Fauna Series No. 4

Fauna of the National Parks — No. 4 Ecology of the Coyote in the Yellowstone

CHAPTER VI:
MULE DEER IN RELATION TO COYOTES

DEER MORTALITY, WINTER OF 1937-38

IN the course of the field work carried on during November 1937, and from January 11, 1938, to June 1938, 57 dead deer were recorded. Three of these deer were still alive when found but were in such a weak state that I was able to catch them and perform autopsies.

Sex and age of dead deer.—In order to learn what part of the population sustained the greatest winter mortality, the age and sex of dead deer were recorded when the information could be obtained. Since the sex of most of the fawns was not determinable, this has not been tabulated for any of them. The 57 dead deer were classified as follows: 2, sex and age not known; 9 bucks (6 very old, 3 in their prime); 5 old does; 3 yearlings (2 males, 1 female); 38 fawns.

Figure 20— The opened mouth of a fawn deer showing some of the 52 nose fly larvae found in gular pouch and throat. It had died from some cause other than predation.
Tower Falls, April 15, 1938.

As we would expect under adverse conditions, the highest mortality was among the fawns and the old animals. It is significant that among the elk, which are preyed upon little or not at all by any predators during the winter, the heavy mortality likewise falls among the calves and the old-age group. It is, therefore, apparent that the weak animals die during the winter, regardless of the activities of predators.

Mortality by months.—The does and fawns, and the bucks to a lesser degree, approach the winter in good flesh. The rigors of winter gradually reduce the stamina of the animals, the rate of reduction depending upon the condition of the range and the severity of the winter, especially the condition of the snow. If the winter is severe the weaker animals begin to die as their vitality is sapped. Many may live until late winter and early spring before succumbing. Most of the population usually survives and recuperates with the advent of the new spring forage. Diseases such as necrotic stomatitis may kill off some animals in good flesh and possibly predators may take a few strong animals, so that all winter deaths are not necessarily due to malnutrition. It must be remembered, however, that malnutrition is often the fundamental cause of mortality brought about by other agents.

The number of dead deer found during each month is as follows: November 1937, 2; December 1937 (no observations made but apparently mortality light); January 1938, 9; February 1938, 12; March 1938, 15 (one poached in March not tabulated); April 1938, 17; and May 1938, 1.

The figures are too small to be conclusive but some correlations appear which are at least suggestive. The winter range along the Yellowstone River between Deckers Flat and Tower Falls is decidedly poorer than the range between Lava Creek and Reese Creek, and the difference was accentuated in 1937—38 by heavily crusted snow, as explained elsewhere. A tabulation of the deaths, according to months, for each of the two ranges, follows:

The low figure for the dead deer found along the Yellowstone River in February does not give the true picture for it was obvious that 7 of 9 deer found on this range on the 4th, 5th, and 6th of March had died in February so that the figure for the Yellowstone River range should actually be 11 deer for February and 3 for March. The correlation to which I wish to call attention is an early relatively high mortality in the more severe range along the Yellowstone River and a late relatively high mortality on the more favorable winter range between Lava Creek and Reese Creek. The figures indicate that the mortality began earlier on the poorer range and dropped considerably in late March and April. By the time these latter months had been reached most of the susceptible deer (the fawns) had succumbed on the poor range. On the other hand, mortality on the better range did not begin until later, when the vitality of the animals had been gradually reduced, thus resulting in a late winter mortality. If the coyote preys extensively on strong healthy fawns, the correlation pointed out is not so significant for there were some early coyote kills along the Yellowstone River. There is, however, some evidence as will be pointed out elsewhere, that strong fawns may not be highly susceptible to coyote predation. In reviewing these figures it must be remembered that there is a good deal of chance connected with the finding of the carcasses and that consequently dates of discovery of the carcasses may not be a true index of the time the animals died. My general impression from observing the condition of the deer and the range conditions during the winter, however, is that the above correlation, showing a higher early mortality on the poorer range, is a true picture of the course of events.

Figure 21— An old doe after a hard winter. This animal was drooling, had a lump on the jaw, and was apparently sick beyond recovery.
Tower Falls, April 28, 1938.

Causes of winter mortality.—Autopsies were made, when possible, but in many cases insufficient remains were present to give indication of even a generic cause of death. Early in the winter most carcasses were rapidly cleaned up by coyotes so that it was difficult to determine the animals that had been killed by them and those which had died from other causes. Later in the winter, carcasses were not cleaned up so quickly and there was then some evidence to account for death in a general way. Before discussing in further detail the various causes of mortality it might be well to give the following summary: Malnutrition and disease: 1 buck, 2 yearlings, 9 fawns; old age: 6 bucks, 4 does; coyote predation: 8 fawns; fractured leg: 1 yearling, 1 doe, 1 young buck; fighting: 1 buck; struck by car: 1 fawn; run down and killed by myself for examination: 1 fawn; killed by poacher: 1 fawn. The cause of death of 18 fawns and 2 deer of unknown age and sex could not be determined because only fragmentary remains were present. Death may have been due to coyote predation, disease, malnutrition, or a combination of factors.

When it was evident that coyotes had not killed the deer and that the latter were not aged, death was attributed to malnutrition or disease. Coyote predation as a cause of death of fawns was ruled out when the carcasses were slightly eaten, or untouched, with no evidence of coyote tooth marks. All but four such carcasses were found in April when carrion became abundant because of the many dead elk. Three of the fawns and one yearling were seen on the Yellowstone River range. One yearling had several sores in the mouth indicating presence of necrotic stomatitis. A young buck in his prime which had died on February 8 had a malformed antler which suggested that the animal had been ailing for a long time. All the animals found dead were extremely thin, indicating that malnutrition may have been a primary cause of death in many cases. Although the death of a fawn, discussed elsewhere under the section dealing with coyote kills, was caused by either a car or coyotes, I have attributed it primarily to mechanical obstruction of the nasal passages by 102 nose-fly larvae. Such larvae were discovered in 10 of 21 carcasses in which an examination for them was possible. The larvae were usually found in the gular pouch; in two cases the pouch was completely filled, 52 being found in one case and 51 in another. The 102 larvae in the fawn on February 20 were nearly all about an inch long; 50 in a buck on April 21 were mostly one-half inch or smaller in size, but a few an inch long were also present.

Rush (1932) has reported on 37 post mortems performed on deer in Yellowstone during the years 1929 to 1932, inclusive. The cause of many of the deaths was either directly or indirectly attributed to the presence of botfly larvae, lungworm, lesions due to feeding on foxtail, tapeworms and roundworms, and inflammation of stomach due to overfeeding on cottonseed cake. Of the 37 animals autopsied, 2 deaths were attributed to the coyote, 13 to disease and parasites, 11 were sick and slaughtered for autopsy, 8 were killed and injured accidentally, 2 died from cottonseed eaten too generously, and 2 died from eating garbage. Twenty-nine of the thirty-seven deer were fawns.

I found 6 bucks and 4 does which undoubtedly had died primarily from old age. The animals were very thin and the teeth were worn to the gums and some were missing. Two of these animals were noted before they expired, too weak to rise. Two died in January, 2 in February, 1 in March, 4 in April, and 1 in May. Several extremely thin old animals seen in late April were undoubtedly not far from death. A hard winter probably causes some of the old animals to succumb a year or so earlier than they would under favorable winter conditions.

Tracks in the snow indicated that 8 fawns had been killed by coyotes. These incidents will be described in some detail in a later section. There was no evidence that the coyotes molested any deer except fawns.

A young buck with a broken humerus was killed by a ranger. It is likely that the bone was fractured by a shot or possibly by a fall or collision with a car. The animal was in poor condition. On a steep slope along the Yellowstone River an old doe was found with a double fracture below the calcaneum. Below the breaks the leg was bloodshot; it was evident that the animal had been alive for a time after the accident. There was very little food in the stomach so it had apparently been down for a time before dying. At the foot of a steep slope near Crevice Lake a dead yearling with a hind leg broken a little above the dew claws was found. The leg was swollen below the break. In traveling, especially over talus which in many places along the Yellowstone consists of sharp blocks, one would expect that a broken leg would not be a rare occurrence. Deer were frequently seen limping. Ranger Gammill in his monthly report for January 1935 mentions seeing a doe at the Hellroaring Station during the month with a front leg broken below the "ankle." The leg seemed to be mending, but in a crooked position.

Figure 22— Two mule deer. A battle such as this one occasionally results in carrion for coyotes.
Terrace Mountain, September 29, 1937.

A buck was killed in a fight on November 13, 1937. When retreating from its adversary it had been hooked on the inside of the left hind leg. The mortal wound had been made by a tine which pierced the abdominal wall and severed an artery under the backbone. Deaths resulting from fighting are probably rather rare. Assistant Park Naturalist Oberhansley saw a buck killed in a fight in the park, and Ranger Condon saw two bucks with locked antlers which did not break loose for at least an hour. One of the animals was quite exhausted.

One deer was known to have been killed by a car. Such accidents are occasional.

One of two weak fawns, on March 19, was run down after a rather short chase and killed as it lay on the slope completely exhausted. This fawn probably should be classified as dying from malnutrition or disease for certainly it was too feeble to survive. Three other extremely weak fawns were noted. This incident will be discussed later.

The legs and head of a fawn were found near Bear Creek just outside the park. No doubt deer wandering beyond the park boundaries are occasionally taken illegally. At Deckers Flat, adjacent to the park, during the elk hunting season more than 60 deer were reported shot illegally and some persons thought the figure much higher. Some of the deer in this locality spend part of the time within the park boundaries.

Mortality among the deer varies from year to year, depending on various factors. Ranger Rudolf Grimm, during the winter of 1935—36, found more than 30 deer which had died from disease in a restricted area on the Game Ranch. A trapper told Ine that during the same winter many deer had died in the Gardine-Jardine area.

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