NATIONAL PARK SERVICE Fauna of the National Parks of the United States No. 4 Ecology of the Coyote in the Yellowstone

BECAUSE fear had been expressed that coyote depredations on mule deer (Odocoileus hemionus macrotis), especially in winter, were so extensive that the future of the species in Yellowstone was threatened, I devoted much of my time during the winter of 1937-38 to a study of factors affecting the deer. Their food habits were studied in considerable detail, their range was carefully examined, competition of other ungulates noted, condition of deer watched, fatalities recorded and their causes and the age and sex of the dead animals determined when possible. Fawn survival through the winter was tabulated, coyote depredations noted, and general relationship between deer and coyotes was observed. Since the status of several other species was also involved and had to be studied, time did not permit me to go into details to the extent desired.

Figure 16— Browse line on Douglas fir along the Yellowstone River above Blacktail Deer Creek: a typical condition marking this a poor deer range.
March 21, 1938.

WINTER RANGE

MOST of the deer winter on the north side of the park in the following localities: Reese Creek, Game Ranch, lower reaches of the Gardiner River and Lava Creek, and along the Yellowstone River from Gardiner to Tower Falls. A few deer are found at Old Faithful, Norris, and occasionally at other isolated spots such as Cache Creek and Canyon. In 1937-38 deer were absent from some areas around Hellroaring Creek where they had wintered the previous year. The heavy crust on the snow in 1937-38 no doubt tended to restrict the winter range while the loose snow in the winter of 1936-37 had permitted the deer to spread out more freely. The deer move from the interior of the park to the winter range in the latter part of November and return in late May.

DEER AS COYOTE FOOD

DURING the winter, deer (in the form of carrion) furnish a varying supply of food for the coyotes. In some years rather heavy mortality among deer due to malnutrition and disease has been reported, while in other years the mortality has been light. In the latter part of the winter some fawns, chiefly the weaker ones, are killed by coyotes. Deer remains were found in 64 droppings gathered between March and November but many droppings noted in winter which were not recorded contained deer hair.

Figure 17— The Gardiner River, a short distance below Lava Creek. This area has a heavy winter population of deer. Cottonwoods and fir in the bottom: sage brush on the slopes.
March 25, 1938.

GENERAL CONDITION OF DEER, WINTER OF 1937-38

WILD populations are heir to a variety of ailments; they are subject to parasites, diseases, accidental crippling, and general debility due to old age, or malnutrition resulting from unfavorable winter range. The extent to which a population is affected has, of course, a direct bearing on the amount of carrion which may be available to flesh eaters, and probably also has a bearing on the extent of predation. So before tabulating the dead deer which were found I feel it worth while to give a general picture of the health of the deer by listing observations which were made during the winter of 1937—38.

Because conditions were specially unfavorable to deer over part of the range in the winter of 1937—38 as a result of crusted snow, the condition of the deer was perhaps worse than usual. By spring they were all poor. Fawns, especially, became thin and weak, and some of the aged animals lost flesh until the skin hung closely to the skeleton.

Figure 18— A thin, weak fawn which probably succumbed before summer.
Near Mammoth Springs, March 29, 1938.

     1937

     1938

Figure 19— Fawn deer reaching for sagebrush twigs exposed during a thaw.
The sagebrush in this area was heavily browsed.
Gardiner River, March 25, 1938.

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.

FAWN SURVIVAL

An effort was made to determine the number of fawns which were surviving in order to learn: (1) The status of the deer population, that is, whether it appeared that enough fawns were surviving to maintain the species; and (2) if there were any correlation between the condition of a unit of the range and the number of fawns surviving on it.

After the deer had moved into the winter range in 1937—38 there was no noticeable shifting about from one unit of the range to another, even though there is continuous winter range between some of the units. On the contrary, the deer seemed restricted to relatively small areas. Approximately the same number of deer were always found in certain draws, and individual deer that I could recognize were found frequently in the same locality. For instance, a horned doe remained in the vicinity of Junction Butte the year round. She was seen there by Ranger Condon in the winter of 1936—37, and in the fall of 1937, early spring of 1938, and early spring of 1939 by myself. On February 5, 1938, near the mouth of Blacktail Deer Creek I saw a doe with the top half of both ears missing. Ranger Gammill saw this doe in the same area on March 28 almost 2 months later. Six counts of deer in the open areas below Deckers Flat between February 17 and April 1 varied from 40 to 48, indicating a stable population. These deer were usually concentrated around two draws a few hundred yards apart. During most of the winter the home range of some of the deer probably did not cover an area much more than a mile across, others possibly ranged more widely. The deer tabulated for the various units on the winter range were on the whole restricted to that particular unit all winter. Any movement that there might have been would not be sufficient to make an appreciable difference in the figures.

At first some attempt was made to segregate the yearlings but as differentiating them was difficult and often there was not time to classify them, they were finally grouped with does and bucks. All the animals were classified into three groups, does (including yearling does) bucks, and fawns. The fawns were usually readily distinguishable by a combination of characters, including small size, short rostrum, marked facial pattern, and general darker color, but by spring some of these characters were not so distinctive and occasionally a few animals were seen which had to be scrutinized carefully to determine their age. Size as a criterion is deceptive so that yearling does sometimes appeared to be adults and in the distance yearlings sometimes looked like fawns. After some experience with the difficulties involved the likelihood of errors in making fawn identifications became small.

Figure 23— Buck deer killed by another buck during the rut. It was wounded inside the hind leg and in the abdominal cavity where a tine apparently pierced an artery near the vertebrae.
Game Ranch, November 13, 1937.

Because some of the bucks spend the winter higher than the does, in the deeper snow and among the trees on the fringes of the winter range where they are not so easily counted, it is certain that the bucks are not represented in the counts in their true proportions. But even after making a most generous allowance for uncounted bucks there still seemed to be about twice as many females as males in the population. The lower number of bucks may be due in part to the fact that bucks enter the winter in poor condition from rutting activities. Fighting, resulting in a few casualties among the bucks and possibly a number of injuries which have some permanent weakening effect, may be a minor factor in reducing the buck population.

Since figures for the fawn-doe ratios on the different range units are comparable, percentage of fawn increase is given in terms of the doe counts. Buck counts are not included in these calculations because of their probable variability over the various range units. The tabulations made in the winter of 1937—38 are based on a sample which includes more than 800 of the 1,000 or more deer on the winter range. Because there is sometimes considerable variation in the fawn ratio in various bands, small samples are apt to be misleading.

Winter of 1936—37.—My data on the survival of fawns during the winter of 1936—37 are not extensive but bear out observations made by others. On May 7, 1937, before deer had begun to leave their winter ranges, I observed along the Yellowstone River between Hellroaring Creek and the mouth of Blacktail Deer Creek 10 does and 8 fawns. The percentage of fawns in the sample of the population seen may have been considerably higher than the true average but indicated a good winter survival. This was on poor range where, in the following hard winter of 1937—38, scarcely a fawn survived. Ranger Raymond West, who spent some time in the area during the winter, observed that nearly every doe was followed by a fawn. Ranger Dave Condon, who watched deer closely at Tower Falls, also reported a high fawn survival. During the entire winter of 1936—37 the snow was loose and crustless, a condition highly favorable to the deer, especially on the poor range along the Yellowstone River where the different species of food plants are quite scattered and so entail for the deer considerable moving about to obtain a balanced diet.

Winter of 1937—38.—The winter range was divided into a number of more or less natural units, between which there was very little movement of deer. Counts of deer on these units were made as opportunity offered throughout the winter. The classified counts and the fawn-doe ratio have been tabulated. The counts on each unit of range vary considerably because the deer were not always where they were visible to the same degree, and because it was not always possible to cover the entire unit. In some areas the number of deer seen differed considerably. Especially was this true along parts of the Yellowstone River where the numbers of deer seen in a stretch on different trips varied from 1 to more than 100. The great variation in counts on this range was due to the fact that most of the inhabited part of it was wooded so the deer were not readily seen but, as snow left the open areas, some deer came out on them to feed and were easily observed.

Classified Counts Made in 1937—38 in Different Range Units

Best late counts excerpted from classified counts

1 Adults.

Figure 24— Part of a band of deer which included 3 fawns, wintering near Norris.
April 29, 1938.

LOSS OF FAWNS

Losses during winter of 1937—38.—The latest large counts for the different range units have been placed in one table for convenience. See page 72. Most of these counts were made in April, many late in that month. Limited fawn losses probably occurred after some of these counts were made, but on the whole the figures for the fawns are close to the proportion that came through the winter. Since these counts probably represent about 75 per cent of the population, the numbers of fawns and does in the counts are not far from the actual numbers on the ranges.

The total of the late counts made over the main range units is 485 does, 174 fawns, 136 bucks, and 41 deer unidentified. The fawn-doe ratio in these counts is 35 percent. The percentage increase over the doe and buck populations combined is 28 percent. It is known that relatively fewer bucks than does are counted, so to be really conservative the number of bucks might be doubled. Then the increase in the herd due to the fawn crop becomes about 22 percent. This includes the population along the Yellowstone River where scarcely any fawns survived, so it appears that there was a healthy increase in the deer population as a whole, even though the winter over part of the range was more severe than usual.

Since large counts of deer were not secured when they first came to the winter range and therefore some mortality had already occurred when the first extensive counts were made in January, figures are not available which would give a good clue to the actual loss of fawns during the winter. Counts made in January (one) and in February total 355 does and 176 fawns for Reese Creek, the Game Ranch, along Gardiner River and Lava Creek, below Deckers Flat, between Deckers Flat and Blacktail Deer Creek, and between Blacktail Deer Creek and Little Cottonwood Creek. Counts made in March (one) and in April on the same ranges total 424 does and 148 fawns. If the early fawn ratio was true for the whole population, then the April count shows a loss of 62 fawns or 29 percent of the fawns since February. There was, of course, considerable loss previous to the February counts, especially on the Yellowstone River range. There fore the actual winter loss of fawns was much higher than 29 percent, being almost 100 percent along the Yellowstone River.

Figure 25— The two fawns on the left side are feeding on greasewood (Sarcobatus).
Much of the heavily browsed sagebrush has been killed.
Slope near Gardiner River, March 25, 1938.

Fawn mortality higher than doe mortality.—In practically all of the areas there was a downward trend in the ratio of fawns to does. Where the mortality was not so heavy this differential mortality was not great, but along the Yellowstone River, where the mortality was drastic, the ratio dropped almost to zero.

Fawn—Doe Ratio, Winter of 1937—38

Fawn mortality correlated with winter range conditions.—The Reese Creek, Game Ranch, and Gardiner River-Lava Creek winter ranges, and that below Deckers Flat, are not very different in quality, but the first named is the best of the three, being the least overbrowsed. The Game Ranch range I would rate as slightly superior to the Gardiner River-Lava Creek range because of the greater availability of Douglas fir browse, and the range below Deckers Flat is similar to the others in quality. The differences between these ranges are hardly large enough to expect a corresponding difference in fawn survival, but the last deer counts on three of these ranges showed a correlation of range quality and fawn survival, the ratios being 42 percent for Reese Creek, 41 percent for the Game Ranch, and 38 percent for the Gardiner River-Lava Creek area. The range below Deckers Flat had a fawn—doe ratio of 60 percent but this was higher than usual because of a low count of does so that 47 percent is probably a much better figure. The differences in the fawn ratios are too small to be of any significance. What is significant is the similarity of fawn survival on these rather similar ranges.

The range along the Yellowstone River above Deckers Flat was a strikingly inferior and less favorable winter range than the previously mentioned four ranges, because of severe overbrowsing, scattered distribution of food plants, and especially crusted snow. On the section between Deckers Flat and Blacktail Deer Creek a rather small count made on March 21 showed a 2-percent faw-doe ratio and as some mortality resulted after this date, survival on this range was undoubtedly very low.

On the section of this range between Blacktail Deer Creek and Little Cottonwood Creek 72 does and 11 fawns were counted on February 16, 88 does and 13 fawns on March 5, and 63 does and 2 fawns on April 26. The survival of fawns on this range was almost nil. Apparently a good fawn crop arrived on this range but heavy losses commenced in January. Between Hellroaring and Tower Falls, a range covered with crusted snow, the survival of fawns was also low. On April 2, I counted 9 does and 1 fawn, the latter appearing to be very weak. The correlation of the fawn survival and condition of the winter ranges was very pronounced in the winter of 1937—38.

Losses during winter of 1938—39.—In the fall of 1938 deer were observed between November 11 and November 23 but during this period only a few of the deer had returned to the winter range so the counts were not entirely representative. The following counts suggest that a fairly large proportion of fawns arrived on the winter range. The faw-doe ratio of the total number recorded is 83.

In the spring of 1939 the following deer counts were made but the samples were too small to give the full picture:

The fawn-doe ratio of all counts combined is 26, a lower ratio than existed during the winter of 1937—38. The figures are too incomplete to make detailed comparisons with those of the previous winter. Fawn survival apparently was extremely low in the winter of 1938—39 along the Yellowstone River from Hellroaring to Deckers Flat, just as it was in the winter of 1937—38. The fawn-doe ratios on the other ranges, except at Tower Falls, were lower in the winter of 1938—39 than in the previous year although more complete counts might have shown less difference. In 1938—39 there was more snow over parts of the deer ranges in the Reese Creek, Game Ranch, and Gardiner River sections. This additional snow, along with continued deterioration of the range, may have been a factor in the apparent lower fawn survival that winter over the above-named deer ranges, but more complete counts and closer observation would be necessary for certainty.

Along the Gardiner River on February 26, 1939, I noted two carcasses of deer, one cleaned and the other partly eaten by four coyotes. One carcass was that of an old buck, the other of an old doe with teeth worn to the gums. Ranger Grimm found remains of three adult bucks in the Reese Creek area which apparently had died from wounds received during the hunting season. No bucks were seen on Reese Creek near the edge of the park adjacent to the area where considerable hunting took place the previous fall. The apparent scarcity of bucks in this region may be due to this drain.

On March 5, 1939, hair remains of two deer were found near Blacktail Deer Creek and Crevice Creek and the mandible of a fawn below Crevice Creek. The general impression received in walking from Hellroaring Creek to Gardiner along the Yellowstone River was that deer were as numerous as during the winter of 1937—38. They occupied a somewhat wider range, being found near Hellroaring cabin where they were not found in the winter of 1937—38. The fawn increase in 1939 is apparently sufficiently large to maintain or possibly increase the deer population in the park.

Fawns killed by coyotes on the winter range.—Although healthy adult deer do not seem to be subject to coyote predation, it appears that fawns are occasionally killed by coyotes on the winter range. Tracks in the snow near fawn remains indicated in several instances that the fawns had been killed by coyotes. Since our knowledge of the circumstances under which prey is killed by predators is scant, it seems desirable to give the evidence found at carcasses which showed indications that coyotes had made the kill.

Figure 26— Cedar with low branches heavily browsed.
The deer, a cripple, was left behind while 5 others ran at observer's approach.
Gardiner River, January 16, 1938.

     1938

COYOTE METHOD OF HUNTING FAWNS

I did not have the good fortune to observe the coyotes in the act of hunting a fawn but have heard many persons state that coyotes systematically chase deer down the slopes and catch them at the bottom. Along the Yellowstone River it has been said that deer have been driven down to the river where other coyotes were waiting to help finish them.

On March 19, along the Yellowstone River below Crevice Creek I had an experience with some deer which may be significant in explaining coyote predation on fawns. Fresh deer tracks in the snow crossed the trail and I followed them up the slope on the chance of seeing the deer and getting a count of the fawns. I had gone but 200 yards or so when I came upon 14 deer, 5 of which I classified as fawns. My observation was hasty for the deer ran off on seeing me, and since the fawn proportion was unusually high, I followed in order to check my count. I again saw the deer crossing a steep open rocky slope but several passed out of sight into a draw before I could get a full count. I noted two fawns that appeared tired, lagging 25 or 30 yards behind the others. At the edge of the draw I found the band of deer only 30 or 40 yards away. They hurried quickly up the steep slope, all except the two fawns behind. One of these kept on, but the other stalled. I hurried upward toward it. After a brief rest it was able to climb a little farther but again stopped, trying to climb but too weak to do so. Another brief rest and it walked forward a few yards more and lay down in a hiding posture with head and neck stretched forward and held close to the ground. I continued to hurry up the steep slope in order not to give the fawn too much time to recuperate. When I was within a few feet it rose, and, finding climbing too difficult, followed a contour of the slope instead. I tried to keep directly below it to force it upward, thinking that if it started down the slope it might be able to run away from me. However, it got ahead in spite of my efforts and swung around down the slope. When it had made four or five creditable jumps I thought it was going to run away. But its legs buckled on the last jump and it went down in a heap, rolling over several times before coming to a stop. It gained its feet before I caught up with it, but after a few more jumps it fell again, rolling and sliding several yards to a stop. It lay perfectly relaxed with its head in a crack between two rocks. I photographed it, and while I was changing film it managed to take two or three more jumps before falling and rolling again. Now it lay utterly exhausted, not even twitching a muscle when handled.

An autopsy revealed clear lungs and liver, and an absence of nosefly larvae. There were a moderate number of ticks, especially on the neck. The animal, a female, was very thin. It was drooling a little but this may have been due to overexertion.

I wondered if I had staged a hunt similar in many details to a coyote hunt. Possibly the coyote harasses a band of deer on the chance of finding a weak animal. The herd moves up the hill and the weak fawns are left behind. Lacking strength to run up hill the fawn runs down the slope. This may explain why most chases are downhill. His weakness causes him to stumble or slip in the rough steep terrain since considerable strength is necessary to brace himself in landing at the end of each downhill jump. The fawn when killed by coyotes may at times be lying utterly exhausted. This is speculative, of course, but seems permissible because of the similarity between my observation of tracks of fawns presumably killed by coyotes and my own "hunt." That there are many weak and ailing fawns during the winter is unquestionable.

Figure 27— Weak deer fawn which was followed by the writer until it collapsed as shown.
The incident is described in the section "coyote method of hunting fawns."
"Crevice Creek, March 19, 1938.

These data have been given elsewhere, but I might mention here that on the day the above observation was made, besides the second weak fawn in the band I was following, one was seen across the Yellowstone River so weak that it was tottering and stumbling. On March 5 another very thin fawn was seen alone, probably left behind when the band moved on, and on April 1 a lone weak fawn was seen.

On February 12, 1938, I witnessed an incident in which the coyotes seemed to be watching a deer herd, possibly seeking an animal that they could run down. All day the air was full of snow and a strong wind was drifting the snow along in swirls, so that tracking was almost impossible and visibility was poor. A half mile above the mouth of Lava Creek I saw, about 1 p. m., a band of deer that had sought the shelter of a grove of firs some distance up the slope of Mount Everts. Three or four hundred yards farther along two coyotes crossed the trail ahead of me and ran up the slope in the general direction of the deer. About a quarter mile further along I met three more coyotes coming out of the creek bottom. They also climbed the slope of Mount Everts, stopping occasionally to watch me.

About 2 hours later when returning I happened to look behind and saw a deer bounding down the slope of Mount Everts to the creek bottom and up on the other slope. The deer appeared to be a yearling doe. I waited a few minutes to see if she was being chased, and then after following her trail for a time back-tracked her up the slope of Everts. The drifting snow made it difficult to keep on the trail but I managed to follow the widely spaced tracks to one of the scattered clumps of trees high up the slope. Tracks of a running coyote following the deer were seen near the grove of trees, but beyond this shelter all tracks were blown away. A little beyond this point in a thick grove of trees, near which I had seen the band of deer from the creek bottom earlier in the afternoon, I came upon 11 deer, four of which were fawns and one a buck. The deer were standing in the shelter of the trees apparently avoiding the strong wind sweeping over the slope. As I approached a few steps nearer the hand, I saw four coyotes run off. One of them had been sitting by a clump of cedar about 20 yards from the deer and the other coyotes had been sitting a few yards lower down. The deer when first sighted seemed unconcerned, and when I approached they moved up the slope only a short distance. It seemed that the deer I had seen crossing the creek bottom had come from this band and had been chased a short distance by at least one of the coyotes. The observations suggest that the coyotes follow the bands of deer at times and thus have a chance to pick up weak animals. I do not know how readily the coyotes would attack a healthy fawn, but it would seem that they would not have a chance to do so if the fawn kept its head and refused to run away from the band. It is possible that through the evolutionary history of the deer, fawns that left the bands were eliminated, thus constantly reducing that tendency. Apparently coyotes are clever in detecting debility in an animal. As winter progresses and weak animals begin to appear, the coyotes seem to quickly form the habit of scrutinizing bands of deer for any such possibilities.

COYOTE PREDATION CORRELATED WITH RANGE CONDITIONS

The evidence is not conclusive, but observations on the general interrelationships between the range, deer, and the coyote suggest that there is a definite correlation between condition of the range and coyote predation on deer.

In the winter of 1936—37, when snow conditions were favorable to the deer, predation was light. The deer were in good condition and apparently were little molested by coyotes. In that winter some coyotes were weak, others died, appearing, at least superficially, to have starved in the midst of a heavy fawn population. Some predation apparently took place in the poorest part of the Yellowstone River range, but here also available data indicate that most of the fawns survived. The conditions existing in 1936—37 would indicate that deer in good condition were not subject to heavy coyote predation.

In contrast with the favorable conditions of the winter of 1936—37, those of 1937—38 were unusually severe due to crusted snow on the winter range along the Yellowstone River, combined with the scattered distribution of the food plants. Coyote kills appeared to be much more numerous in the winter of 1937—38 than in the previous winter, showing further correlation of predation with condition of range. Furthermore, during the winter of 1937—38, predation on the poorer ranges appeared to be much heavier than on the better areas. Six of the eight kills attributed to coyotes were found along the Yellowstone River and relatively more carcasses were found on this poor range than on the better ranges. However, it is not known what proportion of these carcasses were the result of coyote predation so that number of carcasses found is not necessarily an index of predation on a given range.

In the winter of 1937—38, when the fawns were in extremely poor condition, it seems likely that about the same number of fawns would have died on the ranges in the absence of coyote predation. The coyotes were probably preying upon fawns which, for the most part, were doomed to die from malnutrition or disease sooner or later during the winter. As pointed out elsewhere, several fawns were seen in an extremely weak condition, two of which were off by themselves, and others were known to have died from starvation or disease. The ease with which I ran down a weak fawn suggests coyotes have no difficulty in securing a fawn in such condition and that very likely bands are followed by coyotes in order to pick up such weaklings. If all the fawns in a band happen to be strong the coyotes probably seek food elsewhere. If deer in good condition were not able to ward off coyote attack, the relatively high survival of fawns often found in the midst of large population of coyotes would not exist, and the deer would long ago have been exterminated.

Coyote predation on deer increases as the winter season advances. The "big kill" is spoken of as coming in February and March. This might of course be due to snow conditions being adverse to the safety of the deer, but nevertheless the heavier predation coincides with the period of heavy mortality due to disease and malnutrition. The occurrence of greatest predation at a time when the animals are generally in a weakened condition also strongly suggests that the coyotes for the most part are getting the doomed fawns.

Figure 28— Winter range along the Yellowstone River below Crevice Creek
showing terrain likely to cause broken legs among deer.
March 21, 1938.

DEER-COYOTE BEHAVIOR

Behavior of adult deer when in proximity to coyotes shows that they are not afraid, but on the contrary are prone to assume the offensive. There was no indication that healthy adult deer were killed. Bucks generally pay little attention to coyotes, but does usually are more attentive and seem somewhat concerned, and their behavior suggests that they recognize the coyote as a potential enemy to their fawns.

Acting Supt. H. C. Benson in his annual report for 1909 states: "Quite a number of coyotes were killed last year—about 60 in all—but still they seem to increase. It is doubtful, however, if they kill much game, as the deer seem to be able to protect themselves. On several occasions last winter, I saw deer chasing coyotes instead of being chased by them."

Ranger Condon, who spent the winter of 1936—37 at Tower Falls, said that all winter the coyotes had great respect for the deer. When coyotes happened to come near, the hair on the deer's backs was raised, and the coyotes quickly moved off. The loose snow prevailing all winter was only a slight impediment to deer, but made travel difficult for coyotes. Consequently the former fared well, and had little regard for the coyotes as a source of danger. During the winter of 1938—39, Condon secured some exceptionally fine motion pictures of five or six does and fawns chasing a coyote.

Assistant Park Naturalist F. Oberhansley told me that he had seen a doe chase a coyote in January 1938 and that Ranger Elliot had also observed a similar incident.

On January 15, 1938, a coyote was observed passing within 40 yards of a group of does and fawns without disturbing them. The deer cocked their ears but at once resumed feeding.

On February 6, 1938, I observed three coyotes and six deer (including two fawns) feeding in close proximity at the Mammoth dump without taking much notice of one another. The deer fed at the choicest part of the dump.

Early in the morning of February 9, 1938, I caught a glimpse of a coyote passing through some willows along the Gardiner River, and, as I watched, caught glimpses of other coyotes traveling parallel to the first one a few yards to one side. Five coyotes were moving up the river in loose array, one or another stopping momentarily to sniff at something, and then moving forward with the rest. They probably had been feeding at an elk carcass. Upstream, ahead of the coyotes, a doe and fawn were feeding on a low rise above the river bottom. The doe caught sight of the coyotes coming up the river while they were still some distance away. After a few moments of sharp attention, she walked slowly and stiffly down the slope, with ears cocked and head held high. I did not see the coyotes as they came abreast of the doe, but as she came out on the bottom I saw her dash after one of the coyotes, chasing it in a small circle about a dozen yards across. The coyote, with its best efforts, barely managed to avoid the striking hoofs which were reaching out for it. After dodging away, it joined the others which had moved past. The doe returned slowly toward the fawn who had remained watching from the slope 40 yards away.

On February 18, 1938, on the slope of Mount Everts, a coyote was howling about 50 yards away from three bucks, who paid no attention. A doe with a fawn about 150 yards away cocked her ears in the direction of the coyote and took a dozen slow deliberate steps toward it. After watching it a moment she fled over a ridge out of sight.

On March 22, 1938, a band of deer, including some fawns, was feeding complacently about 100 yards from where two coyotes were sitting on their haunches.

Late in the afternoon of March 22, 1938, four coyotes were seen trotting past three does and two fawns feeding among some willows along the Gardiner River. The coyotes had been eating from two elk carcasses about 30 yards from where the deer were browsing. The deer took no notice of the coyotes; they probably had become accustomed to the latter feeding near them. On April 2, it was reported that several Civilian Conservation Corps enrollees had seen deer chasing coyotes in this area and it was thought by my informant that the deer were probably being attacked. However, since coyotes were feeding on an elk carcass in the area, it is more likely that the deer chased coyotes that were en route to the carrion.

On March 25, 1938, along the Gardiner River three does and a fawn, as they neared the crest of a hill, met four coyotes, who veered to one side to pass. The coyotes, after getting by, paused and sniffed about. The three does advanced toward them in a fanlike formation with slow and deliberate steps. As one of the does approached a coyote, the latter generally moved off to a safe distance, but two or three times a doe approached so near that by making a sudden dash it forced the coyote to scurry and dodge to escape. After a brief period the coyotes moved off. The fawn in the meantime stood watching from a spot behind the does. Later these coyotes slept on the snow about 150 yards from 11 does and 5 fawns, which were resting in the sun, many with closed eyes.

Figure 29— An old doe with teeth worn to the gums, some of them worn in two.
March 7, 1938.

Ranger John Jay told me that an acquaintance who worked for the hotel company saw three deer around a pile of rocks to which a coyote had retreated. Each time the coyote tried to leave the rock pile the deer chased it back. The deer and the coyote were still at the rock pile an hour later.

Observations indicate, then, that at times deer chase coyotes and at other times coyotes chase deer and prey on certain individuals when they are at a disadvantage. The coyote is by no means able to kill deer at will. An observation by E. J. Sawyer (Yellowstone Nature Notes, August 1924, p. 2) seems pertinent here :

A number of times during the past few weeks I have seen a weasel at grips and near grips with a Kennecott's ground squirrel. The circumstances vary in a rather puzzling way. Sometimes the weasel is in hot pursuit of the squirrel, the latter fleeing as if, indeed, for his life. Again, I have seen a large ground squirrel chasing a weasel and actually attacking him savagely; still again, a weasel and ground squirrel of average size in a catch-as-catch-can wrestling match, honors even, the participants finally going off in opposite directions, apparently none the worse for their encounter. A weasel living for weeks about the Buffalo Corral station seemed to be continually hunting ground squirrels when not himself pursued by them. The ground squirrels are especially abundant at this place. I have never seen either animal kill the other, though the ranger stationed there tells me he has seen the weasel kill the squirrels and take them into a hole. What is the explanation? Apparently the weasel preys on young ground squirrels, also on older ones when he can catch them off their guard, but he finds many an intended victim a match and even an over-match for him."

It would seem that carnivores will habitually attack only species with which they can cope successfully. But certain prey species are on the borderline, placing the carnivore and prey in a delicate balance of power that may easily be disturbed. Judging by the situation in Yellowstone the mule deer falls in this category. This species can readily cope with the coyote under normal circumstances and falls victim only when its power of defense is diminished by crippling injuries, old age, malnutrition, disease, or perhaps situations such as extreme snow conditions. There is latitude in the operation of ecological interactions, so that there may be exceptional cases.

STATUS OF DEER

Official counts of deer in Yellowstone made by the rangers show a steady increase since 1934. (Coyote control was terminated in the spring of 1935.) The counts by years are as follows: 1934, 363; 1935, 610; 1936, 673; 1937, 843; and 1938, 850.

Estimates made during these years vary from 850 in 1934 to 900 in 1938. The numbers of deer during these years probably has not varied greatly. However, there may have been some decline after the winter of 1934—35 when a number of deer died around the Game Ranch and near Gardiner outside the park. A heavy loss was probable that spring over most of the winter range. In reviewing the report on the 1938 census I note that the recorded population is a little low in a few localities, doubtless because of unfavorable counting conditions on the particular days when the census was taken. For instance, only 13 deer were counted in the Cottonwood area. About a week before the official count I found 90 deer on the area; and 10 days after the official count at a time when bare slopes had brought the deer out in the open to feed, I found 143. The official count along the Yellowstone River below Blacktail Deer Creek is also low. In these two areas the actual count, if made under more favorable conditions, would probably be 200 higher than the number recorded. The estimated population in this wooded area where counting is difficult would of course be a still higher figure. The actual count of deer in the park in 1938 should, therefore, be in excess of 1,000.

It seems probable that for some years the deer population has been held in check by range conditions and that the cause of mortality has been chiefly malnutrition and certain diseases, with other diseases and predation as secondary causes.

The primary winter deer foods now present in Yellowstone National Park are Douglas fir, sagebrush (Artemisia tridentata), yellowbrush, and to a lesser extent, in some localities, red cedar. Some food species such as poplar, service berry and willow, now scarce, probably once formed an important part of the diet. Other foods of less importance, because of their scarcity or lower palatability, are fringed sagebrush, greasewood (Atriplex oblanceolata), willow poplar, and Russian thistle. Over most of the range sagebrush is perhaps the most important winter food, at least on the basis of abundance and general use. Sagebrush was found in 24 of 39 stomachs examined during the winter. In 13 of these, sagebrush made up more than 50 percent of the contents, and in 3 more than 90 percent. Deer feed regularly on sagebrush, beginning in November (on the eighteenth 11 deer were seen feeding steadily on it) and continue well into the spring long after a variety of other green foods become available. Sage is heavily overbrowsed in places, especially on parts of the range near the Game Ranch and on the slopes of both sides of the Gardiner River. On some of these deer ranges, antelope have contributed to the overbrowsed condition of the sagebrush. Along the Yellowstone River the occurrence of sagebrush is spotted, and near Deckers Flat it is much overbrowsed. The best sagebrush range is on Reese Creek, the lower part of which has until recently been hunted so extensively that there has not been a heavy concentration of deer for more than a short time.

Douglas fir, an important deer food, now affords very little browse. Deer were often seen reaching high for the twigs, and even standing with the forefeet on rocks to better reach the browse. A fawn stomach contained 100 percent Douglas fir and numerous other stomachs contained lesser amounts, but many analyses showed no fir since it was not readily available to most of the deer. Deer and elk both are responsible for overbrowsing the fir, but since elk are present in greater numbers, overbrowsing is largely due to them. Scarcity of Douglas fir is one of the worst defects of the deer range.

Yellowbrush is generally distributed over the winter range and is much eaten by deer, but does not rank as high in the deer diet as sagebrush and Douglas fir. Red cedar (Juniperus scopulorum) is important along the Yellowstone River because of the local scarcity of Douglas fir browse. In the fall and spring, when the deer are still consuming winter forage, on the winter range, green grass is eaten in large amounts. From its first appearance in spring it is closely cropped, and makes up an important supplement to the regular winter food supply. Dry grass was eaten sparingly on a few occasions. It is very unpalatable to the population as a whole.

Figure 30— The old doe managed to rise and walk to the Gardiner River, where she fell and could not rise.
March 7, 1938.

To summarize, the data indicate that the status of the deer is dependent upon the condition of the range, particularly the condition of sagebrush, Douglas fir, and, to a considerably less degree, of red cedar and yellowbrush. The condition of the deer range is dependent upon the number of deer and elk. If there were fewer elk there would probably be more deer. It seems certain that for several years the deer have been pressing the range, the population being as large as the condition of the range and competition of the elk permits. Some years rather heavy mortality of deer has been reported while in other years the mortality has been light, depending, no doubt, on winter conditions and deer concentrations. Some fawns are killed by coyotes in winter, but it appears that this predation largely affects the weak animals, many of which would die before summer. Judging from the rather high number of fawns that come to the winter range, apparently few are lost during fawning time.