Elephant Sense and Sensibility

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by Michael Garstang


  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
r />   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

  Etosha National Park in Namibia head toward the Caprivi Strip 2–3 weeks be-

  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

 

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