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

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.

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