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

STUDY TECHNIQUE

IN STUDYING the role the coyote plays in the Yellowstone faunal complex I tried first to learn the food habits of the animal. But his food habits do not tell the whole story, for after we learn what the coyote eats it must be determined what effect it has on the prey species.

The food habits were studied largely by means of dropping examinations. Droppings were gathered at every opportunity from all localities visited, special efforts being made in critical areas to get numbers large enough to be significant. Localities selected for special study included water bird nesting and wintering habitats, and elk, bighorn, and antelope fawning grounds. Rather large collections of droppings were secured from the following areas: Old Faithful, Gibbon Meadows and Elk Park, Virginia Meadows, Swan Lake, Tower Falls, Specimen Ridge, the Horseshoe, Buffalo Ranch, Hayden Valley, Pelican Creek, and a stretch along Willow Park. Smaller collections were secured from other localities. The quantitative data on food habits secured from the examination of droppings were supplemented by observations of the animals in the field.

In winter, information concerning the food habits of coyotes on the winter game ranges could best be secured from general field observations, for it so happened that the coyotes were living largely on elk and deer, mainly in the form of carrion. At this season it was more difficult to secure a large collection of droppings, for frequent snows and trampling prevented an accumulation of them on the surface of the trails. Enough winter droppings were examined, however, to substantiate the field observations.

In studying food habits by means of droppings it is essential that they be properly identified. Since coyote droppings vary considerably in size and conformation according to the quantity and kind of food eaten, there would be considerable question as to proper identification in localities where other predators are also present in large numbers. In Yellowstone where foxes, lynx, and wolves are very scarce, or absent, and badgers relatively scarce, there was little chance of many misidentifications.

Some droppings were examined in the field or at camp. Where difficulty was encountered in making identification in the field, the contents were wrapped in paper or cheesecloth and examined with care later. Most of the material was examined at Jackson, Wyo., where comparative specimens for identification were available. At Jackson each dropping was washed in a sieve or in its cheesecloth wrapper before being examined.

In analysis, the number of droppings in which an item occurred and the number of individuals present were tabulated. Volume was not measured. To determine the number of individuals of a species present in a dropping the part of the anatomy was used which gave the highest count. For instance if two left mandibles, three right mandibles, and two right femurs of a pocket gopher were sorted out, the right mandibles would show that at least three pocket gophers were represented in the droppings. The bones of the skull, particularly the rostrum and the mandibles, the long bones, and sometimes the tails were most useful as an index of the number of individuals represented in a dropping. Although sometimes the quantity of fur present indicated that more than one animal was represented, if such could not definitely be proven only one individual was tabulated. By following this conservative policy some individuals of the smaller mammals were no doubt missed, but the number missed is probably not significant and is at least partially compensated by possible duplications elsewhere.

The different species of field mice and of some of the other genera represented by closely related species were lumped since, for the purposes of this study, it was felt that it was not worth the considerable effort involved in making specific identifications.

Special effort was made in the field to get information on the amount of carrion taken since it is highly important to know the cause of death of animals utilized. This information is very difficult to obtain, but in some cases sufficient data were secured to greatly change the conclusions which one would ordinarily reach. Considerable data were secured on the condition and age of animals that were killed by coyotes and of those available as carrion.

It is more difficult to determine the effect of the coyote on prey species than to learn the food habits of the animal. In cases where the food-habits study shows that a species is eaten to only a limited extent it usually can be concluded that the effect of the coyote on the species is negligible. If the status of the prey species is favorable it can be concluded that any coyote depredation taking place is not harmful to the species. Conversely, when the status of a prey species is unsatisfactory it becomes important to determine the part the coyote is playing. In some circumstances all factors bearing on the species must be studied.

Considerable space in the report has been given to the food habits and inter-relationships of the ungulates. Emphasis has been given to this phase of the study because much big game predation in the light of data at hand is closely bound up with condition of the animals, which in turn is dependent upon range conditions. Effort was made to investigate the survival of the young at various times of the year and to correlate winter survival with forage supply. Sample counts of the ungulates were made to learn the percentage of young present in the population at various times of the year. In effect, the problem demanded considerable information on each species and much attention was given to this phase of the subject.

ITEMS IN THE COYOTE DIET

DURING the course of the study 5,086 coyote droppings, containing 8,969 food items, were collected. With the exception of less than 200 of them, containing 185 items, all droppings were gathered from the first of April to about the middle of November. Of the 185 items present in those collected in winter, 119 were deer and elk remains and more than 50 of the remainder were in droppings which had undoubtedly been deposited in the summer and fall. The following table, therefore, except for about 119 items of deer and elk, pictures the food habits during the April-November period.

In addition to the foregoing, more than 200 winter droppings not included in the table on page 43, were examined in the northern part of the park. These contained deer and elk remains. In this area where deer and elk winter, these animals, mainly as carrion, make up practically the entire food supply. In the interior of the park snowshoe hares and mice enter more extensively into the winter diet.

About 3,500 droppings were obtained during 1937, a few in 1936, and the remainder in 1938. The material was not tabulated separately for each year since there was no significant difference in the incidence of the items.

Below are listed the number of individuals of each item found in the droppings. Except in the case of the field mouse and pocket gopher, and in a few instances the ground squirrel and deer mouse, the number of individuals present coincides with the number of droppings in which they occurred. Such items as insects, vegetation, and carrion were arbitrarily listed as number of times occurring, rather than number of individuals, since such material is not otherwise readily comparable with the other food items. For instance, the number of individual grasshoppers, crickets, june beetles, snails, pine nuts, rose seeds, mushrooms, blueberries, and Oregon grape is not given. However, in the discussion of each item the quantity present is usually indicated. The percentages given in the table are based on number of individuals, treating times of occurrence of these few items as individuals. The seats are not always accurately dated. Some collected in spring especially along streams, may be winter droppings. However, the dates of most of them are sufficiently accurate to furnish a picture of coyote diet on a seasonal basis.

Classification of 8,969 individual food items found in 5,086 coyote droppings gathered in Yellowstone National Park