Wildlife Portfolio of the Western National Parks
NPS Logo



THE ROCKY MOUNTAIN BIGHORN, commonly called mountain sheep, is the most famous of all the mammals living in Rocky Mountain National Park. This species occurs also in Grand Teton, Yellowstone, and Glacier National Parks in the United States and in several of the Canadian National Parks.

The general coloration of Rocky Mountain bighorn is brownish or grayish brown on the back, yellowish white on the under parts, with a whitish patch on the rump which is very conspicuous. The tail is short and dark. The brownish hairs are darkest on the head, throat, legs, and along a narrow strip down the center of the back. The body is densely covered with coarse hair and on some specimens there has been found a slight undercoat of woolly hairs. The eyes are golden yellow, the horns brown, and the hoofs black.

This large wild sheep is not likely to be confused with any other mammal. The adult rams have a length of from 60 to 70 inches; height at shoulder from 38 to 42 inches; a stocky body usually weighing between 200 and 300 pounds; and massive, circular horns which curve backward about the side of the head. (See illustration). The females, often called "ibex," are shorter and more slender than the rams, weighing only about two-thirds as much, and they possess small slender, slightly curved horns. (See page 72.)

This species formerly was much more numerous than it is today. On account of the excellent quality of its meat, the bighorn was considered by hunters to head the list of wild game. This together with the fact that the massive horns of the rams were considered by hunters to be an outstanding trophy, resulted in these animals being widely hunted and greatly reduced in numbers throughout their range. However, this general destruction has been offset, at least in part, by the protection afforded them in our national parks, where a fair bighorn population is now to be found, although it is not up to the carrying capacity of the range in all cases.

Generally speaking, the bighorn is now a resident of the higher mountains and in summer is found at or above timber line where these wild sheep seek suitable alpine pastures and where broken cliffs serve as a protection against predatory enemies. In winter they seek to avoid soft deep snow for it not only cuts off their food supply but also renders them more liable to attack by predators. However, prevailing winter winds often sweep bare certain high alpine slopes, thereby leaving forage available, which enables some of the bighorns to winter on the mountain tops. It has been our experience in Rocky Mountain National Park that many bighorns still try to descend in winter to the foothills to find food and escape danger from deep snow.


BIGHORNS usually are most active in the early morning, and experience with these animals in Glacier National Park indicates their greatest feeding activity occurs before noon, and often by 10 a. m. or thereabouts they retire to the base of some protecting cliff and bed down. On September 1, 1931, at Glacier National Park, I found that a band of bighorns came down regularly during the night or early morning to a mineral spring near a lake. However, by sunup the band was always back up on the mountain side. This flock consisted of six ewes, six lambs, and two young rams. The lambs were well grown but still nursing.

The feeding habits of the bighorns are peculiar in that a relatively small amount of time is spent in grazing and a relatively large proportion of time is spent in chewing their cuds. Usually this latter process is done when the sheep are bedded down, and it has been found that each cud is chewed for about 1 minute. One advantage of this system of feeding is that the animals can gather a large amount of rough herbage in a relatively short time and later during the middle of the day they can thoroughly chew this food at their leisure. How I envy them at my "rush" lunch period!

At Poudre Lake in Rocky Mountain National Park at 2 p. m. on July 6, 1930, I saw a band of 14 Rocky Mountain bighorns and followed them to the upper slopes of Specimen Mountain which is 12,482 feet high. About 4:30 p. m. they resumed feeding on the patches of green turf amid the rock slides. Seeing me, the animals ran rapidly up to the rim and stood on the skyline, but when I quietly withdrew they soon returned to their feeding.

The old rams at certain seasons keep together in a band by themselves and do not run with the females and lambs. At Specimen Mountain in Rocky Mountain National Park one afternoon I counted 28 bighorns—8 lambs of the year and 20 females and yearlings.

One lamb is usually born to a ewe each year, about the first of June, but twins are not infrequent. On Mount Washburn, Yellowstone National Park, on July 5, 1934, a park ranger saw two bighorn lambs, one of which he estimated to be about 2 weeks old and the other slightly older. One of the ewes called to her young, with a bleat similar to that of a domestic sheep but lower in tone.

Numerous instances of hybrids between Rocky Mountain bighorn and domestic sheep have been reported. Actual breeding between bighorn and domestic sheep has been observed. In one instance at least seven hybrid lambs were definitely known to have been born as a result.

J. D. Figgins, formerly Director of the Colorado Museum of Natural History, informed me that some of these hybrids grew up, bred, and were fertile. Domestic sheep not only seriously compete with the bighorns for food but the fact that they interbreed with the wild sheep and that the hybrids are fertile indicates that the relationship is sufficiently close so that parasites or disease might be transmitted from one animal to another and may account for the decrease in the number of bighorns. There is also the real danger of weakening the native bighorn stock through its breeding with the inferior domestic sheep.


<<< Previous <<< Contents>>> Next >>>

Last Updated: 01-Jul-2010