ELK AS COYOTE FOOD
ELK CARRION is an important source of winter food for the coyote and also furnishes considerable summer food. There are about 11,000 elk (Cervus canadensis nelsoni) in the northern Yellowstone herd, more than 7,000 of which were counted within the boundaries of the park in the winter of 193738, the remainder having crossed into the Absaroka National Forest north of Gardiner. Those in the park wintered largely on the north side between Mammoth and the Buffalo Ranch. Some of the bulls winter on the higher slopes along the upper Lamar River and on Mount Washburn. Formerly quite a number wintered in Hayden Valley but in late years scarcely any have been found there. A few are found along the Madison River and in thermal spring areas, such as Old Faithful, where the warmth in the ground melts much of the snow.
Each year, mainly in winter, a certain number of animals perish, usually the calves and the older adults. The "winter kill" may be due to a variety of causes, such as old age, necrotic stomatitis and other diseases, heavy tick infestation, and malnutrition. The losses are generally light, but in winters during which snow conditions are unfavorable they may be large. In the winter of 193637, when conditions for elk were favorable, losses were light and the coyotes went hungry. During the winter of 193738, losses were relatively large and so an abundant food supply was available to predators. The heavy crusted snow conditions prevailing during the entire winter, along with the scarcity of browse, such as Douglas fir, willow, and poplar, made conditions especially unfavorable to the elk. As winter progressed, the elk became thinner and the mortality mounted, coming to a peak in April. Elk carrion was so abundant that there were always carcasses on the range, untouched or only slightly eaten by coyotes, even as early as January. The rangers found more than 500 carcasses and in the course of my field work I came upon 282, half of which were found on the poorer range along the Yellowstone River. The number of animals found each month was as follows:
A few elk die during the summer, thus supplementing the staple summer diet of field mice and pocket gophers. A total of 1,153 of the droppings collected, mainly during the spring, summer, and fall months, contained elk remains. In 1937, coyotes were observed feeding on a bull elk on June 3; a cow so weak she fell down several times was seen on July 14; and a thin weak cow still in the winter coat was seen on July 12. Elk hair is frequently found in coyote droppings during the summer. Calves are eaten during the calving season, and this food item will be discussed in considerable detail in the succeeding sections.
There was no evidence that coyotes killed elk calves in winter, and I feel certain that such predation must be light and that only weak or disabled animals, away from the main bands, would be attacked. In the following incident coyotes are reported to have been hunting a calf elk. Unfortunately the condition of the calf is not given. Reports of coyotes molesting elk are very rare. Observations of elk indicate that the relationship between coyotes and elk is usually similar to that described by former Park Naturalist E. J. Sawyer in his comments on the incident reported by Ranger Cottrell. The incident and comment from Cottrell's note (Yellowstone Nature Notes, February 1928, p. 4) follow:
Comments by the park naturalist:
The following observation quoted from a typewritten report on trumpeter swan studies submitted in 1939 by Assistant Park Naturalist Frank R Oberhansley shows a calf elk-coyote relationship similar to that found by Sawyer.
Elk calf mortality. During the calving season the coyote feeds extensively on elk calves as is evident by the occurrence of remains in 290 droppings. In 1937 carcass remains of 14 elk calves were found. The calf mortality noted seemed to be concentrated during the actual calving period, for the remains found were those of animals which were very young. Eight of the carcasses were found on the winter range which the majority of the elk leave before and during the calving period.
It is extremely difficult to determine what proportion of the calves are found as carrion and how many are killed by coyotes. In domestic animals we know that there is a mortality among calves at birth and shortly after birth. In wild animals we know less about this type of mortality, but we do know that there is a definite mortality at birth. In the spring of 1936, I found a calf moose about 2 or 3 days old which had been seen acting sickly the day before. He was one of twins. The mother was still in the vicinity, so the calf had not been deserted. Under the section on antelope an example of antelope fawns dying at birth is given. Presnall (1938), in discussing effects of an overgrazed deer range, writes: "A weakened condition of the deer has already been indicated in the high death losses during the winter of 193637. Also in the summer of 1937 several deaths in parturition were noted."
In regard to calf elk mortality at birth, O. J. Murie in his publication on the coyotes of Jackson Hole, Wyo., gives several instances of calf mortality in which predators were not involved. He writes: "It was discovered that calves of both elk and moose had been dying shortly after birth, and in the spring of 1931 eight dead elk calves were found, but opportunity was afforded to examine only one of these before decomposition began. While no positive conclusions were reached as to the cause of death, it was determined that natural enemies were not responsible. . . . The fact that eight dead calves were counted in a limited area, and that it is difficult to find such carcasses in timbered country, would indicate that the percentage of loss from this unknown ailment was fairly high."
In the spring of 1938 I made some special search for uneaten dead calves. Obviously, however, such a search is almost futile, for the calving ground is very extensive and even though many calves should die at birth it would be only by chance that a person would find a carcass, especially before coyotes had found and eaten it. The first day I searched for dead calves was on May 24. I found one which had just been born, for parts of it were still moist. The mother was feeding nearby and it was from observing her actions that I was able to find her dead offspring in a clump of sagebrush. This animal appeared to be normal but was rather small, weighing only 20 pounds (considerably below the average weight which is 30 pounds or more), and with the following measurements: total length 3-1/2 inches, hind foot 1-7/8 inches, ear 14 inches.
On May 28 from the top of a butte in the Horseshoe I saw two ravens fly to a distant spot and alight on the ground. On going to the spot, I observed that they had been feeding on a dead calf elk. The only marks were small breaks in the skin on the back and on the abdomen where the ravens had been feeding. The hair was slipping so that it had probably been dead a week. It was either born prematurely or had developed abnormally. The body was but little thicker than the legs, the carcass probably weighing about 10 pounds. Measurements were as follows: Total length 33 inches, hind foot 1-1/2 inches.
A few days later in Hayden Valley, Assistant Park Naturalist Oberhansley was attracted to the carcass of another calf elk. About half the carcass remained and it had decayed considerably. If killed by coyotes one would expect that it would have been eaten before any decay had set in, so it seems that this is another record of a calf that had died at birth.
The hard winters may increase the death rate of calves, since it has been found in studies of domestic animals that deficiencies in nutrition cause abortions and weakened calves. Furthermore, contagious abortion has been found in the elk so that some calves may be lost as a result of this disease.
In Jackson Hole O. J. Murie found each winter a few aborted calves. I have frequently seen coyotes in late winter among the elk herds and think it probable that the coyotes are attracted by the chance of finding an aborted calf or a carcass of an old animal. O. J. Murie writes about contagious abortion as follows: "Field observations, however, supplemented these tests, and each winter a number of aborted fetuses were found10 or more being found in one winter. Considering that such fetuses are not readily found and that ravens often do away with the remains in a short time, it seems safe to conclude that a considerable number of abortions occur. An employee at the elk refuge observed one, but when the fetus was sought later in the day, it had disappeared. . . . One cow examined had died of necrotic stomatitis. Only a few feet behind her lay the aborted fetus." In certain cases the elk calf remains found in droppings might represent fetuses found by coyotes in dead cows, for some of the cows dying in the spring carry fetuses. Also some cows may die during the trials of labor and leave a calf to die.
Besides the calves dying at birth a few are no doubt occasionally lost accidentally or possibly at times are deserted. On May 27, 1938, Assistant Park Naturalist Oberhansley and I found a calf elk in a badger hole a few feet from where I had seen the animal the previous day. One leg was straight out behind in the hole in such a position that it did not seem probable that the calf could extricate itself unassisted. When we stood it up, its hind quarters quivered and it walked as though quite weak. This calf might have become carrion for coyotes if we had not happened along to help it.
On May 28, 1937, a band of 95 elk were following the Lamar River looking for a place to ford. As the river was high, the elk were hesitant in crossing. A cow some distance to the rear was followed by a wobbly calf, which kept lying down after following 10 or 20 yards at a time. The cow wanted to move forward with the herd. She looked alternately toward the herd and the calf until a group of five cows passed her on a trot. Following them, she joined the main herd one-third of a mile from the calf. The cows finally crossed the swollen Lamar River and it was not known if the mother returned to her offspring. The herd instinct and the migration habit were pulling strongly, and in this case it seemed that the calf may have been deserted although desertion of young is probably a rare occurrence.
There is a natural calf mortality at birth, and although there are relatively few records, those existing seem to be sufficient to indicate that a number of dead elk calves are available on the range as carrion.