NERC 88/29
AFESC TR 88.14
JUNE 1988
Engineering and Services Center
U.S. Air Force
Fish and Wildlife Service
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AFESC TR 88-14
NERC-88/29
June 1988
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Suggested citation:
Manci, K.M., D.N. Gladwin, R. Villella, and M.G. Cavendish. 1988. Effects of aircraft noise and sonic booms on domestic animals and wildlife: a literature synthesis. U.S. Fish and Wildl. Serv. National Ecology Research Center, Ft. Collins, CO. NERC-88/29. 88 pp.
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This report was produced as the result of a cooperative research project between the National Ecology Research Center, Ft. Collins, Colorado and the Air Force Engineering and Services Center, Tyndall Air Force Base, Florida, on the effects of aircraft noise and sonic booms on animals. The effort was funded by the Air Force's Noise and Sonic Boom Impact Technology Program, Wright-Patterson Air Force Base, Ohio.
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EFFECTS OF NOISE AND SONIC BOOMS ON DOMESTIC ANIMALS AND WILDLIFE |
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The U.S. Air Force must be able to conduct flight operations in assigned airspace over public and private lands to train personnel and test new technologies to fulfill its national defense mission. The Air Force can only fulfill its mission by maximizing use of current aircraft operating areas and varying military training routes to give pilots added experience. Acquiring and maintaining new airspace is vital in light of increasing mission requirements and international agreements. These actions will impose aircraft noise on the environment which may affect wildlife; thus, these actions fall under the auspices of the National Environmental Policy Act (NEPA) of 1969. NEPA requires all Federal government agencies to analyze the environmental impact of proposed Federal actions "significantly affecting the quality of the human environment" (42 USC 4341).
A great deal of research was conducted during the 1960's and 1970's to determine the likely effect of commercial supersonic jet aircraft on the environment, focusing on the effects on humans, due to public fear of adverse ecological impacts. However, the knowledge gained from this research does not apply directly to wildlife on areas overflown by aircraft at supersonic speeds and at low altitudes.
Although scientists have researched some effects of noise on animals, many data gaps still exist on the overall effects of aircraft noise on wildlife. In addition, perceived inadequate or inaccurate analysis of the effects of aircraft noise on wildlife by the general public has resulted in delays of flight operation expansions.
An information base on the effects of aircraft noise and sonic booms on various animal species is necessary to assess potential impacts to wildlife populations from proposed military flight operations. Thus, in a joint U.S. Air Force/U.S. Fish and Wildlife Service effort, the National Ecology Research Center conducted a literature search of information pertaining to animal hearing and the effects of aircraft noise and sonic booms on domestic animals and wildlife. Information concerning other types of noise was also gathered to supplement the lack of knowledge on the effects of aircraft noise. The literature is summarized in this report to provide an overview of current knowledge. No attempt was made to evaluate the appropriateness or adequacy or the scientific approach of each study. A brief overview of the physics of sound and aircraft noise and sonic boom characteristics also is included to familiarize the reader with the terminology and concepts of aircraft noise and sonic boom impact analysis.
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Sound is a pressure fluctuation in the otherwise undisturbed atmosphere or other medium (e.g., ground or water). Although these fluctuations may be relatively small in magnitude, large pressure differences exist between the faintest audible sounds (e.g., leaves rustling in the wind) and the loudest audible sounds (e.g., a rocket launch or bomb explosion). This difference in magnitude is measured in terms of the amplitude of the pressure fluctuation.
Acoustical research has shown that the ear responds to sound pressure level in a logarithmic manner (Hurturbise et al. 1978). Consequently, sound pressure levels are measured with the logarithmic decibel (dB), which corresponds reasonably well to the biological properties of the human ear that determine loudness perception. The zero-end of the scale approximates the lowest level sound that an average human can hear [about 20 micro-Newtons per square meter (mN/m2)]. A value of about 120 on the scale corresponds roughly to the point at which sound becomes painful (Table 1).
Table 1. Comparison of sound pressures and sound levels from typical sources (Ewbank 1977).
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2,000 |
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Peak leavel at ear of 0.303 caliber rifle |
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200 |
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Jet aircraft taking off at 25 m |
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20 |
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Human pain threshold |
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2 |
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Very noisy factory |
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0.2 |
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Ringing alarm clock at 1m |
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0.02 |
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Ordinary conversation at 1m |
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0.002 |
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Quiet office |
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0.0002 |
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0.00002 |
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Threshold of human hearing |
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Due to the sound pressure compression of the decibel scale, the combined noise produced by two identical jets is, in general, only about 3 dB higher than that produced by either aircraft operating alone (Gladwin 1978). Also, when one noise is much greater than another, the addition of the lesser noise typically adds an almost undetectable amount to the overall decibel level. For example, the addition of one F-15 taking off with a B-52 would not likely increase the detectable sound pressure level generated by the one operating alone.
In addition to sound pressure level, any noise event also has a characteristic pitch, a distribution of sound pressure as a function of frequency. Pitch is a measure of how often these fluctuations repeat during a given period, usually 1 second. Although human response to noise is strongly dependent on frequency, the frequency/response correlation is not known for the majority of wildlife species. The audible frequency range for the average human varies from about 20 Hz (Hertz, i.e., cycles per second) to about 16,000 Hz (16 kHz). In general, people are less sensitive to low-frequency noise (e.g., 100 Hz), than they are to high-frequency noise (e.g., 2 kHz). Domestic sheep are most sensitive to frequencies around 7 kHz (Figure 1).
Pure tone sound (e.g., sound produced by a tuning fork) consists of a single frequency. Aircraft-generated sound is much more complex in frequency structure; each specific aircraft type produces noise extending over a wide frequency range. The narrow-band pure tone whine of a jet engine compressor is readily recognizable above the broad-frequency noise of the jet engine exhaust stream. Each type of aircraft engine and aircraft operating environment produces a characteristic frequency spectrum, which is usually measured in octave bands, either frequency-weighted or one-third octave. The overall noise level, known as the overall sound pressure level, is calculated by summing the sound levels in each octave band, or partial octave band, according to the rules of decibel addition.
Not only is the human ear (and the ears of some other animals) more sensitive to high frequencies than to low frequencies, but also the sensitivity of the human ear to sound of varying frequencies changes with the magnitude of the sound (Figure 2). A technique for relating physical noise properties and measurements to the subjective response of various species is desirable, but rarely attainable. The introduction of noise frequency weighting on sound-level meters is one attempt to solve this problem for human noise impact assessment. However, no such device has been developed for a species of wildlife or domestic animal.
One widely used frequency weighting system is known as the A-weighting network and has been standardized in current sound-level meter specifications (Peterson and Gross 1972). The A-weighting system assigns low weights to the low-frequency tones, to which the human ear (and the ears of some other animals) is less sensitive, and high weights to the typically more audible high-frequency tones. The A-weighting noise analysis technique correlates well with human response to noise. A drawback to its use, however, is that a simple sound level measure usually does not adequately account for this tonal
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Figure 1. Plot of minimum audible field with decibels shown as sound pressure level above background (26 dB) (Ames 1978).
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Figure 2. Pure-tone frequency response of the human ear (Peterson and Gross, 1972)
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component effect. In the A-weighting system, a noise subjectively judged to be twice as loud as another sound would have an A-weighted value approximately 10 dBA greater than the first sound, even though this change corresponds to a factor of 10 in actual sound level.
Turbofan and turbojet engines are major sources of intense aircraft noise. Although turboprop-powered aircraft also are used by the U.S. Air Force, their contribution to the overall noise environment is of relatively minor importance compared to jet-powered aircraft. Jet engines are generally more powerful and produce noise of higher magnitude than turboprop or piston aircraft engines. Also, jet engines produce a greater amount of noise in the high-frequency range, thus increasing their relative annoyance factor.
In jet-powered aircraft, the primary sources of engine noise are the roar of the jet exhaust stream and the high pitched noise generated by the engine's turbo-machinery, compressor, and blades. The exhaust roar is created by the rapid expansion of high-velocity exhaust gases.
In general, the amount of noise generated by a jet aircraft engine is proportional to its exhaust stream velocity raised to the eighth power. By forcing atmospheric air into the jet engine intakes, the average velocity of the exhaust stream is reduced, decreasing the resultant noise intensity. For this reason, turbofan aircraft engines produce less noise at the same power setting than turbojet engines. The fan ducts of turbofan aircraft engines create a secondary air flow around the exhaust stream, thereby decreasing noise levels by reducing the magnitude of the shearing gradients between exhaust core and the ambient atmosphere. The higher a turbofan engine's bypass ratio, the less noisy its operation. The use of after-burners in military aircraft creates the opposite effect; the velocity of the exhaust stream is increased, thereby increasing the noise level.
Other jet engine noise sources are readily apparent, and may even be dominant during stationary or low-speed ground operations. The high-frequency whine of the engine's fans and compressors tend to be particularly annoying to most human listeners, and possibly to most animals. High bypass-ratio fan jets are quieter because their engines have slower fan speed, nacelle duct lines with acoustically absorbent material, and no inlet guide vanes.
The loudest noise generated by piston- or turbine-powered propeller aircraft generally occurs during takeoff, when the engine is operated on a high power setting. This noise is composed of a wide range of frequencies, but the major portion is at the lower end of the frequency spectrum. The turboprop engine is typically quieter than the piston engine during takeoff, but the compressor has the high-frequency whine, similar to jet engines.
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During supersonic flight, the shock waves generated from forward-facing portions of an aircraft are usually regions of positive overpressure. The waves originating from rear surfaces of the aircraft are typically regions of negative overpressure, or underpressure. The pressure signature is the variation in overpressure generated by the forward- and rearward-facing surfaces of an aircraft flying at supersonic speed, creating the sonic boom (Figure 3). As an aircraft reaches supersonic flight, the pressure signature is propagated along a path commonly referred to as the sonic boom ray (ray AC, Figure 4); the presssure signature is generated at the point on the flight line from which the sonic boom ray emanates (point P, Figure 4).
The sonic boom rays emanating from an aircraft operating at supersonic speed initially form a cone (Figure 4). However, due to atmospheric variations (e.g., wind and temperature gradients) the rays conform to the laws of atmospheric refraction and become horn-shaped, forming a boom conoid (Figure 5). Because all relevant refraction properties of the atmosphere are usually not known, developing an accurate boom conoid for a given supersonic flight event is difficult.
In the absence of winds, the increase in the speed of a sonic boom along a descending ray creates a decrease in the ray angle (Peterson and Gross 1972). For this reason, a boom ray tends to be refracted upward, away from the ground. Due to this phenomenon, angles from the vertical of two boom rays from each point on a supersonic flight path are sufficiently great that the boom rays only graze, or do not reach, the ground. The sonic boom "carpet" (the area on the ground that experiences the sonic boom) is defined by the locus of points of the boom rays that just graze the ground (Figure 6). Surface areas outside these points experience no sonic boom.
A tail wind behind an aircraft enhances the effect of the increase in sound speed. A head wind creates the opposite effect and tends to refract the boom rays toward the ground. Also, the paths of propagation of the atmospheric pressure disturbances depend on the manner the aircraft is flown, as well as on the prevailing atmospheric conditions.
Under certain aircraft operating conditions (e.g., acceleration, dives, turns, and climbs), the sonic boom conoids generated by the aircraft may intersect one another. This effect is known as sonic boom focusing. Such focusing may also result from refraction effects caused by variations in atmospheric sound and wind speed. Focused sonic booms may be of much greater intensity than unfocused booms and are typically generated by fighter aircraft in "dogfight" maneuvers.
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Figure 3. Characteristics of a sonic boom; pressure (vertical axis) plotted against time (horizontal axis) (Cottereau 1978).
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Figure 4. Vertical section of sonic boom cone (Peterson and Gross 1972).
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Figure 5. Refraction of boom rays as they pass down from an aircraft to the ground (Peterson and Gross 1972).
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Figure 6. Sonic boom carpet from supersonic flight (Peterson and Gross 1972).
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The propagation of aircraft noise and sonic boom from source to receiver is a function of several factors, including relative distance; atmospheric attenuation due to wind, humidity, and temperature; and intervening noise barriers (e.g., large stands of trees and buildings). The distance relationship is relatively straightforward; as acoustic energy spreads out over an increasingly larger area, the amount of sound energy per unit volume of atmosphere steadily decreases. For subsonic noise, this decrease is inversely proportional to the square of the distance between the aircraft and the receiver (i.e., a decrease in acoustic intensity of approximately 6 dB for each doubling in relative distance).
Atmospheric conditions affect noise propagation. Water vapor in the atmosphere is relatively effective at absorbing noise. Also, the higher noise frequencies are more readily absorbed. For this reason, high-frequency noise typically decreases with distance more rapidly than does either midrange or low-frequency noise. For aircraft in flight, air absorption has the greatest influence on noise propagation.
Atmospheric temperature gradients also affect aircraft noise propagation. During periods of normal temperature gradients, where air temperature steadily decreases with increasing altitude, aircraft noise is, for the most part, deflected upward, thereby producing areas of little or no noise on the ground at certain distances from the aircraft. During periods of atmospheric temperature inversion, the reverse situation is true and aircraft noise tends to be deflected downward, thus increasing ground noise level (Gladwin 1978).
During low-level aircraft operations, surface absorption and deflection may decrease the observed noise levels at low angles of observation. Intervening objects (e.g., hills, buildings) will also affect noise propagation.
Aircraft noise reduction measures may include modification of the: (1) noise source, (2) noise pathway between the source and the receiver, or (3) receiver. Although reducing aircraft noise at its source may seem the most expedient method of noise reduction, it generally cannot be done with military aircraft because of their high performance demands. This is especially true of combat aircraft. Use of acoustically modified jet aircraft engines has resulted in some reduction in aircraft-generated noise; however, development of economically feasible, quieter aircraft engines has proven to be a relatively slow process.
Modification of the noise pathway through the use of natural or artificial acoustic barriers has been used to interrupt the acoustical line-of-sight between the aircraft and receiver. Such interruption usually is restricted to locations close to air bases exposed to noise from numerous ground operations. Hills or woodlands can sometimes effectively shield nearby areas from aircraft ground operations, especially when such noise barriers are located close to the noise source. A relatively large area of dense, tall woodland is required before such vegetation has a significant noise reduction effect.
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The effects of noise and sonic booms on animals vary due to the animal's hearing ability, which varies considerably among animal species. Each species has adapted, physically and behaviorally, to fill an ecological role within a community; an animal's hearing ability often reflects this role. Animals rely on hearing to avoid predators, to obtain food, and to communicate with members of their own species and other members of the community.
If sound has been a determinant in the evolution of behavior and morphology, its production and use have also depended on other aspects of the external environment (Bogert 1960). While specializations such as echolocation entail an integrated evolution of mechanisms of sound production and sound reception, the evolution of one is not always dependent on the evolution of the other. Sound production is not confined to animals with well-developed sound receptors, nor do all animals in which sound perception is well-developed produce sound themselves.
Sound production by animals also varies considerably. For example, mammalian vocalizations range in frequency from 50 to 100 Hz in the horse up to 150 kHz in some bats (Gould 1983). High-frequency sounds are extremely directional and attenuate quickly with distance. Low-frequency sounds attenuate slowly with distance and are relatively omnidirectional. The transmission properties of a vocalization depend on environmental factors, such as temperature, humidity, landscape, and vegetation. Range of vocal signal is influenced by intensity of the source, background noise levels, rates of signal degradation, and the perceptual abilities of the receiver (Gould 1983). Vocal communication in social animals helps maintain group cohesiveness by giving cues to individual identification and the next possible action of group members (Kiley-Worthington 1984). Noise impacts could potentially disrupt a species' ability to communicate, either vocally or by disturbing its behavioral patterns.
The literature concerning hearing ability of animals includes studies of hearing mechanisms and determination of hearing thresholds (audiograms), through primarily behavioral responses to various noise levels in laboratory experiments. Knowledge of specific audiograms for even domestic species is scant; however, a number of studies have been conducted since the mid-1970's on the hearing ability of various wildlife species. Comparisons between groups of species within the same habitat have revealed a wide variety of tolerance to noise levels.
Noise affects wildlife and other animals, including humans, in many ways. Janssen (1980) categorized these effects as primary, secondary, or tertiary. Primary effects are direct physical auditory changes, such as eardrum rupture,
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temporary and permanent hearing threshold shifts, and the masking of auditory signals. Basking is the inability of an animal to hear important environmental signals. These signals include noises made by potential mates, predators, or prey. Aircraft noise could conceivably cause masking of the signals in some species and populations of wildlife. Secondary effects of aircraft noise and sonic booms on wildlife include such nonauditory effects as stress, behavioral changes, interference with mating, and detrimental changes in the ability to obtain sufficient food, water, and cover. Tertiary effects are the direct result of both primary and secondary effects, and include population declines, destruction of important habitat (Klein 1973), and, in extreme cases, potential species extinction (Bender 1977).
Animal species differ greatly in their response to noise of various characteristics and duration. Individual animal response to a given noise event or series of events also can vary widely, due to a variety of factors, including time of day and year, physical condition of the animal, physical environment (such as whether the animal is restrained or unrestrained), the experience of the individual animal, and whether or not other physical stressors (e.g., drought) are present.
The effects of noise on the physiology of laboratory animals have been studied more thoroughly than effects on farm animals or wildlife. Although laboratory studies cannot be directly applied to effects of noise on wildlife in their natural habitats, they do describe a range of potential effects that may possibly occur. Hearing sensitivity, susceptibility to noise-induced hearing loss, and physiological effects of noise vary among animal species. Animals appear to be more sensitive to noise disturbance than humans (Borg,1981). Possible harmful effects of sound may be more related to information content of the sound--information pertaining to risky actions or masking significant information--rather than to sound itself.
A sudden or unfamiliar sound is believed to act as an alarm, activating the sympathetic nervous system. The short-term physiological stress reactions, referred to as "fight-or-flight," are similar for many vertebrate species (Holler 1978). Various stimuli can produce similar physiological effects. Different stressors have their own unique effects, however, and reactions to stress can vary between species and also among individuals of the same species. 0nly laboratory studies have been able to eliminate these variables and show that noise produces certain physiological effects.
The general pattern of response to stress includes activation of the neural and endocrine systems, causing changes such as increased blood pressure, available glucose, and blood levels of corticosteroids. The effect of sympathetic activation on circulation also is believed to have an effect on hearing (Holler 1978). A correlation has been shown to exist between the reaction on the peripheral circulation and the temporary threshold shift caused by noise exposure. Prolonged exposure to severe stress may exhaust an animal's resources and result in death.
The introduction of commercial and military supersonic aircraft has raised the question of whether sonic booms should be considered as severe environmental pollution, with adverse effects on humans, animals, and
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structures (Cottereau 1978). Reviewers of Air Force proposals for new low-altitude training routes and military operating areas frequently express concern regarding the effect of jet noise on wildlife and farm animals (Shotton 1982). Differences in noise from low-altitude subsonic overflight and high-altitude supersonic overflight include the increased duration of noise from a low-altitude overflight, the greater probability that noise from low-altitude overflights will be accompanied by visual perception of the aircraft, and the broad-band frequency distribution of jet engine noise (about 200-20,000 Hz) versus the low-frequency noise of sonic booms (with most of the sound energy between 15-50 Hz).
Much of the knowledge in the past concerning effects of sonic booms was based on occasional booms, many of which had resulted in complaints and claims (Boutelier1968; Bond 1971; Milligan et al. 1983). Although probably not always legitimate, these complaints indicate that concern has developed about the effects of sonic booms, and this concern should stimulate intensified research. However, only a few investigations, under field or simulated conditions, have been undertaken to determine the possible effects of sonic booms. The few documented behavioral observations of animals appear to indicate that sonic booms and subsonic low-altitude-flight noise evoke startle reactions; however, specific reactions differ according to the species involved, whether the animal is alone, and perhaps whether the animal has been previously exposed to sonic booms (Bell 1972). Some animals appear to adapt to the disturbances. Avian species seem to be more affected than mammals.
Trampling, moving, raising the head, stampeding, jumping, and running are among the common reactions reported for mammals exposed to sonic booms (Bell 1972). Birds occasionally run, fly, or crowd. Reactions vary from boom to boom and do not appear to be predictable. Animal reactions to sonic booms are similar to their reactions to low-altitude subsonic airplane flights, helicopters, and sudden noises.
Aircraft noise and sonic booms have been implicated as a cause of lowered reproduction in a variety of animals. The majority of research on the reproductive effects of noise on animals has been conducted in the laboratory with domestic species, particularly poultry. However, field studies indicate that the reproduction of wild populations may be more affected by noise disturbance than domestic populations. The reproductive effects have primarily been the result of disturbance of the animal's behavior during the reproductive cycle.
In the following sections, literature concerning animal hearing and the effects of aircraft noise and sonic booms on various groups of animals is presented. Some information concerning other types of noise is also included, to supplement the lack of knowledge on the effects of aircraft noise. These sections serve to summarize the literature, not to evaluate the appropriateness or adequacy of the scientific approach of each study.
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The sense of hearing has become highly developed and specialized in the mammals relative to other tetrapods (Stebbins 1978; Harrison 1984). Increases in absolute sensitivity to acoustic stimuli in the audible frequency range and enhanced differential acuity to auditory stimuli, such as frequency and intensity, have contributed to the success of the mammals as a group. Evolutionary changes in the structure of the middle ear conducting system, in the cochlea, and, to a lesser extent, in the central nervous system are presumed responsible for the highly developed sense of hearing. The considerable variation in auditory capabilities in the various Orders and Families of mammals reflects the different selective pressures that have played a major role in hearing development. In some mammals, orientation and navigation have emphasized extended high-frequency sensitivity, while in others the obvious adaptive value of tightly knit social organization has placed a premium on the fine discrimination of the small, but significant, changes in the acoustic patterning of intraspecific communication sounds.
The basic characteristics of hearing, communication, and orientation signals were investigated in 30 species of insectivores (e.g., moles, shrews), bats, and marine mammals. The sensitivity of hearing, range of reception, and time parameters were found to be distinctly dependent on ecological factors and the acoustics of the environments of the animals under study (Konstantinov 1978). Animals with exclusively underground life habits (e.g., moles) show hearing of the lowest frequency and relatively high thresholds. A considerable extension of the reception range into the ultrasound frequency zone, with a lowering of the thresholds and more rapid response to the subsequent acoustic signals, was ascertained in species of largely nocturnal life habits. The acoustic system is most refined in animals using ultrasound echolocation for orientation and searching for prey in a tridimensional space, under optically unfavorable conditions (e.g., bats, porpoises).
Sound levels above about 90 dB are likely to be adversive to mammals and are associated with a number of behaviors such as retreat from the sound source, freezing, or a strong startle response. Sound level below about 90 dB usually cause much less adversive behavior. Laboratory studies of domestic mammals have indicated that behavioral responses vary with noise types and levels, and that domestic animals appear to acclimate to some sound disturbances (e.g., Anthony et al. 1959; Bond et al. 1963; Ames and Arehart1972; Espmark et al. 1974; Ames 1978).
Host studies on the effects of noise and sonic booms on mammals have been conducted on laboratory animals (Table 2). However, field studies, primarily investigating behavioral effects, have been conducted on several species of wild mammals.
Surprisingly, the hearing of livestock has not been investigated, with the exception of a few studies that determined auditory thresholds of Suffolk ewe lambs (Ames and Arehart 1972; Ames 1978) and cattle (Ames 1974). The threshold curve of the lambs declined gradually from 100 to 500Hz, then
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Table 2. Some possible negative effects of noise and sonic booms on animals.
Species |
Type of noise |
Effect |
Domestic livestock: |
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|
|
Various species |
Sonic boom (80-370 mN/m2); low-level subsonic flights (50-200 m) (Nixon et al. 1968; Bond et al. 1974; Espmark et al. 1974). |
Startle reaction |
|
Dairy cow |
Exploding paper bags (Ely and Petersen 1941) |
Cessation of milk ejection |
|
|
General noise (105 dB) (Kovalcik and Sottnik 1971) |
Reduces feed consumption, milk yield, and rate of milk release |
|
|
Tractor engine sound (97 dB) (Broucek et al. 1983) |
Increased glucose concentration and leukocyte counts in the blood; reduced level of hemoglobin |
|
|
General noise (1 kHz, 110 dB) (Broucek et al. 1983) |
Increase in glycemia, nonesterified fatty acids, creatin; decrease in hemoglobin and, thyroxin concentration |
|
Goat |
Jet noise (Sugawara et al, 1979) |
Reduced milk yield |
|
Swine |
General noise (108-120 dB) (Borg 1981) |
Influence on hormonal system: increase of plasma 11-OH-corticosterone and catecholamines; decreased corticosteroid level |
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|
General noise (93 dB) (Dufour 1980) |
Aldosteronism (excess secretion of aldosterone from the adrenals) |
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|
Recorded aircraft noise (120-135 dB) (Bond et al. 1963) |
Increased heart rate |
|
Sheep |
White noise (100 dB) (Ames and Arehart 1972) |
Higher heart rate and respiration rate; lower feeding efficiency |
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|
White noise (90 dB) (Ames 1978) |
Decreased thyroid activity |
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|
General noise (4 kHz, 100 dB) (Ames 1978) |
Increased number of corpora lutea; more lambs/ewe |
Wild ungulates: |
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|
|
Reindeer |
Sonic booms (35-702 Pa) (Espmark 1972) |
Slight startle responses: raising of head, pricking the ears, scenting the air |
|
Caribou |
Low-altitude aircraft (<200 ft): fixed-wing, helicopter (Klein 1973) |
Running and panic behavior |
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|
Low-altitude aircraft (<500 ft): fixed-wing, helicopter (Calef et al. 1976) |
Escape or strong panic reactions |
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|
General noise (Calef 1974) |
Increased incidence of miscarriages; lower birth rates |
|
Pronghorn |
Low-altitude helicopters (150 ft, slant range of 500 ft; 77 dBA) (Luz and Smith 1976) |
Running |
Laboratory rodents and rabbits: |
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|
|
Various species |
General noise (150 Hz-40 kHz, 132-140 dB) (Anthony and Ackerman 1957) |
"Anxiety-like" behavior |
|
Guinea pig |
General noise (128 dB SPL) (Beagley 1965); simulated sonic booms (130 dB) (Hajeau-Chargois et al. 1970) |
Anatomical hearing damage; hearing loss |
|
Mouse |
Simulated sonic booms (Reinis 1976) |
Auditory damage; inner ear bleeding |
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|
Intermittent noise (l10 dB) (Anthony and Ackerman 1955) |
Decrease in circulating eosinophils; adrenal activation |
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|
Recorded subway noise (105 dB SPL) (Busnel and Holin 1978) |
Longer time interval between litters; lower weight gain of young; increased incidence of miscarriage, resorption and malformations |
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|
Continuous, high-intensity jet engine noise (127 dB); random onset noise (103-ll0 dB); high-frequency noise (l13 dB) (Nawrot et al. 1980) |
Decreased pregnancy rate (all groups); decrease in number of implantation sites per litter and fetolethal effects (high-intensity jet noise) |
|
|
General noise (106 dB) (Ishii and Yokobori 1960) |
Teratogenic effects |
|
Rat |
General noise (105 dB SPL) (Moller 1978; Borg 1979, 1981) |
Hearing loss; damage to inner ear structure |
|
|
General noise (80 dB SPL) (Borg 1978a,b,c) |
Vasoconstriction |
|
|
General intermittent sound (Buckley and Smookler 1970) |
Rise in blood pressure; hypertension |
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Recorded thunderclaps (98-100 dB SPL, 50-200 Hz) (Ogle and Lockett 1966) |
Increased urinary excretion of sodium and potassium; excretion of oxytocin and vasopressin |
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Electric buzzer (110 dB) (Sackler et al. 1959) |
Decreased adrenal , body, thymus, spleen, liver, pituitary, ovary, and uterine weights; slight gain in thyroid weight; increased production of ACTH; inhibition of gonadotrphin, ovarian hormones, and possible inhibition of the thyrotrophic and thyroid hormones |
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General noise (1 kHz, 95 dB) (Fell et al. 1976) |
Suppressed thyroid activity |
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General noise (120 Hz, 95-105 dB) (Jurtshuk et al. 1959) |
Reduced glutathione levels in blood, increased adrenal weights and ascorbic acid; decrease in total adrenal cholesterol |
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Intermittent noise(95 dB)(Hrubes and Benes 1965) |
Increased secretion of catecholamines in the urine; increased free fatty acids in the blood plasma; increased weight of the adrenals; inhibition of growth |
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General noise (92 dB) (Gamble 1982) |
Persistent vaginal estrus prolonged vaginal cornification; higher preweaning mortality of young |
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White noise (102-l14 dB) (Friedman et al. 1967) |
Change in the hypothalymus |
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Electric bell (95-100 dB) (Zondek and Isacher 1964) |
Enlarged ovaries; persistent estrus; follicular hematomas |
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General noise (Zondek 1964) |
Decreased fertility |
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Domestic rabbit |
White noise (107-112 dB) (Nayfield and Besch 1981) |
Increased adrenal weights; decreased spleen and thymus weights |
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White noise (102-114 dB) (Friedman et al. 1967) |
Change in the hypothalymus; higher plasma cholesterol and plasma triglycerides; fat deposits in the irises of the eyes; more aortic atherosclerosis and higher cholesterol content in the aortas |
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Electric bell (95-100 dB) (Zondek and Isacher 1964) |
Enlarged ovaries; persistent estrus; follicular hematomas |
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Chinchilla |
Simulated sonic booms; general noise (65-105 dB) (Carder and Miller 1971, 1972; Reinis 1976) |
Hearing loss; outer cell damage of the cochlea |
Wild rodents: |
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Desert kangaroo rat |
ORV noise (78-110 dB SPL) (Brattstrom and Bondello 1983) |
Temporary threshold shift in hearing |
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House mouse (feral) |
Aircraft (110-120 dB) (Chesser et al. 1975) |
Increased adrenal weights |
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Cotton rat |
Recorded aircraft noise (110 dB SPL) (Pritchett et al. 1978) |
Increased body weights; increased secretion of ACTH |
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High-pitched whistles (Hepworth 1966) |
Enlarged ovaries; persistent estrus; follicular hematomas |
Carnivores: |
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Domestic cat |
Noisy laboratory (Liberman and Beil 1979) |
Hearing threshold shifts; loss or damage to hair cells of inner ear |
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General noise (100-1,000 Hz) (Miller et al. 1963) |
Hearing threshold shifts |
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Domestic dog |
Sudden loud noises (Stephens 1980) |
Increase in plasma corticosteroid concentrations |
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Farm-raised mink |
Simulated sonic booms (167-294 mN/m2) (Travis et al. 1974) |
Brief startle reaction |
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Wolf/grizzly bear |
Low-altitude fixed-wing aircraft and helicopters (Klein 1973) |
Startle reaction; running |
Aquatic mammals: |
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Beluga whale |
Boat traffic (Acoustical Society of America 1980) |
Easily displaced |
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Pinnepeds |
Sonic booms (80-89 dBA SPL) (Jehl and Cooper 1980) |
Startle reactions |
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Elephant seal |
Impulse noise created by a carbide pest control cannon (115.6-145.5 dBA) (Stewart 1982) |
Alert behavior |
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Sea lion |
Simulated boom (Stewart 1982) |
Left beach during non-breeding season and went into surf |
other mammal groups: |
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Rhesus monkey |
General noise (Leq (24): 85 dB) (Peterson et al. 1981) |
Increased blood pressure |
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decreased rapidly and reached its lowest point at 7,000 Hz. The audiogram for sheep was similar in shape to that for humans, but at a higher frequency (most sensitive at 7,000 Hz). Significant differences were observed among individual sensitivities at different frequencies, with the lower frequencies exhibiting large variations. Therefore, response to sound stimuli can be expected to vary among individuals within a species.
Behavior reactions observed in livestock exposed to sonic booms (80-370 Pa) or low-altitude subsonic flights (50-200 m) have generally consisted of startle reactions that were considered minimal (Nixon et al, 1968; Bond et al. 1974; Espmark et al. 1974). Espmark et al. (1974) suggested that observed reactions (e.g., backward jumping) may be more dangerous for tied-up animals, and that the effects of these disturbances might be more severe for animals under certain physiological conditions, such as gestation.
The use of military aircraft at supersonic speeds has already resulted in damage claims being made (and in some cases, being paid) for alleged injury or losses in domestic livestock (Ewbank 1977). This has prompted a number of investigations of the effects of noise on domestic farm animals, including the physiological effects of aircraft and nonaircraft noise on dairy cows, goats, pigs, and sheep.
0ne of the earliest studies of noise effects on cows was an attempt to determine the relationship between the nervous system and the ejection of milk of three Jersey cows at the Kentucky Agricultural Experiment Station (Ely and Peterson 1941). The left half of the udder of each cow was denervated. After recovering from surgery, all three cows began ejecting milk normally. The denervated half of the udder was able to eject milk just as well as the intact half. 0ne cow was then subjected to various experiments to determine the effect of the nerve supply to the glands under various conditions, such as fright caused by loud noises. Fright was induced by exploding paper bags every 10 seconds for 2 minutes just prior to attaching the mechanical milker. This resulted in an immediate cessation of milk production. Thirty minutes following exposure to exploding paper bags, 70% normal milk production occurred. No difference in response between the two halves of the udder was observed. Injections of adrenalin gave similar results. The amount of adrenalin injected appeared to determine the length of time needed before natural milk ejection resumed. Presumably, this length of time would be proportional to degree of fright. Fright, such as that caused by a loud sound, could stimulate the natural production of adrenalin.
Parker and Bayley (1960) studied the effects of jet aircraft noise and flyovers on milk production of dairy herds located near existing air bases. Data for 12 months were compiled on the daily milk deliveries of 182 herds located within 3 miles of eight Air Force bases. Although data were lacking at some bases, results of this survey showed no evidence of effects on milk production resulting from jet overflights or proximity to an air base. Milk yield of dairy cows in an area of frequent sonic booms, Edwards Air Force Base, California, was also similar to the yield of control dairy cows; however, the animals had been previously exposed to at least four to eight sonic booms per day prior to data collection (Casady and Lehmann 1967).
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Bond et al. (1974) found no evidence that simulated sonic booms had any effect on eating patterns, total feed intake, or rate of feed intake in dairy cows. However, Kovalcik and Sottnik (1971) found that a noise level of 80 dB (unspecified scale) increased feed intake and the rate of milk-releasing indices, but did not affect the milk yield of dairy cows. (The everyday noise level of the animals' surroundings was 50-60 dB.) Kovalcik and Sottnik (1971) presumed that the noise level of 80 dB was within the limits of the normal tolerance of the animal. When these same animals were exposed to a sudden high-intensity noise (105 dB), feed consumption was reduced as well as milk yield and rate of milk release. The authors found, however, that if the noise is increased gradually, instead of suddenly exposing the animals to the high-intensity noise, the response is not as negative.
Tractor engine sound at 97 dB significantly increased the glucose concentration and leucocyte counts in the blood of dairy cows and markedly reduced the level of hemoglobin (Broucek et al. 1983). An experiment using a tone of 1,000 Hz (l10 dB) resulted in a significant increase in circulating glucosea, nonesterified fatty acids, and creatin; a significant decrease in hemoglobin; and a slight decrease in thyroxin in plasma. High glucose level is a recognized response to stress, in this case, probably sound. The accompanying responses were also the result of stress, and part of the neuroendocrine stress reaction. For example, release of thyroid stimulating hormone (TSH), known to affect growth rates, can be inhibited by negative feedback from adrenocortical hormones after a stress response.
Cottereau (1978) stated that simulated sonic booms had no effect on semen quality or quantity of bulls at an artificial insemination center. Pregnant Charollais cows exposed to 20 simulated sonic booms during the first month of pregnancy gave birth to normal calves. The intensity and frequency of the booms was not described.
Noise (including jet noise) reduced the milk yield in all five goats used in an experiment (Sugawara et al. 1979). The noise had a greater effect on milk yield within the first 3 months after parturition. Sugawara et al. (1979) suggested that intermittent exposure to noise had a greater effect than continuous exposure.
Pigs exposed to120-dB sound for 6 hours showed an increase of plasma 11-OH-corticosterone and catecholamines (Borg 1981). Exposure to 108-dB engine sound for 72 hours resulted in a decreased corticosteroid level, followed by an increase immediately after the stimulation ceased. This biphasic response may indicate a negative feedback effect on the anterior pituitary, which is responsible for releasing ACTH that activates the adrenals during stress. Sound exposure, at least short-term, influences several hormonal systems of pigs.
Excess secretion of hormones from the adrenals, water retention, and sodium retention were observed in castrated male pigs exposed to 93-dB (unspecified frequency) continuous noise over several days (Dufour 1980). Excess aldosterone may be induced by stress, resulting in the upset of the electrolyte balance, which can be manifested by hypertension (possibly due to sodium and water retention), excessive urination, and thirst (Dufour 1980).
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Bond et al. (1963) studied noise effects on feeding efficiency and weight gain of pigs by exposing three to five groups of four to six pigs to recorded aircraft noise at 120-135 dB for 12 hours daily, from weaning to slaughter at 200 pounds body weight. No significant differences between the noise-exposed pigs and controls were observed for rate of feed utilization; rate of weight gain, or food intake, nor was there injury or anatomical change to the organ of Corti of the inner ear.
Heart rate of a large number of weaned pigs was measured before, during, and after sound exposure (Bond et al. 1963). A telemetering electrocardiograph that records heart rate was used to eliminate possible effects of human presence. After a constant heart rate was observed, the experiment was begun. Test recordings of heart rate were made during 15 seconds of prestress, 15 seconds of noise exposure, and 30 seconds of quiet recovery period. Heart rate increased significantly during sound exposure, but decelerated rapidly after the sound was discontinued, although not to baseline rate. No evidence of cochlea injury was found in any of the animals. Histological examination of the thyroid and adrenal glands indicated no evidence of impaired function. Under the conditions of the study, no evidence was found that the pigs were significantly affected by noise. The temporary increase in heart rate was the only indication that noise caused stress.
Pigs, boars, and sows were exposed to reproduced aircraft noise and other loud sounds to determine possible harmful effects on reproduction (Bond et al. 1963). The tape recording consisted of propeller-driven aircraft, jet aircraft in flight, and airfield background noises. The animals were exposed to sound frequencies varying from 100-120 dB. The conception rate of sows exposed to the recorded sounds was similar to that of unexposed sows. The number of pigs farrowed and the number of survivors were not influenced by exposure of the parents to loud sound during mating, or by exposure of sows to reproduced sounds at120 dB for 12 hours daily, beginning 3 days before farrowing and continuing until their piglets were weaned.
The initial physiological responses to sound measured in sheep were heart rate and respiratory rate (Ames and Arehart 1972). Early-weaned lambs were exposed to three sound types: (1) United States of America Standard Institute white noise, (2) instrumental music, and (3) intermittent miscellaneous sound (IMS). Each sound type was studied at two sound pressure levels, 75 and 100dB. The IMS consisted of the following sounds: electrical and diesel engines, jet and propeller aircraft, roller coasters, stadium noise, fog horns, firecrackers, machine guns, cannons, rain, and band marches. White noise and music exposures were continuous. The control period was 21 days with a background noise level of 45 dB. Initial exposure to 75- and 100-dB white noise did not cause a change in heart late in acclimated lambs. In nonacclimated lambs, initial exposure to 100-dB white noise significantly increased heart rate. During the entire test period, nonacclimated lambs exposed to 100-dB white noise had significantly higher heart rate than lambs acclimated at either 75 or 100 dB.
Respiration rate for acclimated lambs was constant when initially exposed to 75 d8, increased rapidly during the first hour, and peaked during the eighth hour. Nonacclimated lambs showed little change in respiration rate
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until the fourth hour, when a rapid increase occurred. After 8 hours of exposure to 100 dB, both acclimated and nonacclimated lambs had significantly higher respiration rates than controls and lambs exposed to 75 dB. This trend continued for the 12-day test period. Initial exposure to music at 75 dB increased the heart rate. Acclimated lambs exposed to 100 dB music had significantly higher heart rate over the 12-day period compared to lambs exposed to 75 dB. Nonacclimated lambs had significantly higher heart rate than acclimated lambs subjected to both 75 and100 dB. Nonacclimated lambs exposed to 100 dB IMS had significantly higher heart rates than acclimated lambs; however, respiration rates were highest at 75 dB.
Data presented in Ames and Arehart's (1972) study indicated that some physiological responses to sound were characteristic of those of the stress response (e.g., adrenally oriented responses and acclimation to the sound environment). A sudden change that startled an animal usually resulted in tachycardia through action of catecholamines, or bradycardia caused by vagal stimulation. Sound exposures also usually resulted in vagal stimulation, except for nonacclimated lambs exposed to 100-dB white noise. Heart rate response varied less when exposed to music, which suggests that music is less stressful than other sound types. Responses apparently varied by sound pressure level and duration. Respiratory rate appeared to be dependent on sound type (continuous rise in rate during IMS exposure) rather than sound level, with a possible effect of intermittent play versus continuous exposure.
Arehart and Ames (1972) also determined the effect of sound types and intensities on growth and feeding efficiency on early-weaned lambs. Sixty lambs were exposed to the same three sound types and intensities (75 and 100 dB) of the above experiment. White noise at 75 dB significantly increased the average daily weight gain and feeding efficiency. Acclimated and non-acclimated lambs subjected to 100-dB white noise had significantly lower feeding efficiency, which was still higher than the feeding efficiency during the control period. Music at either intensity had no significant effect on performance. Lambs subjected to IMS noise consumed less feed per day than lambs exposed to 75 dB white noise or music. Average daily gain in weight was significantly higher at 75 dB compared to controls and 100 dB IMS exposure.
The pooled data from Arehart and Ames's (1972) experiments indicated that intensity of sound significantly affected growth rate in early-weaned lambs. Again, music was less stressful than other sound types. The data also suggested that acclimation to sound occurred, with respect to daily growth rate. All nonacclimated lambs exposed to 100 dB noise gained significantly less weight than lambs previously exposed to 75 dB noise, suggesting that long-term study is needed to determine whether detrimental effects would actually occur during long-term feeding trials.
Harbers et al. (1975) studied the digestive response of yearling wethers to the same sound types and intensities used in the two studies above: white noise and music presented continuously and IMS. In control metabolism trials, sheep were placed in metabolism crates and exposed to 45 dB background noise for 14 days. Dry matter feed intake was less when sheep were exposed to 75 or 100 dB of each sound type compared to controls. Type of sound had no effect on feed intake. Water intake and urinary output appeared to depend on sound
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type and not intensity. Sheep exposed to IMS consistently drank more water and excreted more urine than sheep exposed to continuous sounds, white noise, or music. If intermittent sounds are more annoying than continuous noise, this might explain why these lambs drank more water. Sound level, type, and the interaction of these influenced fecal moisture. Lambs exposed to 100-dB music or IMS had less fecal water. Music at 75 dB resulted in more fecal water excreted in those lambs, and less when exposed to 75 dB white noise and IMS. However, fecal water was not related to water intake.
Exposure to IMS at 75 and 100 dB not only increased water intake, but also increased metabolizable energy of the ration and improved the apparent nutrient digestibilities. Sound intensity did not affect apparent digestibility coefficients. The high digestibility coefficients for lambs exposed to intermittent sounds suggests that those types of auditory stimuli influenced the digestive system. This increased digestibility of feed, along with water retention, may partly explain the improved growth gain in lambs exposed to IMS. IMS increased metabolizable energy by 100 Kcal/day; no effect of intensity was observed.
Sheep probably acclimated to continuous and intermittent sound of 100 dB or less. None of the sound stimuli seemed to adversely affect digestibility, with intermittent sound actually stimulating digestion. All of the above mentioned effects were short-term only. The effect of intermittent sound on long-term feed intake and digestibility should be investigated. The increased metabolic rate, had it continued, may have proved detrimental to the animal by shortening its life span or causing other physiological changes. Noise exposure above background level may play an important role in digestive efficiency, metabolic balance, and growth rate.
Ames (1978) studied the effects of sound on the endocrine function of sheep. Thyroid activity of 100 lambs exposed to 75-dB and 90-dB white noise was measured and compared to controls. After 14 days of noise exposure, serum samples were collected and analyzed. An index (T4) was calculated and presumed to indicate the level of thyroxin. Lambs exposed to 90 dB showed a significant decrease in this T4 index, indicating that sound was a stressor; decreased thyroid activity is one indicator of stress.
Ames (1978) also examined the effect of sound stress on meat color of sheep. Forty-two lambs were subjected to various sound types and intensities. Color was examined 48 hours after slaughter by visual scores and reflectance spectrophotometry. White noise caused more blue and less red reflectance. Music at 100 dB resulted in brighter visual color. Color change was apparent in the meat of lambs exposed to IMS and white noise, indicating these sound types were more stressful.
As stated by Rylander et al. (1974) and Stephens (1980), sheep are keenly aware of novel stimuli, such as noise or sudden movements. Sonic booms are considered stressors on sheep because they induce a marked startle response that results in physiological changes, however brief (Espmark et al. 1974). Deviations from normal resting levels of various plasma hormones and other elements were detectable in sheep exposed to sudden stimuli, such as noise (Stephens 1980).
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Seventy-nine ewes were evaluated for the effect of sound type (at 100 dB), continuous versus intermittent exposure, and time of exposure (days 12-14 vs. days 14-17) on reproduction (Ames 1978). Exposure to 4,000-Hz pure tone on days 14-17 proestrus appeared to increase the number of corpora lutea produced in the ovary. Ames (1978) presumed that hypothalmic integration of sound stimuli affected the gonadotropin releasing factor, which altered ovarian function. Sound exposed ewes had significantly more lambs born than control ewes. At least over a short-term experiment, white noise or pure tone at 100 dB appeared to have no detrimental effect on reproduction. Several reviewers of noise research on animals also stated that data presently available indicate no impaired reproduction in sheep due to exposure to sonic booms (Ewbank 1977; Cottereau 1978).
Wild ungulates appear to be much more sensitive to noise disturbances than domestic livestock. Behavioral reactions appear to be related to the past history of disturbance (human and aircraft) on the population. Buffalo (Bison bison) on the Wichita Mountains National Wildlife Refuge near Fort Sill Oklahoma, "appeared oblivious" to F-105 overflights (Frazier 1972). The range has been operational since 1957 and is used to fire a variety of weapons, including Honest John missiles. The maximum noise level measured at these sites was below 90 dBA.
The degree of reaction of Arctic ungulates to noise disturbance due to aircraft appears to vary with group size, sex, season, activity engaged in prior to disturbance, previous exposure to noise source, and distance from noise source (Ruth 1976). Reindeer (Rangifer tarandus) kept in an enclosure were exposed to 36 sonic booms (varying from 35 Pa-702 Pa) for 3 days (Espmark 1972). The animals had experienced occasional exposure to sonic booms. No clear differences in reaction were seen between low and high boom strengths. Moderate reactions were found irrespective of boom level. Common reactions were slight startle responses, raising of head, pricking the ears, and scenting the air. Panic reactions or extensive changes in behavior of individual animals were not observed. Reindeer appeared to be more sensitive to disturbances during gestation and the calving season; thus, sonic booms could potentially have some negative influences on reproduction.
Increased use of low-altitude aircraft in remote areas occupied by ungulate populations has focused attention on possible effects of aircraft disturbance on wildlife (Klein 1973). Such disturbance is most detrimental in treeless terrain where escape cover is lacking. 0bservations of flight distances and other behavior of caribou (Rangifer tarandus) in Alaska were recorded in relation to altitude and angle of fixed-wing aircraft and helicopter approach, intensity and frequency of sound, and external factors such as weather and terrain. Running and panic occurred when the aircraft was at altitudes of 200ft or less, and such reactions decreased as flight altitudes increased. Above 500 ft, no panic response was observed. Groups of fewer than 10 animals responded less strongly to the aircraft than larger groups. Groups consisting primarily of cows, calves, and yearlings tended to show a stronger response to the aircraft than groups of bulls. Insufficient
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observations from the helicopter limited comparison of the two types of aircraft, but general observations indicated that animals showed a stronger reaction to the helicopter than to the fixed-wing aircraft. Incidental observations of other wildlife indicated that wolves were least disturbed by aircraft, moose (Alces alces) were less disturbed than caribou, and grizzly bear (Ursos arctos) were the most disturbed of all species observed.
The responses of barren-ground caribou (Rangifer arcticus) to fixed-wing aircraft and to helicopter were observed in the northern Yukon and Alaska (Calef et al. 1976). Escape or strong panic reactions were noted in 65%-75% of all groups observed from the fixed-wing aircraft at altitudes of up to 500 ft, but in only 10%-25% of the caribou observed from the helicopter. Caribou at river crossings reacted more to aircraft than traveling or feeding animals, and resting animals reacted least. Size of group, terrain, or vegetation type did not appear to affect the caribou's response to aircraft. Reactions during the calving season were stronger than during spring and fall migrations. Calef et al. (1976) recommended that aircraft fly at a minimum altitude of 500 ft during summer and fall migrations, and 1,000 ft at other times. Following the herd with a helicopter elicited extreme panic reactions, potentially dangerous to individuals in the herd. Calef (1974) also demonstrated that unfamiliar noise stimuli increased the incidence of miscarriages and lowered the birth rates of caribou.
0n a mesa in New Mexico, reactions of pronghorns (Antilocarpa americana)to helicopters were assessed by aerial photography (Luz and Smith 1976). At an altitude of 400 ft and a slant range from the herd of 3,000 ft, no reactions to the aircraft were observed. Mild reactions (muscle tensing and interruption of grazing) were observed as the craft moved toward the herd at a descent rate of 200 ft/min and a forward air speed of 40-50 knots. Strong reactions (running) began when the craft was at 150-ft altitude and a slant range of 500 ft. Calculated noise levels of no reaction and strong reaction were approximately 60 and 77 dBA, respectively.
Little is known of the long-term effects of noise on the physiology of wild ungulates. However, behavioral changes in wildlife resulting from exposure to sudden or loud noise, such as sustained running or avoidance behavior, cause increased expenditures of energy, which reduces the rate of survival and reproduction. This is particularly harmful during periods of stress, such as late winter. Klein (1973) stated that when aircraft fly at certain altitudes, caribou will run. For a 90-kg animal, the calculated energy expenditure due to aircraft harassment was 64 kilocalories per minute when running and 20 kilocalories per minute when walking. This compares closely to energy expenditure values obtained for other large ungulates when using Gold's (1973) "step rule" that energy cost of locomotion is approximately 3 x 0.0001 calories per gram per step. Under good conditions, increased energy expenditures can be compensated for by increasing food intake. Under adverse conditions, however, such as winter or drought, when increased forage intake is not possible, body reserves are drawn on, resulting in deterioration in the condition of the animals.
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Host of the research on physiological effects of noise on animals has been conducted with laboratory rodents. The guinea pig has been the laboratory animal most used for studying the mechanics of hearing damage to the ear. Beagley (1965) exposed guinea pigs to 128 dB SPL at 500 Hz for 20 minutes. This intense sound produced irreversible damage to the external hair cells and supporting cells of the third turn of the cochlea. There was no evidence of damage to the nerve tissue. Poche et al. (1968), Pye (1971, 1973), and Bobbin and Gondra (1975) confirmed the occurrence of localized damage and demonstrated that the severity of the damage was dependent on the duration of the exposure as well as sound intensity, and that the location of damage was more variable and widespread at low frequencies than at high frequencies. Conti and Borgs (1964) demonstrated a reduction in cytochrome oxidase activity in the cochlea of guinea pigs exposed to100 dB sound for 3 hours. Hajeau-Chargois et al. (1970) exposed guinea pigs to simulated sonic booms at a rate of one per second. The intensity of each boom was about 130 dB, with no reference level stated. Microscopic examination of the cochleas revealed damage to approximately 10% of the hair cells in the first turn of the cochlea. Covell (1953) reported marked histological changes in the organ of Corti of guinea pigs following exposure to intense sound of 50-100 kHz.
Anthony and Ackerman (1957) studied the stress effects of noise on bodily functions other than hearing in laboratory rodents. Physiological, biochemical, and behavioral effects of intense noise at low and high frequencies were examined using: (1) flame spectrophotometric analysis of serum electrolytes; (2) serum ascorbic acid and blood sugar changes; (3) changes in adrenal and. plasma cholesterol; (4) behavioral changes in noise-exposed rats, mice, and guinea pigs; and (5) relationship of seizure-susceptibility to noise stimulation. A corona speaker was designed and constructed for use in acoustic studies. Short daily exposures to intense noise of about 132- to 140-dB pressure levels induced physiological stress in guinea pigs, mice, and rats by increasing adrenocortical activity (manifested in "anxiety-like" behavior) under stimulation at low frequencies (150-4,800 Hz), and increasing audiogenic seizures at high frequencies (2-40 kHz). Animals appeared to adapt somewhat to noise stress; however, the fact that noise elicits a defense response makes it reasonable to assume that high levels of acoustic noise will overtax the homeostatic adaptive mechanisms.
Auditory damage has also been found in mice exposed to simulated sonic booms (Reinis 1976). Four groups of mice were subjected to a single sonic boom with a 5-msec rise time and duration of 100 msec. Peak overpressure was varied, with values of 1.3, 3.0, 4.0, and 10.0 psf. Mice were sacrificed 72 hours after exposure to the single sonic boom. Another group of mice was exposed to one to five sonic booms at a rate of one every 10 seconds. Although blood clots were never found in inner ears of control mice, they were found regularly in mice exposed to sonic booms of varying rise times and intensities. The blood clots were always found in the scala tympani at the basal turn of the cochlea. Only the superboom (10.0 psf) caused bleeding in more than 60% of the inner ears. The proportion of mice ears experiencing bleeding increased with more rapid rise time and a greater number of booms. Even a single boom having a short rise time of 0.1 msec and a peak overpressure of 3.3 psf caused
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inner ear bleeding. The effects of a short series of sonic booms were cumulative; two or more booms at 10-second intervals caused bleeding, whereas one did not. As few as five successive booms at a rate of only one every 24 hours produced a cumulative effect. The traces of bleeding usually disappeared within 8 weeks after exposure.
Anthony and Ackerman (1955) studied the effects of noise on blood eosinophil levels and adrenals of mice. One group of mice was exposed to intermittent sound of approximately l10 dB (unspecified reference). A timer switch turned the sound on for 100 minutes and off for 100 minutes alternately throughout the 4-week study. A second group of mice was exposed to a single morning sound exposure of 110 dB for 15 or 45 minutes daily for 1 to 3 months. Anthony and Ackerman (1955) found a slight decrease in circulating eosinophils approximately 3 hours after initiation of the sound stimulus. They also found indications of adrenal activation based on an increase in adrenal weight and by measurement of cellular changes in the adrenal cortex. However, the above stated changes were generally slight and transient. The results indicated that the noise level used was not sufficiently stressful to result in deleterious changes in the adrenals or other organs of the mice.
Busnel and Holin (1978) studied the effect of noise alone and noise plus two other stressors (vibration and crowding) on reproduction of mice. Direct effects of noise and indirect effects of stress reactions of the females were examined. Noise exposure consisted of 1-hr recorded subway noise (approximately 105 dB SPL) played four times daily. No significant differences were found in mothers' weights, number of young born, number of young surviving weaning, or sex ratios of young of the noise-exposed groups compared to the control group. However, noise-exposed mice experienced a longer time-interval between litters and lower weight gain of young. The incidence of miscarriage, resorption, and malformations increased in the stressed groups. Noise alone had less of an effect than when in combinations with the other two stressors.
Teratogenic potential of mice exposed to high intensity continuous noise, high intensity random noise, and high frequency noise was studied in a series of experiments (Nawrot et al, 1980). Groups of mice were exposed to noise during days 1-6 of gestation or days 6-15 (postimplantation). Noise consisted of continuous, extremely high-intensity jet engine noise at levels around 127 dB, random onset noise (i,e., alarm bells, warning devices, jet engine) at 103-110 dB, or high-frequency noise at 113 dB. A significantly decreased pregnancy rate was noted in all groups exposed to noise compared to control groups, except the group exposed to the high-frequency sound from days 6-15 gestation. Significant embryotoxic or lethal effects (decrease in the number of implantation sites per litter) occurred in mice exposed to the extremely high-intensity jet noise from days 1-6 gestation. Significant fetolethal effects occurred in mice exposed to the high-frequency noise from days 6-15 gestation. The fetolethal effects may have resulted from decreased uterine blood flow (possibly caused by catecholamines), resulting in diminished oxygen and nutrient supply to the fetus and retarded removal of waste products. Overall, teratogenic effects did not increase in the noise-exposed mice (all groups combined) compared to the control mice. Ishii and Yokobori (1960) reported teratogenic effects in offspring of female mice exposed to noise at sound pressure levels equivalent to 106 dB.
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Hoffman and Searle (1968) demonstrated that a weak sound signal could inhibit the intensity of the startle reaction in rats in response to an intense sound. Hoffman and Searle (1968) believed that weak signals could activate the neural mechanisms responsible for the startle reaction. They also found that after 675 stimulus exposures the rats had not habituated to the sound.
Holler (1978) and Borg (1979, 1981) studied long-term noise exposure in rats. The goal of these studies was to measure several body functions during the lifetime of the animals and compare their responses under three different noise conditions: (1) no noise except that generated by the animal's own movements, (2) moderate noise level of 85 dB SPL for 10 hours per day, and (3) relatively high noise level of 105 dB SBL for 10 hours per day. Both normotensive rats and spontaneous hypertensive strains of rats were tested. Results showed that the noise exposure levels used in this study did not affect blood pressure in either the normal or hypertensive rats. After 12-15 months of sound exposure, all animals were tested for hearing thresholds. The control animals and the animals exposed to 85 dB SPL did not differ with respect to threshold. The animals exposed to 105 dB SPL suffered significant hearing loss. The normotensive rats had a 30- to 40-dB loss compared to the control rats. The hypertensive rats had a profound hearing loss of at least 60 dB. These rats also showed a corresponding massive damage to the inner ear structures. The results suggested that noise did not cause hypertension, but hypertensive animals were more susceptible to noise-induced hearing loss. Rats housed in an environment where they were exposed to 85 or 105 dB SPL sound for 10 hours a day, for most of their lives, did not show any significant changes in blood pressure, body weight, water consumption, life span, or diseases.
Borg (1978a) studied the vascular response in rats as a function of the duration of a broad-band noise signal of 80 dB SPL. Sound stimuli were presented through a loudspeaker 10 cm in front of the rat and consisted of bursts of varying duration. The rise time of each burst was 1 msec. Sound bursts were presented at 15-minute intervals, with each session lasting between 8 and 12 hours. Noise bursts of durations less than 0.1 second were relatively inefficient for production of vasoconstrictions, and the vasoconstriction habituated slowly when the animal was exposed to continuous 80-dB noise.
Borg (1978b) also studied the sensitivity of vasoconstriction to rate of change of the sound level, using 1.0-sec or 4.0-sec stimulus (same noise signal as the previous study) and rise times of 1, 10, 100, or 1,000 msec. Each session lasted 4 to 12 hours, with the sound presented at 15-min intervals. A 4-sec sound burst produced a smaller vasoconstriction when the rise time was long than when it was short. However, sound bursts with faster rise times were equally efficient. Noise bursts with 1-sec and 4-sec duration gave almost identical vasoconstrictions as long as they had equal rise times, indicating that the vasoconstriction was more sensitive to rapid changes in sound level than slow changes.
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The offset of a continuous noise may elicit a vasoconstriction, but in most cases the vasoconstriction is caused by the onset of noise after the end of a pause (Borg 1978c). A pause as short as 10 msec produced vasoconstrictions the same length as pauses of many seconds' duration. Only for pauses shorter than 10 msec did vasoconstrictions decline . Vasoconstriction reflex was differentially sensitive to onset and offset of noise; onset was a more efficient stimulus. No clear evidence for habituation was apparent. Habituation seemed to depend on the individual animal; some rats showed no response to noise pause, others showed a consistent habituation. Buckley and Smookler (1970) provided evidence that extremely intermittent sounds presented over a few months leads to a rise in blood pressure. Either sound alone or sound in conjunction with other sensory stimuli produced hypertension.
Ogle and Lockett (1966) examined the effects on rats of recorded thunderclaps of 3- to 4-sec duration, frequency range of 50 to 200 Hz at 98 to 100 dB SPL, presented for 2 minutes out of every 15 minutes for 45 minutes. This was compared with effects from a pure tone of 150 Hz at 100 dB presented in the same sequence of time. Urine was collected for analysis of sodium and potassium. Responses were compared among animals that were intact, that had denervated kidneys, and that had neurohypophyseal lesions. Thunderclaps increased the urinary excretion of sodium and potassium by intact rats but not by neurohypophysectomized rats. Ogle and Lockett (1966) concluded that the thunderclaps produced emotional responses, and the pure tone did not. Thunderclaps affected the hypothalamus, resulting in excretion of oxytocin and vasopressin, which produced increases in sodium and potassium excretion with no increase in urine flow.
Sackler etal. (1959) studied the effects of auditory stress on body weight and various body organ changes. One group of rats was subjected individually to 1 minute of intense stimulus, while the control rats spent a corresponding minute in quiet. The stimulus was an electric buzzer with a mean intensity of 110 dB (unspecified reference). The rats received 11 consecutive daily treatments over a 2-week period. Another group of rats was subjected to 15 5-min treatments extending over a 3-week period. Animals exposed to 1-min treatments experienced significant adrenal weight loss and slight loss in body weight, thymus, spleen, pituitary, ovary, and uterine weights: they had a slight gain in thyroid weight. Animals receiving repeated 5-min exposures showed a significant increase in adrenal weights and a significant decrease in liver weights. The stimulus also produced a lowered rate of body weight gains. Similar to the 1-min treatment, weight gain was noted in the thyroid, and weight loss was noted in the thymus, ovary, uterus, and sp