Fauna Series No. 5

Fauna of the National Parks — No. 5 The Wolves of Mount McKinley

CHAPTER THREE:
DALL SHEEP (continued)

Relation with Animals of Minor Importance

SNOW BUNTINGS COMPETE FOR FOOD

On October 11, 1939, a flock of about 100 snow buntings (Plectrophenax n. nivalis) in a high pass were feeding on the heads of Calamagrostis. A large patch had been quite thoroughly threshed by the snowbirds. Here was competition for food between animals which we would not expect to have much relation with one another. I had noticed that the sheep had been feeding extensively on these same grass heads which stuck up through the snow. Calamagrostis is a very common grass, so there is much of is available. But it so happened that the particular patch eaten by the snow buntings was up high where it would be available to the sheep when deep snows covered that growing lower down. However, this competition is no doubt extremely slight and is mentioned here only to show an unexpected relationship.

WOLVERINE AND SHEEP

The wolverine (Gulo hylaeus) is widely distributed in the mountains in the park. In 1940 and 1941, after a period of low numbers, is was reported to be on the increase. It was reported as abundant in 1927 and 1928, but I do not know when the numbers became reduced. Wolverine abundance may have been correlated with the high sheep population when much carrion was undoubtedly available. Several times I found the scattered remnants of a sheep carcass which had been investigated by a wolverine, but I have no authentic data on the relationship of the wolverine to the sheep. One circumstance cited as evidence that wolverines prey on sheep is that the former are commonly found on mountains near timber line where mountain sheep range. However, it should be added that wolverines occupy a similar habitat in areas where there are no sheep. The number killed by wolverines under any circumstance is undoubtedly small.

LYNX AND SHEEP

During the period of this study the lynx (Lynx canadensis canadensis) was very scarce; not a single track was noted.

In the winter of 1907—8, Sheldon (1930) found two sheep which had been killed by lynxes. One of the victims was a 2-year-old ewe and the other a ram, about 2 years old. In each case, the predator had lain in ambush, leaped from above to the sheep's back, and had bitten the sheep around the eyes.

Ordinarily the lynx feeds on snowshoe hares, but when the hares become scarce during the ebb of their cycle, the lynxes are left without this usual food supply. Under these conditions, they are forced to seek other food. The fact that hares were scarce in 1907—8 probably accounts for the lynxes hunting sheep at that time. After the hares disappear the lynxes also go into a decline, so their predation on sheep is only for a short time and probably is never a serious factor.

In 1927 there was a big die-off in the hare population. It is reported that hares were unusually abundant in the fore part of the summer but that during August they became extremely scarce. It is interesting to note that in the Superintendent's reports for 1927 and 1928 the lynx was reported increasing. Possibly due to the hare die-off, lynxes began to wander about in search of food, especially in the sheep hills, and so were noticeable. After 1928 there is no mention of lynx abundance, and they have been scarce since that time.

COYOTE AND SHEEP

The coyote, Canis latrans incolatus Hall, was so scarce in the sheep hills that there was no opportunity to study its possible effect on the mountain sheep population. I saw a coyote on three occasions at Sable Pass, and once near Teklanika Canyon. These were the only coyotes seen during the three summers and one winter which I spent in the field. In recent years they have been reported somewhat common near the northeast corner of the park where snowshoe hares have been present in moderate numbers; and in the low country north of the park a few are reported by trappers.

The coyote frequently has been listed as a destroyer of the Rocky Mountain bighorn in the States, but the few studies which have been made indicate that the coyote is not a serious enemy of these sheep. In Yellowstone National Park I found no evidence of coyote predation on the bighorn, not even in summer when lambs in some situations seemed to be vulnerable to coyote attack, and coyotes on these summer ranges were common (Murie, 1941). Other investigators in Yellowstone National Park have not found evidence that coyotes were a serious menace to the mountain sheep. In Jackson Hole, Wyo., coyotes were suspected of destroying many lambs, but investigations indicated that the lambs were dying of disease rather than coyote predation (Honess and Frost, 1942). In a study of a prospering bighorn herd in Colorado, where coyotes are common in the sheep area, known losses from coyotes were small (Spencer, 1943).

The scarcity of coyotes in the sheep hills in Mount McKinley National Park may indicate that they cannot find sufficient food there. Of course in the absence of the wolf, there would be more weak sheep and carrion available to them, and more coyotes might then occupy the sheep hills. For this food supply they probably cannot compete with the wolf, since they are a weaker predator in respect to the sheep. It is possible that the wolf tends to drive out the coyote by attacking it, although both species once occupied the same general territory in the States. I am inclined to believe that the main reason that the coyotes are not in the sheep hills is that the staple rodent supply is more abundant in the lower country. Possibly coyote distribution is much influenced by the distribution of snowshoe hares also.

In 1932, when many sheep were succumbing to the unusually severe winter conditions and others were weakened by them, it is reported that some sheep were killed by coyotes. Such predation on weakened animals is not at all unlikely, but the information at hand does not indicate any consistent or serious predation by coyotes on the mountain sheep herds of Mount McKinley National Park.

GOLDEN EAGLE AND SHEEP

Lambs Well Protected When Young.—Charles Sheldon (1930, p. 33) writes as follows concerning his observations on relationships between the golden eagle (Aquila chrysaetos canadensis) and white sheep: "While hunting sheep in the Yukon Territory during the two previous years, and also while in the Alaska Range that summer, I observed the relations between golden eagles and sheep, not once noticing any antagonism between them—but only complete indifference." On May 25, 1908, Sheldon saw an eagle swooping at some ewes and lambs and states that it was the first time that he had seen an eagle swoop at sheep or even notice them. The ewes stood over their lambs to protect them from the eagle. On June 7, 1908, Sheldon (1930, p. 382) reports seeing eagles swooping at lambs but states that no capture was made, and that the ewes were very watchful when the eagle was near. An eagle's nest was nearby and near it Sheldon found lamb remains. He shot the eagle on the nest and found the stomach filled with ground squirrel remains. He concluded that it was probably true that the eagles preyed heavily on young lambs but that they were seldom molested by them after they were a month old. The evidence to support his conclusions that "it is undoubtedly true that golden eagles take a heavy toll of the newly born lambs" was his observation of some eagles swooping at ewes and lambs, and the lamb remains found at the one nest. His other experiences had caused him to conclude that eagles did not molest the sheep.

Joseph S. Dixon (1938) spent the summers of 1926 and 1932 making wildlife studies in Mount McKinley National Park. In 1932 he made observations on four eagle nests but found no fresh lamb remains in or below them. However, it should be taken into account that the lamb crop that year was very poor, so fewer lambs than usual were available to the eagles. Dixon (1938, p. 46) draws the following conclusion concerning eagle-sheep relationships; "Our experience in the region both in 1926 and in 1932 indicated that during these two seasons lambs were rarely taken by eagles, which were found to live chiefly upon ground squirrels and marmots."

Former Ranger Lee Swisher stated that he had visited several eagle nests but never found any lamb remains at them.

I have observed eagles dive at ewes and lambs, but such maneuvers do not necessarily gage the degree of eagle predation on lambs. Eagles have also been observed swooping low over grizzlies and wolves at times when there was no intent of predation. Once an eagle dove at an adult wolf which was standing near its den. About a dozen times the eagle swooped, barely avoiding the wolf which each time jumped into the air and snapped at it. The eagle turned upward at the right moment to avoid the leap, and apparently was enjoying the game.

During the first few weeks the lamb remains close to its mother. It usually lies down beside her when she is resting, follows her closely, or lies down only a few feet away while she feeds. In traveling, the young lamb often presses close to its mother's side, sometimes appearing to be partially under her. The lamb is near its mother except when left with other lambs, usually on a cliff, while she goes off a short distance to feed. But at such times the group of lambs is watched over by some of the ewes. So, at the time when the lamb would be most vulnerable to eagle attack, it is generally well protected, giving to the eagle little opportunity to prey on it.

Figure 35: "Come on!"

After a few weeks the lambs move about with more freedom and gambol over the meadows in little groups. Judging from their behavior, they are not greatly worried about eagles after 3 or 4 weeks. In late June and early July I have seen eagles fly low over lambs, separated from their mothers, without attempting to strike and without alarming them. Throughout the summer the eagle may occasionally dip downward at the sheep just as is does at other animals. On September 10 an eagle swooped low over two ewes and a lamb, giving them quite a start. It sailed close over them several times, calling as is passed. But after the first start the sheep seemed unafraid.

Few Lamb Remains Found at Nests.—Upon examining the vicinity of seven unoccupied eagle nests only one lamb bone was found. It was a skull which lay in slide rock some distance below the nest.

As the 13 occupied nests examined during the three summers, one old leg bone of a lamb was found below one nest and at another were the remains of two recently eaten lambs. The presence of two lambs at the one nest may have indicated that this particular pair of eagles was more inclined to attack lambs than were other eagles, or else were more fortunate in finding unprotected lambs, or possibly dead ones. One eagle was seen feeding upon a lamb which appeared to be about a week mild. As 11 of the 13 nests occupied no lamb remains, old or recent were found.

It should be pointed out that in some cases the eagle eggs do not hatch until the lambs are 3 or 4 weeks old and probably past the danger period. In these instances possibly lambs would not be taken to the nest. However, they might be brought to favorite perches near the nest where some of them would have been found if any significant number had been consumed.

During the period that the eagles are at the nest the parent birds bring to it twigs of birch, heather, or willow, probably to cover debris accumulating in it. In one nest an eagle had brought several mats of shed sheep hair, the presence of which could easily have been misconstrued as evidence of predation.

Eagle Pellets Contain Few Lamb Remains.—During each of the three summers spent on the study, substantial numbers of eagle pellets were collected from perches and nests in the lambing area. The pellets give a fairly good index of the food habits of the eagle during these 3 years. Of 632 pellets analyzed, only 6 (2 each year) contained remains of lambs. This low incidence of lamb in the eagle pellets strongly corroborates the evidence from nest examinations and general observations. The considerable information available supports the conclusion that only occasionally does an eagle feed upon a lamb. Such lambs may have been carrion or may have been killed by the eagles. If killed, they may have been healthy, weak, or deserted. In any event, whatever eagle predation exists, it is apparent that it would have no appreciable effect on the mountain sheep population.

In two recent publications dealing with the Rocky Mountain bighorn both of which have come to my attention since the above was written, no evidence was found that eagles preyed on bighorn. In a study of sheep in Wyoming (Honess and Frost, 1942, p. 56) the following statement on bighorn-golden eagle relationships is given: "To date no case of predation by eagles has been seen by a Survey member nor has one been reported for the Crystal Creek area." These eagles were living mainly on jack rabbits and ground squirrels. In a Colorado bighorn study (Spencer, 1943, p. 9) the following statement is made; "The hunting and food habits of the golden eagles in the Tarryall Mountains were observed and studied with a great deal of interest because many people consider these birds responsible for considerable predation on the bighorn sheep, especially the lambs. During the entire period of this study, not a single eagle was observed to attack or molest the bighorn sheep in any manner. The sheep were not disturbed when eagles came close so them, although the ewes were alert even when a raven came close to the lambing grounds." A study of the food habits of eagles nesting close to the lambing grounds showed that they were feeding mainly on prairie dogs. As many as seven prairie dogs were observed in the nest at one time.

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