Date of this Version
The best known vertebrate pests, as the papers presented at this meeting show, are birds and mammals. Other vertebrates, however, may become pests also: sharks, lampreys, toads (they fall into swimming pools), geckos, tortoises and snakes, for example. Without considering them, however, the depredations by birds and mammals alone are so varied that no single method of pest control can ever be all-embracing. Certainly, no one would suggest that acoustical methods would be, but, with further study, acoustical pest control should be much more widely used. I hope to point out here the possibilities and a few realities in bio-acoustics as related to control of vertebrate pests. First, let us consider an aspect of acoustical pest control that seems to attract attention: the possible use of ultrasonics. Ultrasonic sounds, defined with man as reference, have frequencies above those heard by man; otherwise they are the same as other sounds. Since biologists who study the effects of liquid-borne ultrasounds on living things usually use very high intensities, causing injury by their high energies, many people believe that ultrasonic sounds have an aura of mystery. This is not so. Ultra-sounds have few special properties. Obviously, if ultrasonic sounds could be used for pest control, human beings would not hear them, and this would be advan¬tageous. However, the pests usually must hear the sounds, and this means that they must have higher ultrasonic limits than that of man. Rats, mice, and other small mammals can hear sounds that are ultrasonic for man, so acoustical stimuli for them could be inaudible to man. Birds, however, generally have ultrasonic limits lower than that of man, and for them audible sounds must be in man's sonic range. Periodically, stories appear in newspapers about the chasing of birds, usually pigeons, with ultrasonic sound. When any reasonable information is given, one usually finds that this was done with a sound source that produced ultrasonic sound well enough, but produced high intensity sonic sound as well. Invariably no effort was made to distin¬guish between the effects of different frequencies. In short, ultrasonic sounds may have advantages in pest control, but they are not likely to be somehow "mysteriously" effective. Ordinary loud noises have been used since antiquity to repel birds and mammals. These can be produced variously, from clapping hands to firing cannons. Many people believe, when they shoot at animals, that the animals flee because they fear death. It seems highly doubtful, from what we know of the conceptual abilities of birds and most mammals, that they can fear an abstraction such as death. The animals are undoubtedly frightened by the noise. Since this is the case, one is inclined to wonder why it has taken so long for firecrackers and guns to be discarded in favor of safer and cheaper mechanical noise generators or recorded shots. The latter, particularly, should be the item of choice for chasing birds, where high intensity noises can be used. Why should anyone use blanks, firecrackers, or exploders, which are expensive at best, when they can simply clap their hands in front of a microphone and produce a recorded "shot" which is infinitely reproducible?