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Fauna Series No. 4






Population and Mortality







Other Larger Mammals

Small Mammals


Misc. Diet



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

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