Fauna Series No. 4

Fauna of the National Parks — No. 4 Ecology of the Coyote in the Yellowstone

CHAPTER VIII:
BIGHORN IN RELATION TO COYOTES

STATUS OF BIGHORN

During the winter the bighorn, especially in the Mount Everts region, subsist mainly on grass, but also feed on a variety of shrubs and trees such as willow, greasewood, sagebrush, fringed sage, yellowbrush, and Douglas fir. The stomach contents of a ram that died near Golden Gate consisted of 50 percent Douglas fir, and animals were several times seen feeding on fir branches which had fallen to the ground. Sagebrush and other shrubs were eaten extensively in November before snow had fallen on the grasses, and on Junction Butte and vicinity large quantities of yellowbrush were eaten during early November.

In winter, the bighorn are in direct competition with the elk for practically all food plants, and with the deer and antelope for the browse plants where their ranges overlap. The competition for food each winter is severe. On Mount Everts the bighorn during the last half of the winter subsist on a range so heavily utilized that the elk for the most part avoid it, after taking the "cream" of the forage. The bighorn in late winter pick at discarded seed stems lying on the ground and at the already closely grazed grass. The natural diet of the bighorn is more varied than the present vegetation on Mount Everts permits. A diet of greater variety would probably be more balanced in food values and result in healthier animals more resistant to diseases.

The grass slopes of Mount Everts were apparently once largely covered with sagebrush, remnants of which still remain in the form of dead roots and broken stalks. Now sagebrush is found only in hollows and ravines protected in winter by heavy snows. Destruction of the sagebrush was brought about by the combined feeding of bighorn, antelope, deer, and elk. When present it served to insure a good grass growth by retaining the snow, and shading the ground in summer so that surface evaporation and run-off were retarded. The nearly complete utilization of the grass each winter is adversely affecting the grass stand and is increasing erosion. A protected plot on the Mount Everts range showed clearly, in the fall of 1938, that heavy grazing was deteriorating the grass stand. The grass within the plot which had not been grazed for about 4 years was luxurious, while that outside was sparse and showed poor growth. So heavily is the range grazed in winter that no dead vegetation is left on the ground to retard run off and evaporation during the growing season. Hence the growth is poor if moisture does not fall regularly. As a result of the heavy grazing on the range, not only is the grass stand deteriorating but sheet erosion is quite evident. The heavy use not only affects the bighorn's supply of food each winter but also reduces the permanent carrying capacity of the range.

In the Tower Falls area, Douglas fir on the bighorn range is overbrowsed, but the grasses and low plants are not greatly injured. They are protected from over use by deep snows and a smaller concentration of animals, and the cooler climate makes them less subject to drought and heat during the growing season. On this range the bighorn suffer somewhat through other forms of competition from the elk. In the fall of 1937 large bands of elk were seen feeding on grasses and yellowbrush on the narrow strip of range along the rock rim above the Yellowstone River, which is the important part of the range for bighorn. Although the vegetation was only partially consumed, enough was eaten to make considerable difference to the animals when they pawed through the snow for food in midwinter.

Condition of the ranges is an important factor to consider in discussing the status of the bighorn. Disease, in many cases, is the result of poor range, and poor range would probably always augment the extent of disease. As yet the effect of poor range on bighorn reproduction is unknown. There is a possibility that inadequate nutrition in winter might reduce the lamb crop or produce lambs with lessened vitality. The bighorn are afflicted with mites which each year destroy a few animals. Many, especially the lambs, have a severe cough, the causative organisms of which may also be taking its toll. To minimize the effects of disease it is important to improve the range and to discourage congestion of the animals over a small area for any length of time. Resort to such devices as salting should be avoided.

Poaching is a factor in holding down the number of bighorn on the Mount Everts area. A few bighorn occasionally move outside the park into territory along the Yellowstone River where the animals are known to have been poached in the past. As many as 15 animals consisting of nine large rams, three ewes, two lambs, and one yearling have been seen outside the park at one time. During the winter of 1934—35, eight from the Mount Everts population were killed by poachers just outside the park, and another died from shot wounds. Some bighorn were said to have been illegally shot during the winter hunting season of 1937—38. Later I found no evidence of bighorn poaching but did discover in the areas occupied by bighorn just outside the park boundary, the legs and head of a fawn deer that had been slain in the early spring. Two rams were reported illegally killed outside the park in the winter of 1938—39. Where a population is barely holding its own, a small but steady drain may be sufficient to keep it from increasing.

During the last 2 or 3 years the bighorn population has held its own or possibly increased slightly. In view of the lack of forage in the Mount Everts area there is hardly room for more bighorn on that important winter range. There is a strong indication that the lambs are affected by some disease or parasite causing a severe cough, which, judging from the scarcity of lambs appearing on the winter range, may be eliminating some of them during the fall. The data obtained from the coyote droppings, from observations of the coyotes on the bighorn ranges, and from lamb counts at various times, indicate that coyote predation is at most an unimportant mortality factor, this in spite of a large population of coyotes on the big horn ranges.

Last Modified: Thurs, Dec 20 2001 10:00:00 pm PDT
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