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DECIBEL LEVEL OF FIRECRACKERS AND ITS POSSIBLE IMPACT
ON THE HEARING OF MARAUDING ELEPHANTS IN SRI LANKA
V. Sivakumar
1
, ** J.A.P. Bodhika
2
, Ruchira Jayatillaka
3
, Chandrawansa Pathiraja
4
,
S.K. Pathiratne
5
, S.R.B. Dissanayake
5
, S. Wijeyamohan
6 ,77777 77
and Charles Santiapillai
6
1
Department of Physics, University of Peradeniya, Sri Lanka
2
Department of Physics, University of Ruhuna, Matara, Sri Lanka
3
National Aquatic Resources Research & Development Agency, Sri Lanka
4
The then Director-General, Dept. of Wildlife Conservation, Battaramulla, Sri Lanka,
5
Department of Wildlife Conservation, 811/A Jayanthipura Road, Battaramulla, Sri Lanka
6
Ringling Bros, Center for the Study of Asian Elephant, Rajarata University,
Mihintale, Sri Lanka
7
The William H. Darr School of Agriculture, Missouri State University, Springfield,
Missouri, USA
Abstract: Today the human-elephant conflict has come to its climax due to rapid
urbanization and increase in population of humans as well as elephants in Sri Lanka. As a
result damages to humans, crops and properties of the adjacent forest communities by the
wild elephants and retaliatory killing of elephants by humans have received wide coverage in
the press and media. The Department of Wildlife Conservation (DWC), in an effort to
mitigate the escalating conflict, has been providing farmers with powerful firecrackers on a
regular basis. It is alleged that the constant use of extremely loud firecrackers in agricultural
areas and home gardens by farmers may have impaired the sense of hearing among some
elephants thereby making them unresponsive to such deterrents. This research study was
carried out to assess the impact of firecrackers on the hearing of elephants in Sri Lanka. The
results from our preliminary study show that the decibel levels of the two types of
firecrackers used by villagers ranged between 137 and 140 dB at a distance of 30 m.
Spectrograms verify that the frequency generated in high sound pressure levels distributed
from infra sound region to around 400 Hz. But in some cases the upper limit of the frequency
reached even 1000 Hz with the sound pressure level around 125 dB which is the more
sensitive range for elephants. Most of the time villagers throw crackers on to the body of the
elephant itself, in which case, the high decibel level of the firecrackers could seriously impair
its hearing.
Keywords: Elephant, Human-Elephant Conflict, Firecrackers, Spectrogram, Deafness, dB
levels,
Introduction
One of the commonest methods used to chase marauding elephants off agricultural
fields in Sri Lanka is by throwing firecrackers at them. Farmers faced with chronic crop
raiding elephants try a variety of methods to stop their depredation of which the use of
International Journal of Science, Environment ISSN 2278-3687 (O)
and Technology, Vol. 2, No 4, 2013, 593 – 600
7,7
Received June 26, 2013 * Published August 2, 2013 * www.ijset.net
Email: jbodhika@phy.ruh.ac.lk (*Corresponding Author)
*
594 V. Sivakumar, J.A.P. Bodhika, Ruchira Jayatillaka and others
firecrackers has become routine. The Department of Wildlife Conservation (DWC), in an
effort to mitigate the escalating conflict between man and elephant has been providing
farmers with powerful firecrackers on a regular basis. In addition, villagers too buy
firecrackers on their own to throw at elephants as a last ditch effort to keep them at bay.
Elephants being extremely intelligent, soon come to differentiate between the weak and the
powerful firecrackers. They seem to be wary of loud explosions, especially if they happened
to go off very close to where they are. It is alleged that the constant use of extremely loud
firecrackers in agricultural areas and home gardens by farmers may have impaired the sense
of hearing among some elephants. Such “deaf” elephants will no longer be able to respond to
shouts or noise made by farmers and hence may stray deeper into cultivated areas and linger
longer thereby facing the danger of being killed by farmers in sheer desperation. The present
study was carried out to understand the problem given that to date no one has attempted to
assess the impact of firecrackers on the hearing of elephants in Sri Lanka.
Humans and animals can hear a wide range of sound frequencies, pitches or tones. If the
sense of hearing is impaired, both man and elephant cannot fare well in their respective
environments. Elephants typically do not have as far reaching eyesight as humans do, but
their sense of smell is unparalleled given that they are able to track the location of family
members by even sniffing their urine (McKenna, 2007; Bates et al., 2008). In addition, they
are capable of hearing sound well below human hearing limitation, from 5 Hz to 12,000 Hz.
A normal human being can hear sound frequencies between 20 Hz and 20,000 Hz. Elephants
can hear very low frequency sound (best sensitivity at 1,000 Hz) extending into the
infrasound region (Heffner & Heffner, 1980; Reuter & Nummela, 1998), but their threshold
for high-pitched sound is somewhat lower than that of human beings.
Sound can reach the mammalian inner ear via two routes: through (a) the air (air-conducted)
and (b) the bones (bone-conducted) effective in aquatic and fossorial mammals (Reuter &
Nummela, 1998). The intensity of sound is measured in decibels (dB). Decibel is a
logarithmic unit used to describe the ratios of sound pressures; measured and the reference.
By definition the sound pressure level in decibel scale is given by the following equation:-
Where the P is the measured pressure and the P
0
is the reference pressure, 2x10
-5
N m
-2
. It is
clear from the above expression that the sound pressure level variation with the sound
Decibel Level of Firecrackers and Its Possible Impact on ………. 595
pressure is not linear. That means when the sound pressure doubles the sound intensity level
does not double, instead it increases by just 6 decibels.
The human ear is an extremely sensitive organ that can hear from the smallest audible sound
such as a whisper (30 dB) to that of a gunshot (140 dB). In the case of humans, constant
exposure to sound of 90-95 dB may lead to a loss of hearing, while exposure to sound at 125
dB is extremely painful; and at 140 dB even short exposure would lead to permanent ear
damage. Therefore, given that the elephant’s upper limit of hearing is slightly less than that of
ours, we expect the use of loud firecrackers at close range may seriously impair the
elephant’s sense of hearing. Distance also affects the intensity of sound – if an animal is far
away, the power is greatly diminished.
Methodology
Three types of firecrackers, large, small and one referred to as “signal” issued by the
Department of Wildlife Conservation (DWC) were used in the experiment to determine their
decibel levels at various distances from the target. The large and small crackers are designed
to produce loud sound whereas the “signal” firecracker is designed to jump up and down
once it explodes. The experiment was conducted at an open field at University of Ruhuna (Sri
Lanka) and in a home garden at a southern border village in Hambantota (Sri Lanka) in 2011,
using microphones, preamplifier, conditioning amplifier and signal acquisition device. Three
Bruel & Kjaer type 4198 pre-polarized, free-field ½” microphones, stable under a variety of
conditions were used. Sensitivity of the microphones was 50 mV/Pa. The frequency response
of ±1 dB ranged from 10 Hz to 8 kHz and of ±2 dB from 6.3 Hz to 16 kHz. The preamplifier
2669C had wide frequency and dynamic ranges with low noise and operated over a wide
range of temperatures, humidity and other environmental conditions. 2690 Nexus
conditioning amplifier was used with NI 4472, 24 bits resolution, high-performance and high
accuracy dynamic signal acquisition device. Experimental setup was calibrated using B&K
sound calibrator type 4231. Wind screens were used to reduce the ambient wind noise. The
sampling rate was set to 100,000 per second. The data was analyzed using MATLAB
software.
Results
Fig. 1 illustrates the variations in sound level with distance as measured in the case of the
three types of firecrackers issued by the DWC on an open area.
596 V. Sivakumar, J.A.P. Bodhika, Ruchira Jayatillaka and others
Fig. 1. Sound pressure level variation with distance measured in the case of the large, small
and “signal” firecrackers on an open field at University of Ruhuna, Sri Lanka.
Fig. 1 shows how the sound pressure level (calculated using 2x10
-5
N m
-2
as reference) varies
with distance from the point of explosion, as measured on an open field using the three
different types of firecrackers issued by the DWC. Due to high sound pressure produced by
the crackers and the inherent limitations of the instrument used, the closest distance at which
an accurate measurement could be made was 30 m from the point of explosion.
Even at 30 m distance from the point of explosion, the sound pressure levels recorded for all
large, small and “signal” crackers ranged between 137 to 140 dB. The uncertainty of the
microphone reading in this frequency range was ±1 dB. Both “signal” type and the small
cracker produced the same sound level but the large type has about 3 dB more than the other
two at 30 m distance, and such a difference increased with distance away from the explosion
point.
Three microphones were placed at 10 m intervals. There was variation in the quality of the
firecrackers. The sound intensity produced by the firecrackers produced different intensity of
sound at the same distance. As a result, the last three sound intensities from the “signal” type
were higher than that from the small firecracker (Fig. 1). Furthermore, from Fig. 1 it appears
that the variation of attenuation of sound intensity is a function of the firecracker. Sound
30 40 50 60 70 80 90
124
126
128
130
132
134
136
138
140
142
Small
Signal
Large
Sound Pressure Level vs Distance
Sound pressure Level (dB)
Distance (m)
Decibel Level of Firecrackers and Its Possible Impact on ………. 597
levels produced by small firecracker attenuate more rapidly than those produced by the larger
one.
Fig. 2. Sound pressure level variation with distance measured in the case of large and small
firecrackers in a southern border village, near Hambantota, Sri Lanka.
As can be seen from Fig. 2, the closest distance to make an accurate measurement of sound
pressure was at 30 m from the point of explosion. Owing to many restrictions, only three
measurements were taken at 30, 35 and 40 m from the point of explosion, using two types of
firecrackers, large and small. At 30 m distance, the sound pressure level of both firecrackers
was between the 137 and 140 dB range, similar to that recorded on the open ground.
30 32 34 36 38 40
128
130
132
134
136
138
140
Sound Pressure Level vs Distance
Small
Large
Distance (m)
Sound Pressure Level (dB)
30 32 34 36 38 40
128
130
132
134
136
138
140
Comparison of Sound Pressure Level vs Distance
Sound Pressure Level (dB)
Distance (m)
Small in vegetation
Large in vegetation
Small in open space
Large in open space
598 V. Sivakumar, J.A.P. Bodhika, Ruchira Jayatillaka and others
Fig. 3. Comparison of sound pressure level variation with distance measured for large and
small type crackers in both open and border village areas
Fig. 3 shows the comparison of the variation in the sound intensity level within 30 – 40 m
from the point of explosion measured on the open ground and in the home garden in the
border village. The attenuation of sound intensity level in the village is much higher than that
on the open ground. As seen in Fig. 3, within 10 m range on the open ground the sound
pressure level attenuated by 0.3 dB for every one meter distance while this decay in the
village area was in the range of 0.8 - 1.0 dB per meter. This shows that the propagation of
sound wave is influenced by both geometrical spreading and access attenuation. Though the
geometrical spreading is similar in both cases, access attenuation is high in village area.
Fig. 4 shows the spectrograms of both large and small firecrackers measured at 30 m from the
blasting point. Frequency distribution during the blast is almost the same in both cases. The
frequency generated in high sound pressure levels distributed from infra sound region to
around 400 Hz. But for large firecrackers, the upper limit of the frequency even increases to
1000 Hz with the sound pressure level around 125 dB. It should be noted that the elephants
are more sensitive to 1000 Hz frequency (Heffner & Heffner, 1980; Reuter & Nummela,
1998). Spectrograms also verify the sound pressure levels generated by firecrackers are
increased instantly up to 140 dB and the level retain few milliseconds with the background
noise.
Fig. 4. Spectrograms of large and small crackers. Horizontal axis reads the time in seconds,
and vertical axis reads frequency in Hz. The color of spectrogram represents the sound
pressure level in dB according to the given scale in right side of the graph.
Decibel Level of Firecrackers and Its Possible Impact on ………. 599
Discussion
Of all the vertebrates, it is only the mammals that can hear high-frequency sounds. However
mammals differ in their ability to hear high-frequency sounds. While a healthy human being
can hear a frequency range from 20-20,000 Hz, an elephant’s hearing range lies between 5-
12,000 Hz. Elephants seem to hear well low frequency sounds. High frequency hearing has
been shown to be correlated not with body weight but with the functional distance (i.e. the
interaural distance divided by the speed of sound) between the two ears (Bates et al., 2008).
This is the reason why small mammals such as shrews are better able to hear high frequency
sounds compared to such large mammals as elephants. Loudness is subjective and varies
from people to people with age. Similarly, elephants too could differ in their perception of
sound, with young animals being more sensitive than older ones. Loud explosions that peak
for a few milliseconds at levels greater than 130-140 dB are known to cause loss of hearing in
man. The human audiogram and that of the elephant are essentially similar in shape.
The results from our preliminary study show that the decibel levels of the two types of
firecrackers used by villagers range between 137 and 140 dB at a distance of 30 m. Human
hearing will certainly be impaired if exposed constantly to such high sound levels. Given that
the audiograms for both man and elephant are very similar, we suspect that even elephants
subject to such high intensity sound constantly could be affected. But elephants can also use
their pillar-like bones in their legs to conduct the surface waves to the inner ear (Reuter &
Nummela, 1998). But the fact that some individual bull elephants seem to be unaffected by
loud noise and linger in human settlements and raid crops indicates that they may be partially
deaf or very old and thus insensitive to the impact of fire crackers. Hearing range can
decrease after long-term or constant exposure to loud noise. The Department of Wildlife
Conservation (DWC) provides extremely powerful firecrackers to the villagers for use
against marauding elephants. However, given that the demand for such firecrackers exceeds
the supply, the DWC invariably provides just 3 firecrackers per family per month in areas of
high human-elephant conflict. As a result, the families reserve these firecrackers as a last
ditch defense against marauding elephants, and throw them only when an animal is close
enough, often on the body itself, in which case, the high decibel level of the firecrackers
could seriously damage the hearing in elephants. Thus conservation education programs need
to be carried out in villages to offer alternative solutions to mitigate the conflict between man
and elephant.
600 V. Sivakumar, J.A.P. Bodhika, Ruchira Jayatillaka and others
Acknowledgement
We would like to acknowledge with thanks the receipt of the research grant
(#RU/DVC/Pro.61, TURIS project) from the Department of Physics, University of Ruhuna,
and the Atmospheric Physics and Lightning Research Group at the University of Colombo,
Sri Lanka. In addition, we would like to thank the Department of Wildlife Conservation for
providing us with all the facilities and assistance in the field to carry out the research. We
would also like to express our thanks to Mr. Kenneth Feld, Chairman & CEO, Feld
Entertainment, Inc. USA for his generous financial assistance.
References
[1] McKenna, P. 2007. Elephants use mental maps to track family members - New Scientist.
Available at: http://www.newscientist.com/article/dn12998.html.
[2] Bates, L.A., Sayialel, K.N., Njiraini, N.W., Poole, J.H., Moss, C.J., Cyrne, R.W. (2008)
African elephants have expectations about the locations of out-of-sight family members.
Journal of Animal Behaviour. 4: 34-36.
[3] Heffner, R. & Heffner, H. (1980) Hearing in the elephant. Science, 208: 518-520.
[4] Reuter, T. & Nummela, S. (1998) Elephant hearing. J. Acoust. Soc. Am., 104: 1122-123.