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Fauna Series No. 5








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Fauna of the National Parks — No. 5
The Wolves of Mount McKinley
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WOLF (continued)

Causes of Fluctuation in Wolf Numbers

The causes of the scarcity of wolves in interior Alaska between 1916 and 1925, and perhaps some years preceding 1916, are not known. During this period of wolf scarcity the caribou herds, the main food supply, were large so that there was not a shortage of food. There was considerable trapping in the Territory at this time, but judging from the effect of trapping on the present wolf population in Alaska it is doubtful that this had much to do with the scarcity of wolves. Today there is extensive trapping in the interior of Alaska but apparently it has not caused any noticeable reduction in wolf numbers.

Intraspecific intolerance may hold a population in check but would probably not operate to cause a scarcity of the animals. If it operated at all it probably would tend to hold the animals at an optimum level which would be rather high.

The most probable cause of a drastic decimation of the wolves is disease. Mange, distemper, and rabies are some of the diseases which may affect them. Alexander Henry (1897) in his journal refers to scab in wolves. On March 5 (1801) at Pembina, N. Dak., he writes: "A large wolf came into my tent three times, and always escaped a shot. Next day, while hunting, I found him dead about a mile from the fort; he was very lean and covered with scabs."

R. M. Anderson (1938) writes as follows concerning mange in coyotes: "One young male coyote shot by Warden J. E. Stanton when the writer was with him in Cascade Valley early in September was very mangy, being so nearly devoid of hair from nose to tip of tail that the scabby and vesicular skin was plainly visible on every part of the body. Most of the half dozen coyotes seen in this area appeared to be afflicted with mange, and several wardens stated that many of the mangy coyotes lived through the winter, but that the worst cases usually died in the spring. This disease, and perhaps other causes, seems to keep the numbers down, and the reports of the superintendent of the park show that coyotes have decreased in numbers in recent years."

Warburton Pike (1892, p. 53) writes: "There was some sort of disease resembling mange among them (gray wolves) in the winter of 1889—90 which had the effect of taking off all their hair, and judging from the number of dead that were lying about, must have considerably thinned their numbers." This reference indicates that mange might destroy large numbers of wolves, especially in a large population where the conditions for the spread of the affliction would be optimum. Ernest Thompson Seton (1911, p. 351—352) says that in northern Canada mange is common at times. O. J. Murie tells me that he once lost a sled dog from mange.

Seton (1929, p. 288) says that rabies seems to break out among wolves at times. Alexander Henry (1897) as early as 1800 relates the killing of a wolf at camp which was thought to have rabies. Seton gives several instances in which wolves seemed to have had rabies. This disease probably could cause a drastic reduction in a population.

A disease like distemper could no doubt spread rapidly in a large wolf population, especially since the animals travel in packs. Distemper has been known to wipe out entire dog teams and it might affect wolves even more severely. Although the young animals are most susceptible to distemper, older wolves not having been in contact with the disease might be more vulnerable than old dogs which generally are considered immune. In 1924, O. J. Murie lost an entire dog team after he had traveled from Nenana to Hooper Bay, Alaska. Another team made up of older dogs was not affected. In that year a large number of dogs in interior Alaska are reported to have died from the disease, so apparently it was present in epizootic proportions. During April 1934, an outbreak of distemper is said to have prevailed in various sections along the Yukon and Tanana Rivers.

In an article in Field for December 1939, it is pointed out that distemper among dogs in England becomes much more prevalent and more severe in form when the dog population is high. During World War I, when few dogs were kept, there was hardly any distemper and it was nearly always mild. When the dogs were bred up again after the war, there were a great many deaths from distemper. Perhaps the disease was so destructive because the dogs came suddenly into contact with it and had no opportunity to become immunized in any degree. This occurrence suggests a possible threat to any large wolf population.

Three cases of wolves which may have died a natural death came to my attention. However, I found no evidence of disease among the wolves in Mount McKinley National Park.

The last reduction in wolf numbers may have been due to the large number of dogs that were brought into the wolf territory for transportation purposes and spread distemper or some other disease. The decrease in dog travel today may be an element favorable to the wolves. In addition, current trapping operations may be just sufficient to keep the wolf numbers from reaching a peak where they would be more susceptible to drastic reduction. This is, of course, theoretical, but seems worthy of consideration.

In connection with the problem of control of the wolf population it is of interest to consider the coyotes in Yellowstone National Park. During the long period that one or two hundred coyotes were destroyed annually in the park the coyote numbers remained high. When artificial control of the coyotes was stopped in 1935 many persons expected a great increase in their numbers. They did continue to be common, but apparently were no more plentiful than when artificial control was exercised. Now, in 1942, 7 years after control was stopped, there appears to have been a slight drop in the coyote population, judging from reports that have reached me, so that there may be fewer coyotes now than when artificial control was practiced. It is apparent that some natural controls, possibly disease, among others, are operating on these coyotes to hold their numbers in check. In a similar manner wolf numbers in Alaska may be subject to drastic natural controls and the population may again be greatly reduced through some natural factor like disease.


In Mount McKinley National Park the young of wolves apparently are born in early May. Three litters of which the approximate time of birth was known had been born in early May. According to Bailey (1926, p. 155) this is more than a month later than in the Northern States. The gestation period of about 63 days (Seton, 1929, p. 274) would place the mating season early in March. Two females in the park each had four pups, and three had six pups.

A captive female which I raised and which was later kept at Mount McKinley National Park Headquarters, did not come in heat the first year but did so in early March in her second year and was in heat about 2 weeks. This agrees with the statement by Bailey (1926, p. 155) that wolves do not breed until they are 2 years old. Another captive female owned by Mrs. Faith Hartman of Fairbanks likewise did not come in heat the first year but bred with a dog the second year. The first 2 weeks that this wolf was in heat she fought off the dog but mated each day during the third week (March 9 to March 15). The male continued to pursue her on the following 3 days but there was no further mating after the fifteenth. She whelped four pups on May 15. The first one was born at 12:30 p. m., and the others at intervals of 45 minutes to 1-1/2 hours. This observation placed the gestation period between 60 and 66 days.

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