Fauna Series No. 5

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

CHAPTER THREE:
DALL SHEEP (continued)

Migration

The movements to the summer range take place during much of June and sometimes as late as July. The return to the winter range begins in August, but most of the fall migration takes place in September. Stragglers have been seen migrating in early October.

Although many details concerning the migrations are not known, a number of observations were made of the general movements. Sheep wintering on the outside range near the Nenana River apparently summer in some of the mountains on the west side of Riley Creek. They were seen crossing to the winter range in late August at Mile 5. Some of the sheep at Savage Canyon cross a mile or more of low country and follow the ridges to the head of Savage River. Some of these sheep were seen moving southwest toward Double Mountain and others may go to Sanctuary River before going southward. Most of the sheep wintering in Teklanika and Sanctuary Canyons move south 9 or 10 miles to Double Mountain and points beyond. Some of the sheep wintering on the hills west of Big Creek go eastward to Double Mountain by way of Igloo and Cathedral Mountains. Sheep from the hills west of Sable Mountain and the head of Big Creek and possibly from lower East Fork River move eastward to Cathedral Mountain and cross the Teklanika River to Double Mountain and ridges between the forks of Teklanika River. This is a pronounced movement.

Some sheep summer at the head of the east fork of the East Fork River but I do not know where they come from. They could come from the East Fork or Toklat River winter ranges. Some of those wintering on the Toklat River move to the heads of the two forks of the Toklat 7 or 8 miles beyond the boundaries of the winter range. The few sheep on Stony Creek move to the head of the creek, and those wintering in the cliffs across from Mount Eielson move 8 or 9 miles to the vicinity of Sunshine Glacier.

Figure 21: Looking up to the head of the east branch of the Teklanika River. This is mountain sheep summer range. Vegetation, especially grass, is sparse in these mountains. [May 17, 1939.]

Before venturing a crossing over low country the sheep may spend hours looking over the region from the slopes, apparently to be sure the coast is clear. Sometimes they may spend a day or two in watching before making the attempt. Often ewes and rams move across together in a compact band.

The sheep at Sanctuary and Teklanika Canyons have 3 or 4 miles of low, rolling country to cross to reach the hills adjoining Double Mountain, their immediate destination. Three or four well-defined migration trails lead across the low country.

On June 7, 1940, a band of about 64 sheep, both ewes and rams, crossed from Sanctuary Canyon to the low hills adjoining Double Mountain. They started crossing about 2 p. m., and did not arrive at the hills until 5:30 p. m. Most of the way the sheep traveled in a compact group, stopping frequently to brook ahead. Through tall willows and scattered spruce woods they walked in single file. Just before reaching the first hills they fed for about 15 minutes on the flats at their base. They probably were all hungry and came upon some choice food. When they emerged from the woods to the open hills they were strung out considerably and galloped up the slope in high spirits, seeming relieved to have made the crossing.

On July 27, 1939, eight sheep made a belated migration from Sanctuary Canyon to the hills north of Double Mountain. From these hills I saw a group consisting of two old ewes, two lambs, and two yearlings, one 2 year-old ram, and a young ewe coming across the flats, alternately galloping and trotting, and occasionally stopping briefly to look both ahead and behind. I lost sight of them as they approached the hills to one side of me but presently I saw them cross a creek and climb a long slope to the south. They disappeared over the top but in a few minutes all eight sheep reappeared in precipitous flight and galloped down the slope with miraculous speed and abandon. The lambs kept up with the others. They passed within 30 feet of the place where I crouched in the willows so I could see clearly how they panted hard with open mouths. They climbed a slope north of me and stood above some cliffs surveying the terrain they had crossed. No pursuer was seen but it appeared they had been badly frightened. Later they regained their composure and fed and rested.

When sheep cross a valley they often follow an old rocky stream bed even though the travel would be much easier on the sod beside the stream. They probably have an instinctive feeling of safety when traveling among boulders even on level terrain since such terrain resembles the cliffs where they are safe. This instinct for seeking the boulder-strewn country on the level would serve a good purpose if such areas were extensive enough so that an enemy could not follow on firm smooth sod close by, as they can along the stream beds. On one occasion two ewes which were captured by wolves might have escaped if they had not followed a rocky stream while the wolves ran on the firm sod alongside the rocks.

In migrating along ridges where there are cliffs the sheep move leisurely, frequently stopping in places for a day or longer to feed. Sometimes they may remain on a mountain along the way for a week or more. A band of about 100 ewes and lambs fed on Igloo Mountain for a week before continuing their migration. They moved slowly around the mountain in their feeding, some days going only 300 or 400 yards. Sometimes a band will retrace its steps a half mile or so before going forward again. The movements in both spring and fall are similar. although the fall migration may at times be hurried a little by snow. However, the sheep frequently begin their fall movements before the coming of heavy snows. Single animals, or bands containing up to 100, may be seen in migration.

Figure 22: Looking southward up Igloo Creek to Sable Pass, a much-used caribou migration route. The mountains in the foreground are grazed by sheep the year around. The distant ridges are spurs of the Alaska Range. The highway can be seen along Igloo Creek (lower left). [May 17, 1939.]

The causes of migration are difficult to determine. Vegetation influences migration at least to the extent that it must be satisfactory on the range sought by the sheep. Grazing animals will often follow the snow line in spring as though they were seeking the tender new vegetation. This may be partly a cause-and-effect relationship, but, at least in part, it may be purely an incidental correlation; in following the snow line the animals may simply be driven by an urge to return to a remembered summer habitat, and not necessarily because of the seasonal stage of the plant growth. In Mount McKinley National Park it was not at all evident that the sheep were following very closely the appearance of new vegetation. Near the glaciers, where some of the sheep go, it is true the plant growth is much later than on parts of the winter range, but in many cases the growth stages of vegetation on winter and summer habitats are quite similar. On north slopes, especially, the growth on winter range is late and is green and succulent all summer. Indeed, in some respects the food on winter range seems better than on purely summer range. On winter range there is more grass and a greater variety and abundance of plant species. On the other hand, many of the species that are especially attractive to the white sheep occur on the purely summer ranges in quantity that is ample for their needs. If the migration were a complete one from winter to purely summer range, with no exceptions, one might conclude that the summer range was preferred and was not utilized in winter because of deep snows. This may still be true to some extent. A detailed study of the vegetation over all the ranges might reveal some interesting correlations.

We may assume that migratory habits had a beginning in the racial history of a species. At such an early period the sheep may have remained on the remote summer ranges until driven out by snow. Then, after such a movement had become habitual and more or less punctual, it is reasonable to assume that their fall migration might anticipate the coming of the snow. Or, the inception of the fall movement may be due to the deterioration of vegetation (by ripening and drying) on the purely summer range, for the sheep usually begin to move before the snow drives them out.

Figure 23: Excellent all-year Dall sheep range along East Fork River. [July 15, 1940.]

Insects are often stressed as a factor causing migration of big game and no doubt do at times influence local movements. Occasionally flies annoyed the sheep and caused them to seek the shade of cliffs, but usually the flies were not much in evidence, probably because of the cool breezes on the ridges. Since insects are relatively scarce on purely summer and winter ranges, it seems unlikely that any difference in their incidence would be sufficient to cause migratory movements. As suggested above, the insects might cause local movements such as from one side of a ridge to the other or from the sunshine into the shade.

One factor which may be of importance in explaining the migrations is the natural tendency of animals to wander. Let loose some horses and they will wander widely in their grazing. In any area the sheep wander about considerably over a period of days. Repeated wandering movements to certain localities may in time have established definite migration habits. In other words, the sheep may migrate simply because they like to travel.

The factors originally causing the movements of sheep may have disappeared, so that the animals may now be migratory largely because of habit which has no present-day use. When the population was excessively large, as it was in the late 1920's and often has been in the past, the sheep may have moved from an overgrazed winter range to the fresh pastures unavailable in winter. Now that there is no need for fresh pastures, the sheep may continue their treks because of a habit handed down to them.

The causes motivating sheep migration require more study and careful interpretation before any conclusions can be reached.

Continued >>>

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