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 in the 1800s, 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.*
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!)