Fauna Series No. 5

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

CHAPTER FOUR:
CARIBOU (continued)

Survival of Calves to Yearling Stage

It is difficult to learn what proportion of the calves survive to the yearling stage because not all yearlings are found with the cows. Many of them join the old bulls or the young bulls and cows. To get an accurate figure one would need a sample of a cross section of the herd and that is difficult to obtain, because many herds consist mainly of bulls and others of cows.

However, from the figures available we can perhaps get a fairly accurate idea of the percentage of yearlings. It will be noted that in 1939, in several bands, the yearlings were not classified separately from the cows. The counts for these bands have been eliminated in determining the ratio of yearlings to cows. In the bands in which yearlings were classified there were 1,727 cows and 385 yearlings. The ratio of yearlings to cows is 22 percent. Assuming that the count is a representative sample, and that the calf crop in 1938 was about the same as in the following 3 years, then it appears that a little more than half, or about 56 percent, of the calves succumbed during the first year. That, it would seem, is a satisfactory survival, although as yet we do not know how large a survival is needed to perpetuate the herd in the case of the caribou.

The figures for 1940, together with general observations, show about the same yearling ratio as was found in 1939, although the figures are meager. Ten small bands of cows were classified on May 12 with the following result: 160 cows and 34 yearlings, or a ratio of about 21 per cent. That represents a survival of about 42 percent of the calves during the year. In June and July, bands were classified which contained 213 cows and 51 yearlings, which indicates a 48 percent survival of calves to yearling age.

In 1941 the survival of yearlings seemed less than during 1939 and 1940, but not enough figures are available to substantiate this impression. Certainly among the caribou wintering around Savage River there were few yearlings. Among three or four hundred cows there were only about 20 yearlings, or a yearling ratio of only 5 or 6 percent. However, the yearling ratio for the herd was considerably higher than this figure for in bands seen later yearlings were more abundant.

There is still much to learn about the mortality of young and the numbers necessary to perpetuate a herd. Different herds, due to many variables, may require different degrees of survival among the young. In areas where there is heavy hunting by man there must be a higher survival of young to take the place of the adults shot. Under natural conditions, perhaps a much smaller survival is needed and desired. A too-high survival of young would increase the herds too rapidly, so that ranges would quickly be overgrazed. At the George Reserve near Pinckney, Mich., where some white-tailed deer were introduced in a fenced area, the survival of fawns for at least 7 or 8 years seemed to be complete. In the wild the survival of young is usually quite different. Under natural conditions a mortality of half of the young seems to be usual. However, we need more data to understand thoroughly the mechanics of wildlife population.

The number of yearling caribou, especially in 1939 and 1940 seemed adequate for the welfare of the herd when compared to the survival of yearlings in other large game animal populations.

Effect of the Wolf on the Caribou Population

It is difficult to determine the effect of the wolf on the caribou. Because the species has maintained itself through the centuries in the presence of the wolf we can expect it to continue to do so under wilderness conditions. The extensive predation on the caribou, especially on the calves, is apparently an important check on their numbers. It is not unlikely that at the present low human population level the wolves serve as a useful cheek on the caribou. If this check were entirely removed the caribou might increase in numbers to such an extent that vast areas of choice lichen range would be severely damaged. Those familiar with the overuse of many big game ranges in the States can readily appreciate the importance of this consideration.

In localities where hunting by man becomes extensive enough to be an important check on the caribou, as it may be in some parts of Alaska, some adjustment in wolf numbers may then be necessary to offset the reduction caused by man. Present information on these details is meager so that it is difficult to decide on management practices. But if man's hunting under the present wilderness conditions that exist over large parts of Alaska is insufficient to keep the caribou in check, then the value of the wolf in this respect should not be overlooked.

The effects of the wolf on the character of the caribou over a long period are also hard to evaluate. The wolves may be an important evolutionary force in changing or maintaining the caribou characteristics.

The Mount McKinley National Park herds appear to have held their own during the last 20 years. Although there has been heavy wolf predation in recent years, the caribou seem to be adjusted to withstand the losses. To care properly for the caribou herds and insure their perpetuation, regular observations should be continued so that their status, together with that of the range, may be known at all times.

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