Fauna Series No. 4

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

CHAPTER VII:
ANTELOPE IN RELATION TO COYOTES

RELATIONSHIPS OF BUCKS TO DOES AND FAWNS

During the summer it is usual to find a buck with each band of does and fawns. The buck at this season may do considerable herding of the company. Many of the bucks are alone, or in groups of two to a dozen or more. About the middle of September the rut begins and a buck with a band of does and fawns chases away all other males. If not successful in this he hangs on the outskirts of a band, or possibly wanders from one band to another. Quite often during the summer bucks have been seen chasing single does. Sometimes the run is long enough to cause both animals to pant, with mouths open. To escape the buck the doe sometimes resorts to considerable dodging. Several times in late May a buck was observed chasing a heavy doe for a distance of about 500 yards. In winter the bucks and does intermingle in various proportions, and at that time the bands are frequently breaking up and re-forming. The presence of a buck with a herd of does might insure some added protection to the fawns from coyotes.

Figure 34— Most of the sagebrush in the picture has been killed by overbrowsing.
Antelope had fed in the area on the scanty food still to be found.
Game Ranch Area, January 13, 1938.

FAWN SURVIVAL

Season of 1937.—During the summer it is not always easy to get antelope counts showing true proportion of fawns, for at that time some of the fawns or some of the does may be segregated by themselves, or several of the fawns may be following one or two does. On June 28, 1937, for example, seven fawns were following one doe. Another doe was followed by three fawns, two of them the same size, one definitely larger. At Yanceys, after making repeated counts, it was felt that a fairly good summer census of the does and fawns was obtained. Some of the more complete counts made at Yanceys are here tabulated. It will be noted that the early summer ratio was maintained throughout the summer. Yearling does are included under "doe" as it is hard to differentiate them.

Reliable counts made over same area at Yanceys

Other summer counts were made but since they were not as comprehensive they may not represent true ratios existing in the areas:

¹Apparently many yearlings.

The following tabulation shows results of two fall counts of the herd, each made over a 3-day period. There was only a slight possibility of counting any animals twice in either count.

First Count

Second Count

The ratios of adults to fawns in the two counts are 29 percent and 27 percent, respectively. It will be noted that a smaller proportion of bucks are tabulated in the first count than in the second. However, most of the 54 animals classified as "adults" were bucks (I did not have time to precisely differentiate the does and bucks before they ran off) so the doe-buck ratio was actually not very different in the two counts. The first sample represents more than half the antelope herd so the fawn ratio attained is fairly representative of the true ratio, especially since other ratios obtained in various counts during the winter lie so near this.

At various times between January 12 and May 3, 1938, animals on the winter range were classified when opportunity offered. Of 1,494 animals classified, with of course many duplications, 331 were fawns. This gives a 28 percent increase of fawns, a ratio midway between the percentages of 27 and 29 secured in the two large counts made in November. The sex of adults was identified only in a group of 443 animals, 173 being bucks with the same number of does, and 97 fawns. The percentage increase in this sample is also 28 percent.

The fawn survival during the winter was high. The ratio recorded for March, April, and May was about 4 percent higher than that for January and February. This fawn increase probably is not of statistical significance, but points to a high winter survival of young.

Season of 1938.—On July 14, 1938, I counted at Tower Falls 1 buck, 28 does, and 12 fawns. This was an incomplete census of bucks, and may also have been incomplete for does and fawns.

On August 30, I was told by some of the local people that fawns were very scarce in the Gardiner area and that it was thought the coyotes were "getting all the fawns." I made a count between Gardiner and the Game Ranch with the following results: bucks, 13; does, 38; and fawns, 27. The fawn ratio, rather than being low, was unusually high in this particular area.

The total of various counts made between July 14 and October 1 in the Gardiner, Blacktail, Yancey, Horseshoe, and Buffalo Ranch areas is as follows: bucks, 23; does, 126; and fawns, 63. If we consider the sexes of adults equal in number, which they appear to be, and assume the number of adults to be twice the doe count, the increase is about 25 percent.

Practically all of the antelope had moved down to the winter range by November 11, 1938, having come down a few days earlier than in the preceding year, probably because of the earlier arrival of cold weather and snow. Two hundred or more had moved outside the park below Reese Creek by the middle of November. One band was reported near Livingston, more than 50 miles from the park. These were seen some distance from any area where antelope were known to regularly occur. It was presumed by some people that they had wandered down from Yellowstone National Park, but the real source of these antelope was not known.

On November 12 I counted and classified 351 antelope. Of these, 202 were feeding in an alfalfa field. The fawns were no doubt especially fond of frozen alfalfa for the ratio of fawns to adults was much higher than among the antelope outside the field. On November 15 a second count was made. At this time there was still a concentration of fawns in the alfalfa field.

November 12 Count

November 15 Count

The sample count made on November 12 shows an increase in the herd due to fawns, of 30 percent. Since there was a concentration of fawns on the alfalfa field, it is difficult to know whether a true ratio was secured. However, it is possible that enough animals were counted away from the field to compensate for this concentration. The buck count is considerably lower than the doe count so perhaps the adults were not fully represented. If the percentage of increase due to fawns is based upon the assumption that the adult herd contains as many bucks as does, or a total of 310, then the increase is 26 percent.

The second count, made on November 15, is probably less representative than the first one, for there was still a concentration of fawns in the alfalfa field and a smaller number of animals were counted. The relatively high count of fawns away from the alfalfa field was due to finding one band containing a high fawn ratio which apparently had just left this field.

On February 27, 1939, 44 antelope were counted on Rattlesnake Butte, and on March 1, 519 were counted near the Game Ranch and outside the park below Reese Creek. In the latter case 495 were outside the park. There probably was no duplication in these two instances so they are tabulated together.

February 27 and March 1, 1939, Counts

As the count includes well over half the total number of antelope in Yellowstone Park it should represent a good statistical sample of the population. The increase in the herd due to fawns is 24.8 percent, this being a little less than the percentage increase in November counts and a little less than the percentage increase found in the 1937 fawns.

The survival of the 1937 and 1938 fawns appears to be sufficient to bring about an increase in the antelope population since losses of adults were apparently light.

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