A FIELD STUDY of the wolf-Dall sheep relationships in Mount McKinley National Park was begun in April 1939, and was terminated in August 1941. Other animals included in the study are the caribou, moose, grizzly, fox, and eagle.
For several years preceding 1926, wolves were scarce in the park. Their noticeable increase in 1927 and 1928 coincided with a general increase of wolf numbers in interior Alaska. From about 1928 to 1941, wolves have been common in the park as well as over interior Alaska, and apparently their numbers have not varied much in the park during this period. It is not unlikely that the fluctuations in wolf numbers are due to diseases such as distemper, rabies, and mange.
A wolf family at a den on East Fork River was closely observed during two denning seasons. In 1940 there were five adult wolves at the denthe parents, two males, and a female. After these animals left the den, two other males joined them. In 1941 the den was occupied by the same pair; the second female mated with one of the extra males and had her own den. She later brought her pups to the original den and the two families lived together. The wolves generally rested at the den during the day and hunted at night, but some hunting was also done during the day. Food was brought to the den by the parents and the other adults. The wolves were unusually friendly among themselves, and the pups played with all the adults.
The 1940 group of seven adults and five pups traveled together during the fall and winter. They were last seen together on March 17, 1941. None of the 1940 young was observed at the 1941 den. They traveled readily over a home range known to be at least 50 miles in diameter.
Two other wolf families were observed. In one of these there were three adults with the pups.
A wolf pup which was raised in captivity became tame and friendly. It did not come in heat until it was almost 2 years old. Another captive female wolf crossed with a dog and had young when she was 2 years old.
The feeding habits of the wolves were determined by field observations and the analysis of 1,174 scats. The principal food was caribou and mountain sheep, but ground squirrels, marmots, and mice were sometimes utilized to an important extent. Snowshoe hares were scarce, so there was no opportunity to learn the extent to which, when plentiful, they furnish food for wolves.
An exceptionally large Dall sheep population was greatly reduced by starvation during the winters of 1929 and 1932 because of the deep and crusted snow conditions. No doubt there was also heavy wolf predation at that time. Since 1932 the sheep population appears to have been rather stable.
The sheep breed in the latter half of November and early December, and the young are usually born in May. A single lamb is the rule.
Part of the sheep population migrates to a summer range near the main crest of the Alaska Range, but many sheep remain on the winter ranges all year. Migrations to and from the summer range take place in early summer and early fall. Grass is the staple food the year round, but much willow and a variety of herbs are eaten, especially in summer.
A disease which appears to be actinomycosis is common among the sheep. A heavy infestation of lungworm was found in one yearling.
The lynx is a casual predator on the sheep and has little effect on their numbers. The effect of the golden eagle on the sheep is unimportant.
The wolf preys extensively on sheep. Several hunting incidents are described. Wolves apparently chase many sheep before they find one that they can catch. Artificial intrusions such as roads increase predation.
To determine the types of sheep killed by wolves, sheep skulls were collected. These skulls were classified into four groups as follows: lamb, yearling, prime (2 to 8 years), and old (9 years and older). The skull studies showed that very few sheep in the 2- to 8-year class died, and that the majority of casualties in this class were severely diseased. The largest number of skulls belonged to the old-age group. There was a heavy mortality among young sheep in their first winter. Because so few sheep died in their prime, it is obvious that any wolf predation affects mainly the weaker animals.
The wolves restrict the sheep to the rougher country. It appears that during the period from 1932 to 1941 the sheep population was held in check by the wolves. It is the predation on the yearlings which seems to be most important in controlling sheep numbers.
During three seasons, counts were made of the lambs, yearlings, and ewes. In 1939 there was a large lamb crop and a large survival of yearlings from the 1938 lamb crop. The 1940 counts showed a heavy winter mortality in the 1939 lamb crop and an extremely small lamb crop. In 1941 yearlings were scarce, but the lamb crop was large. A 50-percent lamb-ewe ratio (2-year-old ewes classified as adult ewes) appears to constitute a good lamb crop. A survival of 50 percent of these lambs to the yearling stage probably is sufficient to increase the population. The summer losses among lambs were extremely light. These classified counts showed that during some years the survival of lambs is so small that there is a drop in the population.
Wolf predation probably has a salutary effect on the sheep as a species. At the present time it appears that the sheep and wolves may be in equilibrium.
A herd of caribou numbering from 20,000 to 30,000 live in Mount McKinley National Park and adjacent regions. They make annual migrations which may vary in minor or major particulars from year to year. They breed in late September and during most of October and the calves are born about the middle of May. Wolves feed extensively on the calves which, when available, constitute the main food supply. Several hunts are described in detail. The calves are captured in open chase. Usually the victim is one of the calves which drops behind the others, so that it appears that the weaker animals are eliminated by the wolf. Adult caribou are also run down, but when the calves are young the adults are seldom taken. In interior Alaska the caribou furnishes the main food of the wolf. When caribou are in the vicinity of sheep hills they are a buffer between the wolves and the sheep, thus materially reducing the wolf predation on sheep.
The caribou are subject to attack by the warble fly and the nostril fly; they also appear to suffer from actinomycosis.
About half of the cows above yearling age are followed by calves. In 1939 the yearling-cow ratio was 22 percent, signifying a loss during the first year of about 50 percent. In 1940 and 1941 the counts indicated similar losses of calves during the first year.
Under natural conditions the caribou herds are no doubt adjusted to the presence and pressure of the wolf.
Moose are common in suitable habitat. Their principal food at all seasons is willow. The rut begins in early September and continues for 3 or 4 weeks. The young are born in late May. Twins are common. In the presence of a large wolf population in recent years, moose have increased in the park and the region adjacent. The moose range is in good condition.
The grizzly bear is common in Mount McKinley National Park. Its food habits were studied by analyzing 201 scats and making numerous observations of feeding grizzlies. The food habits change as the seasons progress. In May and early June the principal food consists of roots; during most of June and July the main food is grass (mainly Calomogrostis langsdorfi), and Equisetum arvense; during late July, August, and September, blueberries and other berries make up the bulk of the food. Ground squirrels form a small part of the food at all seasons, and carrion is always acceptable. Grizzlies were seen feeding on caribou calves but probably are unable to catch the calves after they are a few days old. The bears mate during May and June, not oftener than every 2 years.
Some bears confined their movements to a rather definite range. One female was generally found in an area about 9 miles in diameter. There was considerable overlapping of ranges. The grizzlies frequently rob the wolves of their kills. Once a family invaded the vicinity of a wolf den in search of food scraps. The wolf will attack the grizzly but is unable to close in on him.
Foxes flourished despite the presence of wolves. No evidence was found in Mount McKinley National Park to show that wolves are harmful to foxes. In the fox-wolf interrelations the fox may be the gainer since the wolf often makes food available to him. Adult foxes have a year-long home range. The food habits were studied by analyzing 662 summer scats and 124 winter scats. The principal summer foods were mice and ground squirrels, and the principal winter foods were mice and blueberries. The snowshoe hare was rare so was scarcely available to the foxes.
The food habits of the golden eagle were studied by making observations at 13 occupied and 13 unoccupied nests, and by an analysis of 632 eagle pellets. The main food of the eagle is the ground squirrel which was found in 86 percent of the pellets. Most of the calf caribou eaten was carrion. The predation of the golden eagle on Dall sheep lambs and on the fox appears to be negligible. The economic status of the eagle was found to be favorable.