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The behavioral audiogram of whitetail deer (Odocoileus virginianus)

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The behavioral audiograms of two female white-tailed deer (Odocoileus virginianus) were determined using a conditioned-suppression avoidance procedure. At a level of 60 dB sound pressure level, their hearing range extends from 115 Hz to 54 kHz with a best sensitivity of -3 dB at 8 kHz; increasing the intensity of the sound extends their hearing range from 32 Hz (at 96.5 dB) to 64 kHz (at 93 dB). Compared with humans, white-tailed deer have better high-frequency but poorer low-frequency hearing. (C) 2010 Acoustical Society of America
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The behavioral audiogram of whitetail deer
(Odocoileus virginianus)
Henry Heffner, Jr. and Henry E. Heffnera)
Whitetail Deer Research LLC, P.O. Box 412, Swanton, Ohio 43558
hheff@adelphia.net, heff270@yahoo.com
Abstract: The behavioral audiograms of two female white-tailed deer
(Odocoileus virginianus) were determined using a conditioned-suppression
avoidance procedure. At a level of 60 dB sound pressure level, their hearing
range extends from 115 Hz to 54 kHz with a best sensitivity of −3 dB at
8 kHz; increasing the intensity of the sound extends their hearing range from
32 Hz (at 96.5 dB) to 64 kHz (at 93 dB). Compared with humans, white-tailed
deer have better high-frequency but poorer low-frequency hearing.
© 2010 Acoustical Society of America
PACS numbers: 43.80.Lb, 43.66.Gf, 43.66.Cb [CM]
Date Received: November 10, 2009 Date Accepted: December 10, 2009
1. Introduction
White-tailed deer have perhaps the largest economic impact of any wild animal in North
America. On the one hand, billions of dollars are spent each year on equipment and travel
related to deer hunting (e.g., Conover, 1997). On the other hand, deer spread Lyme disease,
causing millions of dollars of damage to both the agriculture and timber industries, and over a
billion dollars of damage to vehicles that collide with them each year (Conover, 1997;Schwabe
and Schuhmann, 2002). Indeed, more than 100 people are killed each year in deer-vehicle col-
lisions, with many more seriously injured, making deer the most deadly wild animals in North
America (Bailey, 2001). As a result, there is much interest in the behavior of white-tailed deer,
particularly in their sensory abilities (e.g., Gerlach et al., 1994).
Because deer are naturally afraid of humans and do not readily tolerate our presence, it
is difficult to conduct behavioral tests on them. As a result, the only measure of their hearing
currently available is their auditory brainstem response (D’Angelo et al., 2007). This measure-
ment indicates that the hearing range of deer extends from 250 Hz to 30 kHz, with a best sen-
sitivity of only 42 dB at 4 and 8 kHz. However, the auditory brainstem response does not give an
accurate measure of an animal’s absolute sensitivity nor does it necessarily indicate the relative sen-
sitivity of an animal to different frequencies (Heffner and Heffner, 2003). Such information can only
be obtained from a behavioral audiogram.
We present here the absolute pure-tone thresholds obtained for two domestically raised
whitetail deer using standard animal psychophysical procedures. These results will be of inter-
est to those who wish to attract, repel, or conceal their presence from deer.
2. Method
The animals used in this experiment were two whitetail does (Odocoileus virginianus)
12 years of age that had been born and raised domestically. The animals were weighed daily dur-
ing testing to help monitor their health.
The deer were tested using a conditioned-suppression avoidance procedure in which a
thirsty animal was trained to maintain mouth contact with a small stainless steel water bowl in
order to receive a steady trickle of water. The bowl, which was mounted on a post 0.5 m above
the floor, was carefully positioned so that the animals made little or no drinking noise. Pure tones
were then presented at random intervals followed by a mild electric shock delivered between the
aAuthor to whom correspondence should be addressed.
H. Heffner, Jr. and H. E. Heffner: JASA Express Letters DOI: 10.1121/1.3284546Published Online 11 February 2010
J. Acoust. Soc. Am. 127 3, March 2010 © 2010 Acoustical Society of America EL111
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bowl and the floor. An animal avoided the shock by breaking contact with the bowl whenever it heard
a tone, thereby also indicating that it had detected the tone. Thus, the task resembles the natural
situation in which an animal at a water hole pauses when it senses danger. That the shock level used
was “mild” was indicated by the fact that the deer never developed a fear of the water bowl and
returned to it as soon as the sound was turned off (for details of this procedure, see Heffner and
Heffner, 1995).
Thresholds were determined by reducing the intensity of a tone in 5 dB steps until an
animal could no longer detect it above chance level. Threshold was defined as the intensity at which
an animal could detect a sound 50% of the time (corrected for false positives), which was usually
calculated by interpolation (Heffner and Heffner, 1995).
To produce the tones, sine waves were generated with an oscillator or a digital signal
generator, gated with a rise-fall gate set to at least 10 ms to eliminate onset and offset artifacts,
pulsed (400 ms on, 100 ms off), filtered (±1/ 3 octave settings), monitored with an oscilloscope,
amplified, and sent to a loudspeaker: either a subwoofer 32– 63 Hz, woofer 125 4 kHz, piezo-
electric tweeter 8–32 kHz, or leaf tweeter (45, 56, and 64 kHz). Most testing was conducted with
the speaker placed in front of the animal at a distance of 1 m. However, because the animals some-
times did not point their pinnae forward, a second speaker was placed off to one side or behind an
animal at a distance of 1.5 m or more with the exact location depending on the direction in which an
animal tended to point its pinna. The procedure for calibrating the sound has been described else-
where (Jackson et al., 1997) and the sound pressure level (SPL) used was referenced to 20 µN/m2.
Testing was conducted in a single-wall sound-proof chamber, the walls and ceiling of which were
lined with acoustic foam.
3. Results
The deer learned to enter the sound chamber, drink from the water bowl, and break contact with
the bowl whenever a suprathreshold stimulus was presented. Although the animals usually
pointed their pinnae straight ahead at the loudspeaker located in front of them, they sometimes
rotated their pinnae to the side or back as though they were checking for sounds coming from
those directions. When this occurred, the tone trials were delayed until their pinnae were again
directed toward the loudspeaker. However, for frequencies of 8 kHz and higher, a second loud-
speaker was placed in the location toward which they oriented their pinna.This procedure resulted in
stable thresholds that represent the animals’ optimal sensitivity.
The audiograms of the two deer, shown in Fig. 1, have the characteristic shape of
Fig. 1. Absolute thresholds of two white-tailed deer A and B. The solid line indicates the average thresholds of the
deer. The dashed line is a human audiogram obtained in comparable free-field conditions Jackson et al., 1999.The
horizontal dotted line indicates the 60 dB sound pressure level, which is the level commonly used when comparing
the hearing ranges of different species.
H. Heffner, Jr. and H. E. Heffner: JASA Express Letters DOI: 10.1121/1.3284546Published Online 11 February 2010
EL112 J. Acoust. Soc. Am. 127 3, March 2010 H. Heffner, Jr. and H. E. Heffner: Audiogram of whitetail deer
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mammalian audiograms. Beginning at the low frequencies, the deer were able to hear 32 Hz at
an average threshold of 96.5 dB with sensitivity improving as frequency was increased.The animals
showed a broad range of good sensitivity extending from 500 Hz to 32 kHz with a best threshold of
−3 dB at 8 kHz. Above 32 kHz, sensitivity decreased rapidly to an average threshold of 93 dB at
64 kHz. Overall, at an intensity of 60 dB SPL, the deer were able to hear from 115 Hz to 54 kHz.
4. Discussion
There are two points to note about this deer audiogram. First, because sounds were only pre-
sented when at least one, if not both, of an animal’s pinnae were pointed toward a loudspeaker,
they represent the animals’optimal sensitivity. As has been demonstrated in reindeer, the pinnae
of deer are directional for high frequencies and sensitivity may be reduced by 20 dB or more
when the pinnae are pointed away from the sound source (Flydal et al., 2001). Second, although we
only tested females, these results are expected to apply to male deer as well, as the auditory sensitiv-
ity of mammals has not been observed to differ between the sexes (Heffner and Heffner, 2003).
Because of the extensive interactions between humans and white-tailed deer, it is of
interest to compare their audiogram with that of humans. As can be seen in Fig. 1, the deer
audiogram is similar in shape to that of humans and, indeed, looks like the human audiogram
shifted approximately two octaves toward the higher frequencies. Some of the differences be-
tween the human and deer audiogram are well understood. In particular, the better high-
frequency hearing of deer is explained by the observation that mammals rely on high-frequency
cues to localize sound, high frequencies being particularly important for localization in the
vertical plane and for preventing front-back confusions (Heffner and Heffner, 2008). However,
because the directionality of high frequencies depends on the size of an animal’s head and
pinnae, the smaller the animal, the higher it must hear in order to use the high-frequency locus
cues. Thus, deer hear higher than humans because they are smaller. However, less is known
about the variation in mammalian low-frequency hearing and there is currently no explanation
for the difference in the low-frequency sensitivity of humans and deer (Heffner and Heffner,
2003). (The audiograms of other mammals are available at http://psychology.utoledo.edu/
showpage.asp?name=mammal_hearing for comparison with deer.)
Finally, the audiogram provided here can be used to obtain a preliminary estimate of
the audibility of a sound to deer. That is, sounds whose spectra fall within the bounds of the
audiogram will be audible to deer if they reach a deer’s ear at a sufficient sound pressure level.
Sounds that fall above or below the frequency range of deer will not be audible to them regard-
less of the intensity. However, care must be taken in using these data to estimate the relative
loudness of sound to deer.This is because the audiogram measures the sensitivity to pure tones,
whereas most sounds of interest are complex sounds containing multiple frequencies, and it has
been shown that the perceived loudness of such sounds is not easily estimated from measures of
pure-tone sensitivity (e.g., Hellman and Zwicker, 1987).
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Redistribution subject to ASA license or copyright; see http://acousticalsociety.org/content/terms. Download to IP: 178.18.19.222 On: Thu, 29 Oct 2015 10:51:56
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: Basic knowledge of white-tailed deer (Odocoileus virginianus) hearing can improve understanding of deer behavior and may assist in the development of effective deterrent strategies. Using auditory brainstem response testing, we determined that white-tailed deer hear within the range of frequencies we tested, between 0.25–30 kilohertz (kHz), with best sensitivity between 4–8 kHz. The upper limit of human hearing lies at about 20 kHz, whereas we demonstrated that white-tailed deer detected frequencies to at least 30 kHz. This difference suggests that research on the use of ultrasonic (frequencies >20 kHz) auditory deterrents is justified as a possible means of reducing deer—human conflicts.
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Loudness measured by the method of absolute magnitude estimation is compared to loudness calculated in accordance with ISO 532 B (International Organization for Standardization, Geneva, 1966). The measured and calculated loudness functions exhibit a similar pattern of loudness growth. Both measured and calculated loudness of a complex sound composed of a 1000-Hz tone and broadband noise is a nonmonotonic function of the overall SPL of the complex. The nonmonotonic loudness-growth pattern holds over a 30-dB range from 73.5 to 103.5. To facilitate understanding of the results, a single cycle of data is analyzed in detail. The analysis shows that loudness patterns produced in the auditory system by the tone-noise complex can account for the observed effects. Moreover, they show that the A-weighting and the loudness of the complex are negatively related. This inverse relation means that the A-weighted SPL is an inappropriate and misleading indicator of the loudness of sound combinations with heterogeneous spectral envelopes. Consequently, its suitability for noise control is diminished. A loudness meter that combines the spectral shapes of different sounds to produce an overall perceived magnitude offers greater promise.