winds coincide (Figure 9.6).
The area over which an estrous call being made by a female elephant can
be detected by a male governs the number of males reached by that call. Under
poor daytime conditions, this area may be less than 3 km2 (1.9 mile2); under the
best early evening or morning conditions, the area will be more than 300 km2
(118 mile2). In the first instance of less than 3 km2 (1.2 mile2), no males may be
found. In the second instance, a number of males will be able to hear the call.
Researchers have been unable to find any distinctive structure to the loud
estrous calls made by elephants. Payne (1998), however, found that females in
estrous called more frequently than at other times and that males may recognize
this pattern of calling rather than deciphering the content of the call. The mat-
ing pandemonium emitted by both the female in estrous and her family, as de-
scribed earlier in this chapter, would, however, represent a distinctive signal to
distant males. McComb et al. (2003) found that calls around 100 Hz contained
a complex pattern of formant frequencies spanning several harmonics that iden-
tified the caller. They concluded that the content of these calls was critical to
social recognition and identification of the caller. The playback experiments
were conducted between 07:00 and 13:00 h but were not registered against sun-
rise or details of the near-surface temperature and wind fields. Wind speeds
were reported to be low (7 mph) but no information was given on how and at
what height these winds were measured, nor whether gusts exceeded the 7 mph
threshold. McComb et al. concluded that content was as important as the range
of the caller and that social recognition was thus probably limited to less than
2.5 km (1.5 mile). These conclusions, while valid for the times and place that the
experiment was conducted, cannot be generalized over 24 h and are likely to be
substantially different at other times within the 24 h.
More importantly, however, is that if, as both Payne (1998) and Soltis (2010)
have suggested, females before or during estrous call at a characteristic rate
66 Elephant Sense and Sensibility
200
150
100
Height (m)
50
0
30
40
(a)
Temperature (°C)
0
–20
–40
ion (dB)at –60
–80
Attentu
–100
0
2
4
6
8
10
(b)
Range (km)
FIGURE 9.6 Idealized temperature structure for three times of day: (a) dotted line: midday, dashed line: transition between daytime heating and nighttime cooling, solid line: nocturnal inversion, and (b) the resulting range or distance for each temperature profile that one elephant can hear another elephant’s loud (117 dB) low-frequency (15 Hz) call with a threshold of hearing of 49 dB.
Based on Larom et al. (1997).
(i.e., make a digital call), these calls are independent of loss of content and can be
heard and interpreted at much greater ranges. Using a calling pattern that trans-
mits crucial information over the greatest distance, independent of call content,
may have found its origins in the dense forests in which elephants evolved.
TIMES AND FREQUENCY OF CALLING
It has been suggested above that elephants, particularly mature females, may
produce low-frequency calls on an almost continuous basis. Only Langbauer
and Payne (Langbauer et al., 1991) have attempted to record calls of elephants
on a continuous basis (Figure 9.7). They collared 14 female elephants in the Sengwa Reserve in Zimbabwe carrying sound recorders that would record only
the loudest low-frequency calls. Calls below a given sound-pressure level were
Communication Chapter | 9 67
200
180
160
140
120
calls
100
80
Number of
60
40
20
012
18
0
3
6
12
Hour of day (LST)
FIGURE 9.7 Number of loud, low-frequency calls made in each hour recorded from 14 collared adult elephants ( L. africana) in the Sengwa Reserve in Zimbabwe. The thin vertical lines delineate the daytime heating and nighttime cooling as in Figure 9.5. Langbauer and Payne (personal communication, 2000); Garstang et al. (2005).
not recorded. Thus, a full spectrum of calls is not available, yet the record of
loud, low-frequency calls is known.
These collared elephants show a clear maximum in calling in the early eve-
ning at a time when nocturnal cooling, inversion formation, and low wind speed
coincide. As the night progresses, calling rates decline starting once again in the
second hour after surface heating begins. Loud, low-frequency calling during
the day continues at an average rate per elephant of about eight calls per hour,
or one loud call every 8 min.
Garstang and his colleagues (2005) placed eight microphones around a remote
waterhole (Mushara) in the eastern end of the Etosha National Park in Namibia.
A continuous record of all the calls recorded was analyzed for 8 consecutive days
in September 1999 (Figure 9.8). This record differs in a significant way from that 200
100
Number of
recorded calls
0 12
18
0
6
12
Hour of day (LST)
FIGURE 9.8 The number of elephant low-frequency calls (<100 Hz) recorded over 8 consecutive days (13–20 September 1999) in each hour in eastern Etosha National Park. Thin vertical lines as
for Figure 9.7. Based on Garstang et al. (2005).
68 Elephant Sense and Sensibility
of the collared elephants. In that record, it is the number of loud, low-frequency
calls made by 14 individual elephants. In the Mushara record, it is the number of
calls heard or detected. Since calling activity is probably contagious, such that
elephants call more often when they hear more calls, the observed distribution
of calls at the Namibian site will be a product of the proximity of elephants to
the recording site (the waterhole). The number of elephants calling, the calling
behavior of these elephants, and the number of calls that can be detected by the
microphones are all a function of the prevailing atmospheric conditions. Under
optimum acoustic conditions (strong low-level inversion with no wind), the mi-
crophones at the waterhole may detect calls of animals in a surrounding area of
300 km2 (118 mile2). Under the worst acoustic conditions (strong surface heating
and surface winds), this area will have shrunk to a less than 3 km2 (1.2 mile2).
The distribution of calls recorded over the 24 h at Mushara is thus dramatic:
42% of the 1400 calls recorded occur in the 3 h following sunset (19, 20, 21 h,
local standard time) and 29% are recorded in the 2 h following sunrise (08, 09),
for a total of 71% of all of the calls recorded in 24 h. Both of these peaks in calls
recorded occur at times when atmospheric conditions are at or near optimum for
the transmission of low-frequency sound. Of the remaining 30% of all detected
calls, 25% occurred at night, leaving only 5% for the daytime hours. While
the observed distribution of calls recorded reflect the presence and absence of
elephants at a watering site, the calls are recorded most often when the call
travels the furthest.
These observations suggest that elephants also make more calls when they
hear more calls. The number of calls recorded by our microphones during times
of optimum atmospheric acoustic conditions suggest that the calling rate is in-
fluenced by the number of calls heard. Such a hypothesis would need careful
identification of both caller and receiver, perhaps to the extent that the precise
timing and location are known.
Payne (personal communication, 1995) was able to track the movements
of herds within communication ranges of each other. She noted, in particular,
that adjacent herds while approaching each other never cross paths. To do so
would be energetically costly. A given adult elephant consumes between 150
and 200 kg of vegetation in each 24 h. At the end of the dry season a herd of
elephants consisting of 10–20 adults plus young would largely denude the
area over which they are feeding of most of the edible vegetation. A second
herd coming into this area would find little to eat. Payne’s observations sug-
gest that the signals of each herd are used by the other to modify their feeding
pattern. It is quite possible, given earlier discussion (Chapter 5) of the ability
of elephants to recognize other elephants based entirely on call recognition,
that elephants in one herd are aware of the number and composition of an
adjacent herd.
Researchers in the field elect to work in daylight. Far fewer observations
are made at night yet it is clearly imperative that it is the cycles of the natural
biological and physical world that should be considered rather than entrenched
Communication Chapter | 9 69
human behavior. Increasingly, we are able to measure variables remotely and
continuously. Our defective field observing systems will progressively improve,
although the reluctance of the natural scientist to recognize the role of the physi-
cal world and document its behavior concurrent with that of the living world is
still in need of substantial improvement.
ABIOTIC SOUNDS
Elephants with their exceptional sense of hearing detect signals from the biotic
as well as the abiotic world. Both O’Connell-Rodwell et al. (2001, 2004) and
Hägstrum (2000) have reported that animals may detect and use seismic signals.
Garstang (2009) has suggested that in the wake of the Sumatran earthquake
on 26 December 2004, elephants in both Sri Lanka and Thailand, 1000 km
(620 mile) away, were able to detect the sound in the atmosphere generated by
the tsunami wave crashing on the shores of Sumatra.
Sound in the atmosphere travels slightly faster at sea level than the speed
of the tsunami (1200 km h−1 (750 mile h−1) vs. 700 km h−1 (440 mile h−1)). At
1000 km (620 mile) from Sumatra the sound wave would arrive a little less than
40 min before the tsunami struck. Anecdotal evidence indicates that elephants
in both Sri Lanka and Thailand responded 20–60 min prior to the arrival of
the tsunami. This 40 min advance notice of the sound wave falls within this
20–60 min time window. Elephants on the beach in Thailand had just returned
from giving tourists rides. They were chained to stakes driven into the ground
just off the beach. These elephants were reported to have screamed, broken the
restraining chains, pulled the stakes out of the ground, and run to high ground
all within the above time frame of 20–60 min.
Two other potential cues could have alerted these elephants on the beach
to the threat of a tsunami. Water along the shoreline and most noticeably on a
gently shoaling beach withdraws some 20 min before the arrival of the tsunami.
Such withdrawal is in response to the trough ahead of the wave itself and would
create both an unusual sound as well as an unusual smell. Both signals could
have been detected by the nearby elephants. Whether and how the elephants
acquired memory of such precursor events is unknown. It is possible that
precursor signals in the earth’s crust (S-waves, Love, and Rayleigh waves),
which would all have arrived within 15 min of the earthquake and more than
an hour before the tsunami, could have alerted, but not panicked the elephants.
The combination of sound and smell signals, however, may well have triggered
a response (Garstang, 2009).
Kelley and Garstang (2013) have shown that infrasound produced by thun-
derstorms generates sound waves with pressure levels that elephants can detect
at distances as great as 150 km (93 mile) from the storms.
Lindeque and Lindeque (1991) have suggested that elephant herds in eastern
fore any of the other herd animals such as wildebeest and zebra begin to move.
70 Elephant Sense and Sensibility
It is now possible to speculate that these movements are initiated by the audio
detection of remote thunderstorms heralding the end of the dry season.
Research at the University of Virginia, together with work being done at the
universities of Utah, Texas A&M, and Cornell, is exploring this relationship
between elephant movements and the occurrence of rainfall. Results show that
a distinct shift in movement of the herd occurs when rain begins to fall after a
prolonged (month’s) dry season at a location hundreds of kilometers from these
elephants (Garstang et al., 2014; Kelley and Garstang, 2013).
Garstang and his colleagues (2014) and Kelley and Garstang (2013) sug-
gest that elephants detect the low-frequency sounds generated by these distant
rainstorms, know that these signals mean that the wet season rains have started,
and change their movement behavior in response to these signals. The elephants
studied by Garstang and his colleagues in the far western Kunene region of
Namibia did not exhibit major changes in movement such as migrations out of
the area toward the rains, but rather showed changes in direction and distances
traveled in daily movements.
It is entirely possible that not only are elephants aware of the distant rain-
storms but that they are also aware of the relationship between rainfall, river
catchments, and runoff in the ephemeral rivers of northwestern Namibia and the
greening of the vegetation.
Garstang et al. (2014) further found that although the elephants change their
movement patterns in apparent response to distant rainstorms, these changes are
not consistently reflected in all of the elephant herds that were tracked nor in
fact responded to by all herds with members carrying GPS collars. This absence
of a consistent and uniform response emphasizes the difficulties faced when at-
tempting to understand animal behavior, once again reflecting that absence of
evidence is not evidence of absence.
Cyril Christo and Marie Wilkinson, in their book Walking Thunder (Christo
and Wilkinson, 2009), relate a Turkana
legend from northern Kenya in which
the sighting of an elephant is a sign that rain is imminent. They also found that
further south in Kenya, the Samburu people believe that elephants know when
rain is coming. The Samburu say that the sudden reappearance of elephants,
after months of no rain, signals the coming of the rains. Christo and Wilkinson
also note that in India the elephant was believed to bring the monsoon rains
and considered the elephant to be allied with cumulus clouds. The insight dis-
played by people living close to animals reflects the depth, if not the explana-
tion, of their observations. We should not discard the observations of these
various peoples because we perceive the explanation offered to be lacking or
inadequate.
A lone female African elephant, possibly a forest elephant ( Loxodonta cy-
clotes), who came via Brussels, Belgium, had wound up in the Lahore Zoo
in Pakistan (R. Garstang, personal communication, 2002). It is likely that
this elephant had never had a companion and never vocalized unless a 747
Boeing aircraft took off at the Lahore airport some 15–20 km (9–12 mile) away.
Communication Chapter | 9 71
She then responded with low-frequency rumbles, almost certainly triggered by
the wake vortices of the 747 engines, which generate considerable infrasound.
Poole and her colleagues (2006) report that a 10-year-old female African
savanna elephant living some 3 km (1.9 mile) from a Kenyan highway imitates
the low-frequency engine sounds made by heavy trucks. The sounds she makes
statistically match the engine sounds and are different from normal elephant calls.
Poole also reports on a 23-year-old African elephant living in captivity with two
female Asian elephants who has learned to chirp like the Asian elephants.
These findings not only demonstrate that elephants are capable of vocal
learning, imitating signals not typical of their species, but suggests that their
vocal learning capabilities reflect selective evolutionary pressure that affects
their social relationships.
Elephants that have been exposed to culling where helicopters and firearms
have been used are fully aware of the meaning of the sounds generated by these
sources. In the Kruger National Park, in particular, culling operations were con-
ducted near sunset in order to take advantage of cool conditions. We now know