Species Spotlight: Bighorn Sheep

Author: Scott Bowler | Published: June 28, 2021 | Category: Species Spotlight

Bighorn sheep (Ovis canadensis) once ranged far and wide all across the West, inhabiting a wider variety of habitats than they do today. There were many more bighorn as well, but nearly all populations of them were completely wiped out by overhunting (especially for food—apparently they’re pretty tasty—in the 1800s as pioneers settled into the west), habitat loss, and diseases spread from domestic livestock, to which, like many native wildlife species, they have little resistance.

But, before we dive into the bighorn you can encounter in Oregon today, let’s take a quick look back a their evolution over the last half a million years or so.

From Snow Sheep to Thinhorns and Bighorns

Somewhere around 600,000 years ago the snow sheep (Ovis nivicola) migrated across the Bering land bridge (now, of course, the Bering Sea) and began evolving to fit into a variety of suitable habitats throughout North America, spreading as far south as Baja and central Mexico, through the Rockies, Sierra Nevada and other interior western mountain ranges, and into many desert and grassland habitats. Those Ovis nivicola who walked over from Asia have now evolved into two species. One branch stayed closer to “home” becoming the thinhorn or Dall sheep (Ovis dalli) now residing in the mountains of British Columbia, Alberta and western Canada on into Alaska. The other branch (Ovis canadensis) went south and evolved into a complex of several bighorn subspecies.*

Oregon’s Bighorn

The two subspecies that historically occurred in Oregon — Rocky Mountain and California — were quickly exterminated due to unregulated hunting, habitat destruction from grazing, habitat loss from development, and diseases contracted from domestic animals. By about 1912 or so, there were likely none left in our state.

Today, however, Oregon is again home to two subspecies, the Rocky Mountain bighorn, (Ovis canadensis ssp. canadensis) and the California bighorn, (O. c. californiana). Our current populations are descended from animals reintroduced in programs starting in the early 1950s, when the first bighorn were translocated onto the Hart Mountain Wildlife Refuge. This was quite successful and the Hart Mountain herds have since provided stock for other herds throughout the state. They continue to be intensively studied and managed, but recently the herd there has experienced a significant decline, resulting in an open EIS addressing this issue. There are probably fewer than 5,000 animals statewide, spread around in some of our wildest and most remote areas, which makes seeing a herd a rare treat. Bighorn are also a challenging and highly sought after big game species. In Oregon hunting them is literally a “once in a lifetime” opportunity, meaning that a hunter can get only one tag in their lifetime.

The males of both these subspecies can get up to 6-feet long and 3.5-feet tall and generally weigh between 150 and 500 pounds, with females somewhat smaller, up to about 200 pounds and 3-feet tall. They get their name from the large horns that both sexes have. The ewes have smaller and less curled horns, and the rams sport huge horns weighing 30 or more pounds — which is about as much as the rest of their bones. Since rams use these horns as a weapon in dominance battles, they have some impressive skeletal and skull adaptations to protect their brain as they rear up and crash down onto one another. If ever you have the opportunity, these battles are spectacular to watch, and loud (it’s sometimes possible to hear them from up to a mile away!)

voices

Michelle Frisella, member since 2017

Michelle Frisella, member since 2017

So proud of ONDA and its members and volunteers. Such hard work gets done. To use an overused word, this is patriotism!

watch

Stewardship Pronghorn Fence

Stewardship Pronghorn Fence

listen

Wind and Birds in Quaking Aspen

Wind and Birds in Quaking Aspen

Rocky Mountain Bighorn Sheep

Larisa Bogardus

California Bighorn Sheep

Zachary MacCoy   Website

The Rocky Mountain subspecies (O. c. canadensis) prefer the higher, cooler elevations in the northeast section of our state, such as the Wallowa and Blue Mountains. Oregon Department of Fish and Wildlife estimates that there are somewhere around 800 of these large animals in the higher reaches of the Blue and Wallowa Mountain Ranges, and Hells Canyon, with perhaps the largest single herd centered around Baker City.

The California subspecies (O. c. californiana) numbering now maybe 3,500 to 4,000 in Oregon, are distributed around the drier parts of our state in roughly 30 herds. Since there are more of them, this subspecies is the one you are more likely to see. Look primarily around large rocky cliffs and mountains throughout the Great Basin and surrounding areas. Reliable places to see them are along the cliffs next to I-84 between The Dalles and about Arlington (the famous, or infamous in terms of rubber-necking accidents, “Highway Herd”), Steens Mountain, Hart Mountain, John Day River, the east side of Lake Owyhee around Leslie Gulch, and the Pueblo Range. You can, however, encounter them in many other areas throughout the Sagebrush Sea if the habitat is right.

Bighorn’s habitat of choice — large, steep rocky areas with good forage — affords them considerable protection, but they are preyed upon and they do get eaten. Aside from death by encounters with vehicles (especially along roadsides in states that use salt on the roads, as bighorn come down to eat the salt), significant regulated take by hunters, and sometimes considerable mortality from microbes, bighorn also have a variety of predators. Wild hunters of bighorn include cougars, wolves, bobcats, coyotes, bears, possibly wolverines, and even golden eagles. The lambs, obviously, are most easily hunted and killed. A reported tactic of golden eagles is to harass lambs and drive them off of a cliff. Herds will migrate up and down in elevation as seasons, vegetation and water availability dictate, but typically don’t move as far horizontally across the landscape as, say, a herd of elk might travel.

ONDA’s work to conserve the high desert’s biodiversity and most ecologically important landscapes and habitats includes some of the most storied and important bighorn sheep herds in the state. Our work to protect places like the Greater Hart-Sheldon, Owyhee Canyonlands, and John Day River Basin helps to improve the outlook for these icons of the West.

Learn More

  • About Resource Management Plans and ONDA’s ongoing efforts to develop common-sense public lands management to preserve these key habitats.

*Depending on the source you consult, you can find different numbers of subspecies of Ovis canadensis. Back in the 1940s, Ian McTaggart-Cowan split the species into seven subspecies — three mountain bighorns and four desert bighorns. In the 1990s, Ramey et al asserted that the division into seven subspecies “is largely illusory” and used DNA testing to suggest just three subspecies: Rocky Mountain, Sierra Nevada, and Desert. The Department of the Interior has determined that the Sierra Nevada subspecies is a separate subspecies from California subspecies, and not a distinct population segment of the California subspecies, and are listed as endangered. The Integrated Taxonomic Information System (ITIS), lists eight subspecies, but this doesn’t necessarily represent the accepted number today, but shows all subspecies that were ever identifiedYou can expect classifications and names to change over time as biologists continue their research and publish their work.

 

kayaker in red kayak with dog

About the Author

Scott Bowler is a retired science educator now living in Sisters and doing environmental service work for fun. An ONDA member since 2000, he participated in the very first ONDA fence pull on Steens Mountain and has taken part many more since then. In recognition of the many ways he engages in desert conservation, he earned ONDA’s Conservationist of the Year award in 2020.