Fauna Series No. 4

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

CHAPTER X:
SMALL MAMMALS IN RELATION TO COYOTES

Figure 46— Tracks show how coyote followed along a snow bank, bordering a road opened up by the snow plow,
hunting mice which come out in the road from under the snow.
Swan Lake Flat, April 14, 1938.

FIELD MOUSE

THE FIELD MOUSE, Microtus sp., along with pocket gopher, is the staple food item in the coyote diet from April to November. During the winter months some field mice are eaten but they represent a minor item in the diet over most of the winter range, where other foods are more available. This was especially true in the winter of 1937—38 when the snow was crusted and there was much carrion. When snow conditions are favorable and mice abundant, the coyote can subsist quite well on mice even though a foot or more of snow covers the ground. A total of 3,044 or 33.9 percent of the 8,969 food items were field mice. They occurred in 2,155 droppings.

Accurate measurements of field mouse population could not be made, but from general observations it was apparent that the populations were high in the spring of 1937 when the study was begun, and remained high during the winter of 1937—38. There seemed to be, from general observations, some slight reduction in the population by the beginning of 1938. In Jackson Hole, immediately south of the park, great numbers of field mice were found dead during the winter, and they became relatively scarce by the summer of 1938.

During the spring, summer, and fall, coyotes spend much time in the meadows hunting mice and pocket gophers. This occupation seems to be successful on the last spring snow, for coyotes often hunted there when bare areas were available. To illustrate the mousing behavior a few descriptions from my notes are given.

On May 14, 1938, at Willow Park I watched from 9:45 a. m. until 11:30 a. m. two coyotes hunting over a broad expanse of snow which was more than a foot deep in places. Much of Willow Park was bare of snow but these coyotes confined their hunting to the snow field. A single coyote was hunting mice near me when I started watching, but in a few minutes a second coyote came out on the snow from the woods opposite. By 10 o'clock the near coyote which I had been watching had moved to the far side and the other had come quite near where I was hiding. Between 10 and 11:30 o'clock the latter was seen to capture and swallow 11 animals, all of which appeared to be field mice. For about 10 minutes of the period the coyote was out of my view so it may have captured one or two others, and undoubtedly captured one or more mice during the 15 minutes it hunted, when I was watching the other coyote. In places the snow seemed to be crusted, for in pouncing, the coyotes occasionally were not able to break through the surface. Usually the mouse was not captured on the first pounce, but only after further quick strikes with the paws, three or four of which were sometimes made after the original major pounce. Sometimes the coyote would dig and paw for a minute or two before catching the mouse. The closer the coyote approaches to the point of capture, the more agitated it becomes, as is indicated by vigorous tail-wagging. Several times increased excitement on the part of the coyote was followed immediately by the capture. Once or twice a coyote was seen to cover 10 or 15 yards in four or five jumps before pouncing. Once, one of them ran about 15 yards and picked up a field mouse which was on the surface. In one place a second mouse was caught by further digging in the snow. The first pounce probably destroys the runways thus closing off ready avenues of escape and allows the coyote to pounce more accurately a second or third time. The coyote catching the 11 mice pounced without success about 30 times. These misses were in the snow, but in grassy areas misses were also frequent. The coyote was a male and seemed to be an adult. Once one of the coyotes stood at attention ready to spring for 5 minutes and then walked off without following through. Seven of the mice were caught in an area not more than 100 yards across. Both coyotes hunted throughout the period that I watched and were lost to view when they moved into the woods. At 4 o'clock a coyote was again hunting on the snow in the same locality.

Figure 47— Typical attitudes of a coyote catching a mouse.
Sketch from life by O. J. Murie.

As a coyote approaches a spot stealthily, it places each foot on the ground slowly and only gradually letting down its full weight. Sometimes it watches and listens with one forefoot poised in the air. Frequently a mouse is scented or heard while the coyote is trotting. It will then come to a stop, walk stealthily a few steps and poise for the spring. Standing with all four feet held slightly together, nose pointed at the spot, and ears cocked sharply, its body sways back a perceptible amount. Many times before actually leaping the coyote assumes a tense position only to relax and wait for the right moment. Generally the coyote springs high in the air and drops on its prey, hitting it with the front feet. The forelegs are held straight and braced to take the jar as it strikes. When the victim is caught beneath a mat of grass, the coyote must carefully paw aside the grass to get its prey.

Ranger Lee Coleman told me that in Pelican Meadows where the snow lies deep in winter he has frequently found coyotes hunting mice over areas which the buffalo have partly cleared in feeding. In these meadows where there are sometimes more than 200 buffalo wintering, this symbiotic relationship may be quite important at times to the few coyotes staying there.

On Swan Lake Flat on April 14, 1938, coyotes had been traveling the sides of the road along the snow bank made by the rotary plow. The fresh snow showed that many mice had come out of the base of the drifts onto the road. I saw a deer mouse which for several yards was unable to find a retreat in the snow. The coyotes had quickly learned of this mousing opportunity and had been there hunting.

Figure 48— Sagebrush killed by mouse birdling: part of a patch of 600 square yards
in which it was estimated one-fourth of the sage had been killed.
Across Lamar River from Buffalo Ranch, June 7, 1938.

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