Region III Quarterly

Volume 1 - No. 2

October, 1939


By Russell K. Grater,
Junior Park Naturalist,
Boulder Dam National Recreational Area.

A short time ago I was talking with a group of visitors in one of our national park areas and the conversation drifted around to a favorite topic with most visitors -- the subject of wildlife. After a few minutes of discussion one man said, "Perhaps you, can answer a question that has been puzzling me for some time now. When I was in Yellowstone National Park I was told that the northern Yellowstone elk herd numbered a little over 9,600 animals in 1938. Now, what I would like to learn is how do they arrive at these figures for elk and how do they know that the figures are correct?"

That is a fair question and is similar to many asked by the park visitor regarding animals in all of our areas. The answer can be summed up in two words: wildlife census. Taking a census of the various wildlife forms found in any of our national park areas is a rather difficult matter. It calls for a carefully worked out plan in order to insure obtaining reaesonably accurate results.

In Yellowstone National Park the elk census is taken each year by what wildlife men call the visual method of enumeration. That simply means going into the field and making actual counts of the animals on the range. To do this requires the assistance of several men well trained in such work. The count is made, if possible, in late winter or early spring when the snow in the park is deep enough to concentrate the elk in more or less restricted localities. These areas are carefully checked as to location prior to the dates set for the count, and a crew of men is then assigned to systematically cover each area. Each day of the count the crew covers its allotted territory as quickly as possible, counting all elk observed. In addition, these crew members make notes on the condition of the elk and record the number of dead animals found. Any other large mammals encountered are also noted. All elk cannot be counted because small bands are certain to be isolated in outlying sectors of the park and will not be seen. After the count has been made and all reports are in, estimates are made regarding the percentage of animals actually observed. If it is agreed that 90 per cent has been recorded, then the total figure is obtained by adding an additional 10 per cent. Field notes taken during the survey will also show the relative number of other animals, such as predators, etc.

This same method of taking a census is also used at Grand Canyon National Park when the annual deer count is made on the North Rim each spring. However, in this particular area there is a fairly high percentage of uncounted animals, as large numbers drift into the canyons below the rim of the Kaibab Plateau and are not included. Thus there is a greater possibility of error in arriving at the final figure for the Kaibab deer herd as compared to the Yellowstone elk herd.

Visual counts are also used in taking the census of other wildlife forms such as bighorn, antelope, moose, waterfowl and the like. Most of these counts are made from the ground, but the airplane has become of great assistance in recent years, especially in the counting of antelope. Flying over a band of antelope it is an easy matter to take an aerial photograph of the entire group of animals and from this picture an accurate count can be made. Most waterfowl counts are made from a boat as it is necessary in many cases to flush the birds from cover, but on open water, counting through the aid of photographs has proven very successful.

The visual method of enumeration is the commonest and most reliable way of taking a wildlife census, but sometimes it becomes necessary to use other methods. This is especially true in the Southwestern park areas. In desert regions, such as Death Valley and Organ Pipe Cactus National Monuments and the Boulder Dam National Recreational Area, weather conditions are much too mild during the winter months to force animals to concentrate in any one area, and it is only during the heat of the summer that any pronounced tendency for wildlife concentrations is noticed. During these hot months, every available waterhole is usually an excellent place at which to start a census of the larger wildlife forms. Bighorn can be observed at these waterholes with great regularity. That is also true of wild burro, coyote, fox and other species. In such areas it is necessary to use an indirect method of enumeration to supplement the visual in making counts.

This method consists, in the main, of carefully examining the area selected for such things as tracks, droppings, evidence of browsing, and dens. A thorough knowledge of the terrain is absolutely necessary and the habits of the animal being studied must be known.

In taking a census of such animals as beaver, the use of indices furnish the only reliable source of information. Inasmuch as beaver are primarily nocturnal it becomes necessary to place great reliance upon such things as tracks, abundance of food, cuttings and dens. Studies by reliable field research men have already indicated the number of beaver known to occupy an average den. Thus, by obtaining a fairly accurate figure on the number of occupied dens in a given region and supplementing these data with other observations, such as food storage piles, etc., it is possible to arrive at reasonably accurate census figures.

The indirect method is also of great value in the Boulder Dam National Recreational Area where the creation of Lake Mead has produced an unusual problem in census taking. Instead of a few places heretofore containing water available for wildlife, the huge lake now offers a 550-mile shoreline as a water source. Thus, during neither hot nor cool months is there any tendency for animals to concentrate in any one area because of water needs.


Let us suppose that we are going to attempt to obtain figures on the bighorn population in Boulder Canyon up the lake from Boulder Dam. Preliminary field surveys may not disclose any bighorn, but a careful examination will show the presence of droppings and tracks in a few of the side canyons -- evidence of the presence of the animals as surely as though the observer had actually seen them. The location of these "signs" is then put on a map of the Boulder Canyon region. As these field surveys are continued, the map will soon show the localities known to contain bighorn and the frequency of occurrences as indicated by the abundance of tracks and droppings. Armed with this knowledge, the census taker now selects one of the side canyons believed to be representative of the number known to contain bighorn. Here the direct visual method of enumeration is utilized, the canyon being searched from top to bottom throughout its length. Powerful binoculars are an absolute necessity, as the bighern usually knows of the presence of the census taker long before he himself is seen and can frequently slip away unseen unless field glasses are brought into play. The binoculars also aid the searcher to closely examine overhanging ledges on the canyon slopes. Bighorn are especially partial to these ledges because of the shelter from the sun rays and often lie there well out of sight of the casual observer for hours at a time.

After making an intensive survey of the canyon, the census taker finds that he has seen five sheep in the entire area. With this minimum figure as a gauge, he can safely say that the other canyons in the region of comparable size, food, and bighorn sign will contain a similar minimum number. In this manner a total is obtained for the Boulder Canyon area that will tend to be conservative and to portray conditions much more accurately than mere estimates based only on a few miscellaneous observations. While this way of taking a census has a greater possibility of error than the direct visual method which covers an entire region, it is the safest means of obtaining anything resembling accurate figures for the Lake Mead area. It has been carefully followed in working out the census figures for the western end of the Grand Canyon. Here it would be almost impossible to use any other method due to the relative inaccessibility of many of the huge side canyons. Similar methods are utilized in enumerating the wild burro population of the region.

Speaking of wild burros, a rather interesting discovery was made while checking a sample canyon. A careful survey had revealed only seven animals for the entire area, yet "sign" was abundant and everything seemed to indicate that more should be present. For some time I sat there on a rock trying my best to locate other burros in the neighborhood, but without success. Look as carefully as I would, not another animal was in sight. Finally, acting on an impulse, I drew out a small caliber automatic and discharged it twice into the air. The results were really astonishing. From all parts of the canyon came alarmed brays as the slopes literally became alive with burros. A quick count showed a total of eighteen instead of the original seven -- and I may have missed one or two even then. Watching me from behind rocky outcrops, the animals had blended perfectly with the dark colors of the canyon and did not become distinctly visible until frightened into emerging from their hiding places.

The values of taking a wildlife census are many. Naturally it gives a fairly accurate picture of the general distribution and abundance of any given species in the park area. Probably the greatest benefit derived from such a census is obtained in planning a carefully coordinated wildlife program for the park. For example, on the North Rim of the Grand Canyon the National Park Service and the U. S. Forest Service are carrying on range studies to better determine the relationships that exist between the Kaibab deer herd and the plants in the park area and on the remainder of the plateau. To carry on such studies, grazing quadrates are established at various points on the plateau. These quadrates are small plots, fenced against deer and containing representative vegetational growth for the locality. Adjacent to the fenced area is another plot, identical in size but unfenced and containing similar vegetation to that of the protected plot. Each year the browse plants in these two tracts are carefully measured and charted on graph paper and the abundance and growth of other plants having any food value are noted. The figures obtained each year will show the normal growth of the protected plant as compared to the growth of a similar unprotected plant subject to deer browsing. With these figures it is then possible to determine whether the range is being over-browsed, under-browsed or about right. If over-browsed, it becomes necessary to work out plans to reduce the number of deer in the region, and here the importance of census figures becomes quite evident. Knowing how many deer are in a given region, it is a relatively simple matter to determine the approximate number of animals that must be removed from the range in order to insure healthy conditions for the following growth season. The next year's figures from the quadrates should show whether the preceding season's program and calculations have obtained the desired results.

Taking the annual wildlife census is one of the most interesting tasks carried on in the park areas, but one that requires skill, patience and physical endurance as well as wildlife knowledge. But whether the census taker is fighting his way on skis or snowshoes through the deep snows of Yellowstone, spending days in the saddle scouring the forests and exposed flats of thee Kaibab Plateau, or laboriously carrying canteen and equipment into the desert canyons of the Southwest, he can be sure of one thing: He does not know what the next day will disclose, but he does know that he will not experience many dull moments.

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Date: 17-Nov-2005