Fauna of the National Parks
of the United States
PROBLEMS OF COMPETITIVE ORIGIN
Though the whole of a national park is nominally a primitive area, in reality the condition of its wild life varies from almost complete wildness in remote sections to high artificiality in the centers of human population. The violent disturbances of the normal biotic relationships around these development areas engender many acute faunal problems. As these are man-made situations, human intervention to correct them is not a transgression of policy. But just as in every other wild-life problem in a park, no action is permissible until a proper investigation has revealed that the condition is absolutely referable to an artificial cause and that the proposed remedy is not in itself likely to have injurious effects.
As has been suggested, the injury to landscaping around buildings may be due not so much to the utilization of forage by normal animal numbers as to the depredations of abnormally congested animal populations. This abnormal congestion may be caused by the absence of the control species. The control species, in turn, may have been displaced by the development of the area. Thus, the whole vicious circle completes itself. In each park the complex faunal maladjustments which exist in the vicinity of hotels, camps, and utility areas should be carefully studied and definite stabilizing programs formulated upon the findings. It is not sufficient to say that natural conditions are impossible in these sections and to let it go at that. Though they can never be truly natural, they can be improved and made to be more nearly natural. It is the more important in that these are the very places where it is desirable, from the visitor's standpoint, that the true story of wild life should be told. More people see animal life around the camps than anywhere else, and the majority of ranger-naturalist trips are made in their immediate vicinities.
The floor of Yosemite Valley. No other spot in a national park has as many wild-life problems of this type. Permanent residents alone number several hundred, and there are days when ten to twenty thousand people and thousands of cars are circulating in an area approximately 6 miles long by 1 mile wide between the great confining walls. They constrict the seasonal drift of game into a bottle neck. These walls tend to isolate the characteristic transition-zone fauna of the valley from any near-by source of replenishment. Further, the cliffs restrict the movements of visitors, with the result that by far the greater percentage of them never leave the valley itself. Wild life of the floor is the only wild life that they see in the park. Hence, it is of the utmost importance that this part of the park fauna be preserved intact.
Yet it is only because the natural conditions are so abundantly favorable that the wild life has resisted decimation as well as it has. Probably every plant and animal has been affected by human invasion. Some of the more conspicuous adverse influences are discussed here. No criticism of the splendid administration of the area is implied, the purpose being merely to demonstrate some of the adverse effects of human populations upon the faunal resources.
(a) Oil is spread on dead waters seasonally as a mosquito-abatement measure. This spells death to birds of many species that come to the quiet pools to bathe. One of the writers has picked up dozens of oil-soaked birds in the meadows, and within the space of a half hour once saw two blackbirds and a robin floating down the Merced River. Total losses from this source must be considerable.
(b) Clean-up work. Many standing snags have to be removed in the interest of human safety because they are located near roads and buildings. This has unfortunate consequences in the elimination of necessary nesting, concealment, and food habitats for many species of both birds and mammals, including flying squirrel, screech owl, spotted owl, saw-whet owl, pigmy owl, hairy woodpecker, willow woodpecker, white-headed woodpecker, pileated woodpecker, California woodpecker, red-shafted flicker, violet-green swallow, red-breasted nuthatch, and mountain chickadee. Fortunately, the policy of allowing dead trees to stand wherever possible has been in force in the valley for some time.
Dead brush and downed timber must be largely removed where there are so many people, and the visitors utilize all dead wood available around their camps for kindling. This means a habitat loss for a long list of mammals and birds.
(c) Trampling. Barriers are skillfully used to keep automobiles to the roads and parking areas. Paths are provided both for pedestrians and for horses. Nevertheless, the destruction of ground plants by millions of trampling steps is tremendously effective in destroying the food and protective cover of such vertebrates as deer, chipmunks, and ground and bush-nesting birds. Yosemite has set the example in adoption of measures to minimize the sheer physical destruction to wild life resulting from concentrated human populations.
(d) People accidentally reveal concealment places of nests and of young to lurking enemies. In Yosemite countless bird nests are discovered by humans who do not harm the eggs or young themselves but all unwittingly betray them to marauding blue-fronted jays and squirrels. This tends to increase the losses from these sources abnormally. Moreover, the jays are, if anything, more abundant than normal because man has brought them an increased food supply. In this particular instance the effect of development is to help the enemy and injure its prey.
Fawns of mule deer are secreted in the tall clumps of saw grass and in other nooks about the valley during the first days of their lives. Their spotted coats make them inconspicuous, and the members of this family have an added protection in being scentless when they are very small. When visitors go to the hiding places or handle the young fawns, they leave a blazed trail for the predators to follow. Black bears and coyotes frequently kill fawns in the meadows and this may be one reason why they discover them more easily.
(e) Relation of travel season to food supply. During the summer season the food supply of some animals is greatly augmented and their numbers about development centers are increased thereby. In Yosemite Valley this is certainly the case with black bears and, very probably, with mule deer. When fall comes this artificial food is no longer available and the drain on the natural food becomes very heavy, with detrimental results to both forage and animals.
(f) Displacement of predators in its effect upon rodents and ungulates. Where man's presence influences one species adversely, the fact that it also keeps enemies of that species away is a compensating factor. But for species that thrive near civilization, the absence of the controlling predators increases the problem.
Mountain lions shun the valley. Even if their numbers were normal for the park as a whole, they would not linger where there are so many people. Both wild cats and coyotes frequent the valley, but do not hunt too near the camps and buildings. The same is generally true of the larger hawks. Consequently man has not only favored the California ground squirrels with an excellent food supply, but he has protected them against their natural enemies until they have multiplied greatly. This is one instance where safe control measures applied to those particular areas would be actually beneficial to wild-life values. Shooting the squirrels around buildings or camps is perfectly safe and sufficiently effective as a control measure.