Colours of Wildlife: Bighorn Sheep
Created | Updated Nov 27, 2016
Bighorn Sheep
Willem is a wildlife artist based in South Africa. He says "My aim is simply to express the beauty and wonder that is in Nature, and to heighten people's appreciation of plants, animals and the wilderness. Not everything I paint is African! Though I've never been there, I'm also fascinated by Asia and I've done paintings of Asian rhinos and birds as well. I may in future do some of European, Australian and American species too. I'm fascinated by wild things from all over the world! I mainly paint in watercolours. . . but actually many media including 'digital' paintings with the computer!"
Here I've another American critter for you! This is a Bighorn Ram. Bighorn Sheep, Ovis canadensis, constitute one of only two wild sheep species occurring in the New World. The other one is Dall's Sheep (or the Thin-horned Sheep) which occurs further to the north, and which is often pure white – sometimes brownish-grey. Bighorns are characteristic of the Rocky Mountains in the USA and Canada, also extending into the Sierra Nevada and in the dry Southwest down into North-western Mexico.
Heavy Horns
Bighorn sheep rams have very thick and heavy horns. These can reach a combined weight of 30 lbs/14 kg in a sheep of a bodyweight of 300 lbs/140 kg … as much as the entire rest of the skeleton! These are not the biggest horns of any wild sheep, though. The Argali of Asia, the largest of the world's wild sheep, have much longer horns, that make several complete turns, and spread out wide to the side. Don't worry, I'll feature those ones in this column as well, before too long, I hope!
The horns are so thick only in the rams. The ewes have much shorter, thinner horns. The horns are indeed a sexual feature: ewes certainly get turned on by the rams with the biggest horns! But the rams also use their horns in direct combat. Two rams wishing to settle who's the meanest and most dominant, go into a kind of 'duel' ritual. First they walk away from each other. After a short distance they turn round, and then lunge at each other, head-first! They crash into each other, horn to horn. The very heavy horns absorb the shock … the sheep also have bony cavities (sinuses) in their skulls, and reinforcing bony struts, to further strengthen their skulls and cushion the shock. Skulls rarely crack, but the horns often sustain some damage.
These fights are mainly for the sake of access to females. The sheep live in large flocks, which are rather egalitarian, without any male being considered the 'leader'. The fights thus mainly happen in the rutting season. But rams can clash horns at other times, too. Even females sometimes fight, for establishing who has the higher status.
Apart from the horn-fighting, bighorns also establish dominance and status by scent: they have scent glands at the inside corners of their eyes, in their groins, and on their feet. With these, each sheep leaves his or her characteristic scent wherever he or she goes. They rub their eye glands on vegetation or other bits of the landscape to leave a dab of secretion.
Immigrants from Asia
Wild sheep are found mostly in Asia. They're characteristic of extreme habitats: steep, rocky and mountainous; dry and deserty; or experiencing extreme winter cold – or all of those together! Domestic sheep are descended from one particular species, the Mouflon, which occurs around the Mediterranean region. Most domestic sheep breeds have more voluminous wool than the wild ones, but wild sheep wool is very fine and dense, and offers excellent insulation to shield the warm sheep bodies against the severe winter cold. There are no true sheep in Africa or in the warmer, moister parts of Asia. In these regions, antelopes, cattle and deer outcompete them. There was, until recently, no wild sheep in North America either. Bighorns are indeed descended from wild sheep that migrated into the continent over the Bering Land Bridge which, during the Ice Ages when sea levels were low, connected north-western North America with what is now Russia. This happened quite recently, geologically speaking: about 750 000 years ago. Since that time the American sheep separated from the Siberian ones, which today are considered a separate species, the Snow Sheep, and also from each other. These three – the Snow Sheep, the Bighorn, and the Dall's Sheep, are still very closely related.
Magnificent Mountaineers
I consider the Bighorn to be one of America's most beautiful and impressive species. Apart from their horns, they're compact and muscular, with a dense, light- to chocolate-brown to greyish wool on most of their bodies; they have white rumps, muzzles, and white lines down the back of their legs. They've small ears, short tails, and bright, alert eyes set wide on their heads so they can see to the front, sides and a bit to the rear at the same time.
Bighorn rams can get quite big, sometimes exceeding 225 kg/500 lbs in bodyweight! Ewes can reach 90 kg/200 lbs. But the ones from the Sierra Nevada are much smaller, the rams seldom exceeding 90 kg/200 lbs and the ewes 140 lbs/65 kg. Still, they're also beautiful!
The main reason why these sheep live mostly in mountainous regions, is to avoid predators. They are expert climbers that can move swiftly up and down very steep slopes. They can't, however, easily move through deep snow, and this is why they avoid the regions experiencing very heavy winter snowfalls, sticking to the somewhat drier climates. Up in the mountains, the only predator that can easily follow and catch them, is the cougar/puma.
They don't always stay in the mountains, though. They like feeding in grassy glades and meadows, but stay close to steep slopes. They graze as well as browse trees and shrubs. In winter they often move to lower elevations to avoid the worst of the cold.
Bears and wolves sometimes manage to catch adult bighorns; lambs are occasionally caught by bobcats, lynxes, and even golden eagles. The eagles have a trick of trying to scare a lamb or a young, inexperienced animal and driving it over a cliff, the fall killing it.
Apart from predation, bighorns sometimes suffer from diseases. These often are carried by domestic sheep, which are not that badly affected, but these diseases can be transmitted to wild bighorns to which they can be fatal – some epidemics kill 90% of affected populations. Healthy bighorn herds are a sign of a healthy and disease-free environment.
Bighorns, like many other native American mammals, suffered much at the hands of humans through hunting as well as disease infecting them from livestock, and by the 1900's were reduced, from an initial population of a couple of millions, to just a few thousand. Fortunately conservation efforts were instituted, the Arizona Boy Scouts doing a big part, and today they're fairly secure. They're admired by tourists and also held in great esteem by Native Americans.
