with only a slight curvature. 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. Rocky Mountains Bighorn females weigh up to , and males occasionally exceed . In contrast, Sierra Nevada Bighorn females weigh about with males weighing around . Males' horns can weigh up to , as much as the rest of the bones in the male's body.
Bighorn sheep graze on grasses and browse shrubs, particularly in fall and winter, and seek minerals at natural salt licks. Bighorns are well adapted to climbing steep terrain where they seek cover from predators such as coyotes, eagles, and cougars. They live in large herds, but do not have the strict dominance hierarchy of the mouflon: that is, they do not automatically follow a single leader ram, unlike the Asiatic ancestors of the domestic sheep.
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. Bighorn ewes exhibit 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. The lambs are then weaned when they reach 4-6 months.
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).
Scientific analysis
Bighorn Sheep 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. 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.
In 1940, Cowan taxonomically split the species into seven subspecies:
- Rocky Mountain Bighorn Sheep Ovis canadensis canadensis. Habitat: from British Columbia to Arizona.
- California Bighorn Sheep Ovis canadensis californiana. Owens defined the habitat from British Columbia down to California and over to North Dakota. The definition of this subspecies has been updated (see below).
- Nelson's Bighorn Sheep Ovis canadensis nelsoni, the most common Desert Bighorn Sheep, ranges from California through Arizona.
- Mexicana Bighorn Sheep Ovis canadensis mexicana, range from Arizona and New Mexico down to Sonora and Chihuahua.
- Peninsular Bighorn Sheep Ovis canadensis cremnobates. Habitat: the Peninsular Ranges of California and Baja California.
- Weems' Bighorn Sheep Ovis canadensis weemsi. Habitat: Baja California.
- Audubon's Bighorn Sheep Ovis canadensis auduboni. Habitat: North and South Dakota, Montana, Wyoming, Nebraska. Extinct since 1925.
However, starting in 1993, Ramey and colleagues, using DNA testing, have shown that this division into seven subspecies is largely illusory. The latest science shows that Bighorn Sheep is one species, with 3 subspecies O. c. canadensis, O. c. nelsoni, and O. c. sierrae. O. c. sierrae is a genetically distinct subspecies that only occurs in the Sierra Nevada. O. c. nelsoni occur throughout the southwestern desert regions of the U.S. and Mexico, whereas O. c. canadensis occupy the U.S. and Canadian Rocky Mountains and the northwestern U.S.
Bighorn Sheep in culture
Bighorn Sheep were amongst the most admired animals of the Apsaalooka, or Crow, people, and what is today called the Bighorn Mountain Range was central to the Apsaalooka tribal lands. In the Bighorn Canyon National Recreation Area book, storyteller Old Coyote describes a legend related to the Bighorn Sheep. A man possessed by evil spirits attempts to kill his heir by pushing the young man over a cliff, but the victim is saved by getting caught in trees. Rescued by Bighorn sheep, the man takes the name of their leader, Big Metal. The other sheep grant him power, wisdom, sharp eyes, sure footedness, keen ears, great strength, and a strong heart. Big Metal returns to his people with the message that the Apsaalooka people will survive only so long as the river winding out of the mountains is known as the Bighorn River.
Bighorn Sheep are hunted for their meat and horns, which are used in ceremonies, as food, and as hunting trophies. They also serve as a source of eco-tourism, as tourists come to see the famed Bighorn Sheep in their native habitat.
The Rocky Mountain Bighorn Sheep is the provincial mammal of Alberta and the state animal of Colorado and as such is incorporated into the symbol for the Colorado Division of Wildlife.
Bighorn Sheep were once known by the scientific identification argali or argalia due to assumption that they were the same animal as the Asiatic Argali (Ovis ammon). Lewis and Clark recorded numerous sightings of Ovis canadensis in the journals of their exploration--sometimes using the name Argalia. In addition, they recorded the use of bighorn sheep by the Shoshone in making bows. William Clark's Track Map produced after the expedition in 1814 indicates a tributary of the Yellowstone River named Argalia Creek and a tributary of the Missouri River named Argalia River, both in what is today Montana. Neither of these tributaries retained these names however. The Bighorn River another tributary of the Yellowstone, and its tributary stream the Little Bighorn River indicated on Clark's map did retain their names, the latter being the namesake of the Battle of the Little Bighorn.
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