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Slotow, R., Van Dyk, G., Poole, J., Page, B., Klocke, A. Older bull elephants control young males: Orphaned male adolescents go on killing sprees if mature males aren’t around. Nature. 408: 425-426.

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Abstract and Figures

Musth is a state of heightened sexual and aggressive activity in male elephants. Between 1992 and 1997, young orphaned musth male African elephants (Loxodonta africana) that had been introduced to Pilanesberg, South Africa, killed more than 40 white rhinoceros (Ceratotherium simum). The killing ceased after six older male elephants were introduced from the relatively normal Kruger Park population. The deviant behaviour of the young Pilanesberg males was rectified by the consequent reduction in musth.
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usth is a state of heightened sexual
and aggressive activity in male ele-
. Between 1992 and 1997,
young orphaned musth male African ele-
phants (Loxodonta africana) that had been
introduced to Pilanesberg, South Africa,
killed more than 40 white rhinoceros (Cera-
totherium simum). The killing ceased after
six older male elephants were introduced
from the relatively normal Kruger Park
population. The deviant behaviour of the
young Pilanesberg males was rectified by
the consequent reduction in musth.
Musth, during which males experience
dramatic surges in circulating testos-
, is characterized by a distinct pos-
ture, swollen and secreting temporal glands,
urine dribbling, and increased sexual and
aggressive behaviour
. Males gradually enter
musth as they become bigger and more
experienced and better at winning encoun-
ters with other males
. In natural popula-
tions musth first occurs between 25 and 30
years of age
and its duration increases with
age (for age 25–30 years, musth lasts from
days to weeks; at 31–35, it lasts for several
weeks; at 36–40, for 1–2 months; and after
40 years of age, 2–4 months)
Young orphan elephants of less than ten
years old were reintroduced to Pilanesberg
in the 1980s. These were the survivors of
Kruger Park culls and they matured in the
absence of adult males. Males were breeding
successfully by 18 years old and were enter-
ing musth from that age. Musth lasted for
up to five months, an unusually long time
even for males of more than twice that age
In Amboseli, Kenya, young male ele-
phants were found to be significantly less
likely to be in musth if a larger musth male
was present
. Young males also lose the
physical signs of musth minutes or hours
after an aggressive interaction with a high-
er-ranking musth male — it seems that
they are forced out of musth by repeated
encounters with older males
. By infer-
ence, larger, older males may delay the
onset of musth in younger males.
We tested this idea by introducing six
older males to Pilanesberg’s population of
about 85 elephants, which included 17
young males aged between 15 and 25 and
independent of family groups. Musth had
been recorded in six of these 17. We expect-
ed musth in the original young males to
become shorter, the onset of first musth to
be delayed and, with deviant behaviour
being controlled by a reduction in rank,
fewer rhinoceros to be killed.
Musth duration in young males declined
significantly after the older Kruger Park
males were introduced to Pilanesberg
(Table 1 and Fig. 1; Wilcoxon paired signed
ranks test: z411.826, 1-tailed P40.034).
Indeed, musth was shorter in all males, and
musth periods of males entering musth for
the first time were also significantly reduced
(Table 1; Mann–Whitney U-test: z411.938,
1-tailed P40.027) after the introduction.
The two most extensive periods of
musth in the original males occurred when
no Kruger Park males were in musth (Fig.
1). Bull 5, the largest original male, was only
in musth when Kruger Park males were not;
his second musth period was substantially
shortened, his third was further reduced,
and in 2000 it was delayed by two months
(Table 1; Fig. 1).
Despite our small sample sizes, these
results provide strong support for the idea
that older males suppress musth patterns in
younger males
. Assessment theory
dicts that selection should favour individu-
als who are able to assess the physical and
behavioural traits of rival males and use this
knowledge of the costs and benefits of fight-
ing and the probability of winning to adjust
their own behaviour.
A strategy of dropping out of musth
when confronted with aggression from
higher-ranking musth males increases
immediate survival, and therefore long-
term reproductive fitness. Some experience
may be necessary for behavioural control
under musth, and its gradual acquisition
brief communications
VOL 408
23 NOVEMBER 2000
| 425
Older bull elephants control young males
Orphaned male adolescents go on killing sprees if mature males aren’t around.
Table 1 Effect of introducing older males on musth in young Pilanesberg males
Bull Musth before introduction Musth after introduction
Dates Duration (days) Dates Duration (days)
1 23 Mar–27 Jun 1996 ¤95 Culled before introduction
18 18 Aug–4 Sep 1996 ¤16 17–23 Nov 1998 6
19 May–1 Jun 1997 ¤14 25 Feb 1999 1
6 14 Apr–8 Jun 1997 55 24–26 Jan 1999 3
29 Sep–13 Nov 1997 46 13 Apr 1999 1
8–19 May 1999 12–26
22 Apr–Jul 1997 `90 3–4 Dec 1998 2
12 Oct 1997–6 Jan 1998 ¤86 20 Nov 1999–12 Jan 2000 53–77
20 Aug 1997 Unknown Culled before introduction
5 4 Jan–18 May 1998 134 6 Jan–21 Mar 1999 76
12 Mar–5 Apr 2000 24
26 None 3–9 Oct 1998 6
24 None 2 Mar–24 Apr 1999 53
3 None 30 Sep 1999 1
There may have been undocumented periods of musth before April 1996. ‘Greater than’ sign indicates minimum periods when bulls were not seen
immediately before or after the specified dates. Ranges indicate the likely interval between the first or last date the elephant was seen in musth, and the date
when it was seen out of musth before or after those musth dates. Numbers in bold were used in paired analysis.
Figure 1 Observed (black bars) and probable (white bars) musth periods of elephants identified by number. Kruger Park males (bulls
30–35, bold type) were introduced to Pilanesberg (25° 158 S, 27° 058 E) between 6 February (vertical line) and 21 March 1998. Shaded
areas indicate periods when at least one Kruger male was in musth. Only Pilanesberg males (bull numbers not in bold) that entered
musth are shown. The original elephant population was brought from Kruger in 1981 (13 juvenile males, 5 juvenile females), 1983 (13
juvenile males, 11 juvenile females) and 1993 (19 males, 17 females) and from Namibia in 1982 (1 juvenile male, 1 juvenile female). The
first calf was born in 1989, showing that males began breeding at about 18 years. Additional details are available from the authors.
Bull 3
Bull 26
Bull 24
Bull 5
Bull 6
Bull 22
Bull 18
Bull 20
Bull 1
Bull 33
Bull 30
Bull 35
Bull 34
Bull 32
Bull 31
1996 1997 1998 1999
© 2000 Macmillan Magazines Ltd
*School of Life and Environmental Science,
George Campbell Building, University of Natal,
Durban 4041, South Africa
North West Parks and Tourism Board, Pilanesberg
National Park, PO Box 1305 Mogwase, South Africa
PO Box 24747, Nairobi, Kenya
1. Poole, J. H. & Moss, C. J. Nature 292, 830–831 (1981).
2. Poole, J. H. Behaviour 102, 283–316 (1987).
3. Poole, J. H., Kasman, L. H., Ramsay, E. C. & Lasley, B. L.
J. Reprod. Fert. 70, 255–260 (1984).
4. Rasmussen, L. E. L., Hall-Martin, A. J. & Hess, D. L. J. Mammal.
77, 422–439 (1996).
5. Poole, J. H. Anim. Behav. 37, 140–152 (1989).
6. Parker, G. A. J. Theor. Biol. 47, 223–243 (1974).
7. Maynard-Smith, J. & Parker, G. A. Anim. Behav. 24, 159–175
least number and degree of fused pentagons
out of the 4,478 possible isomers (see Sup-
plementary Information).
C NMR spectrum of Sc
shows five highly deshielding lines above
151 p.p.m. up to 167.9 p.p.m. These unusual
C NMR lines stem from those carbon
atoms on the fused-pentagon area. In par-
ticular, the two lowest lines at half intensity
(numbers 16 and 17 in Fig. 1a) originate
from the four carbon atoms that connect
two pentagonal rings.
The Sc
structure (Fig. 1c) contains
two pairs of two-fold fused pentagons with
two closely situated scandium atoms. The
observed Sc–Sc distance is 2.87(9) Å,
indicative of the formation of a Sc
inside the C
cage. Endohedral metallo-
fullerenes are stabilized by intrafullerene
electron transfer
; there are 40.0(2) e
electrons in the area corresponding to the
dimer calculated from the MEM charge
density, a value that is very close to (Sc
with 40 e. The ab initio calculation also
indicates that the Sc
dimer donates two
electrons to the C
cage, resulting in a for-
mal electronic state of (Sc
. It is
this charge-transfer interaction between the
dimer and the fused pentagons that sig-
nificantly decreases the strain energies
caused by the pair of fused pentagons and
thus stabilizes the fullerene cage. We con-
clude that the isolated-pentagon rule is not
necessarily a test for stable geometry in
endohedral metallofullerenes
Chun-Ru Wang*, Tsutomu Kai*,
Tetsuo Tomiyama*, Takuya Yoshida†,
Yuji Kobayashi†, Eiji Nishibori‡,
Masaki Takata‡, Makoto Sakata‡,
Hisanori Shinohara*
VOL 408
23 NOVEMBER 2000
may acclimatize males physiologically and
psychologically to the extremely high levels
of circulating testosterone
This translocation ended the killing
of rhinoceros by elephants. Introducing
higher-ranking males may help in other
reserves containing Kruger orphans where
managers face similar problems. In ele-
phant populations that have experienced
massive poaching, the hunters’ selection of
larger males may cause similar problems
once rhinoceros populations increase, and
these too may be helped by importing older
male elephants.
Rob Slotow*, Gus van Dyk†, Joyce Poole‡,
Bruce Page*, Andre Klocke*§
brief communications
Materials science
fullerene encaging a
scandium dimer
he geometry of carbon cages
(fullerenes) is governed by the isolated-
pentagon rule (IPR)
, which states
that the most stable fullerenes are those in
which all pentagons are surrounded by five
hexagons. Although this rule has been veri-
fied experimentally
, it is impossible for
fullerenes in the range C
to C
to obey it.
Here we describe the production and char-
acterization of an IPR-violating metallo-
fullerene, Sc
, a C
fullerene encaging
a scandium dimer. Our results indicate that
encapsulation of the metal dimer signifi-
cantly stabilizes this otherwise extremely
unstable C
We generated soot containing Sc
and other scandium metallofullerenes
direct-current arc discharge of scandium/
graphite composite rods under a flow of
helium. Sc
metallofullerene was iso-
lated using multistage high-performance
liquid chromatography
. Starting with 800 g
arc-generated soot, we were able to isolate
about 2.0 mg Sc
. The purity (99.8%)
of this material was confirmed by laser-
desorption time-of-flight mass spectrometry.
There are several ways in which the IPR
can be violated, the most straightforward
being to generate the so-called ‘fused-penta-
gon’ in which pentagons are adjacent to one
another. For 66-atom carbon cages with
hexagonal and pentagonal faces, there are
4,478 possible (non-IPR) structural isomers
with 22D
, 12C
, 182C
, 1122C
and 4,1342C
. Consid-
ering the observed 19-lines (522; 1424) in
the high-resolution
C NMR spectrum of
(Fig. 1a), only eight structural iso-
mers of C
with C
symmetry can satisfy
C NMR pattern.
To determine the geometrical structure
of the metallofullerene unambiguously, we
made synchrotron X-ray powder diffraction
measurements on Sc
at SPring-8
BL02B2. The MEM (maximum-entropy
three-dimensional electron-den-
sity distribution of Sc
obtained by the
MEM/Rietveld procedure
using synchro-
tron X-ray diffraction is shown in Fig. 1b,
together with an optimized geometry of
based on non-local density-func-
tion B3LYP/Basis set [Sc(LanL2DZ); C(3-
21G)] calculations (Fig. 1c).
The Sc
X-ray crystal structure is of
space group Pmn2
(no. 31), where a is
10.552(2) Å, b is 14.198(2) Å, c is 10.553(1)
Å, and the reliability factors of the final
Rietveld fitting were R
42.4% and
413.1%. The final charge densities ob-
tained by the maximum-entropy method,
whose reliability factor is R
45.4%, reveal
a pair of two-fold fused pentagons on a
cage that encapsulates a Sc
the most stable Sc
structure has the
Figure 1
C NMR and synchrotron X-ray powder diffraction structural data on Sc
. a,
C NMR spectrum of Sc
in CS
(2.5 mg Cr(acac)
, where ‘acac’ represents acetylacetonate, relaxant and C
lock) after 160,000 scans at room temperature using a
Varian Inova 600 spectrometer at 600 MHz. The five lines marked with an asterisk are half the intensity of the other 14 full lines (131.6,
132.1, 137.9, 138.4*, 139.3, 140.1, 142.0, 143.3*, 143.5, 144.7, 144.9, 145.2, 146.7, 150.4, 153.9*, 159.8*, 164.1*, 164.4 and
167.9 p.p.m.). b, X-ray structure of the IPR-violating Sc
fullerene, showing a top view along the
axis and a side view. The equi-
contour (1.4
) surface of the final maximum-entropy method electron charge density is shown; the Sc
dimer is in red and the two
pairs of fused pentagons are evident. The X-ray powder pattern had good counting statistics and was measured in an X-ray powder
experiment using synchrotron radiation and imaging-plate detectors exposed for 2 h (incident X-ray wavelength, 0.75 Å). The X-ray pow-
der pattern of Sc
was obtained with a 0.02º step up to 20.3º in 2
, which corresponds to 2.0 Å resolution in
spacing. c, Calculat-
ed Sc
structures (see text).
© 2000 Macmillan Magazines Ltd
... Such visual and olfactory displays reflect the signallers hormonal, status, condition and physical strength (Clutton-Brock & Huchard 2013). Research on elevated testosterone levels in Asian and African elephant males suggests that musth contributes towards the "smooth functioning of male elephant society" as musth males are dominant over non-musth males, and musth in bigger, older bulls suppresses reproduction (musth) and aggression in younger males (Slotow et al. 2000), with chemosignals in musth varying with age, dominance and reproductive status (Greenwood et al. 2005). Male African elephants can distinguish conspecific female urine collected at the time of ovulation from urine obtained at the mid-luteal time of the estrous cycle . ...
... Further, scent marks containing relatedness markers could be used to monitor levels of hybridization and inbreeding, 6. Translocation and relocation programs -semiochemicals that promote social stability are of interest. One study showed that the presence of old mature musth bulls controls the behaviour of younger rogue males (Slotow et al. 2000). It is as of yet unclear whether semiochemicals in female exudates provide a similar function. ...
... ss morphology, functions, comparative anatomy, and evolution. Brain Res. Bull. 70, 124-157. doi: 10.1016/j.brainresbull.2006 Silk, J.B., Beehner, J.C., Bergmann, T.J., Crockford, C., Engh, A.L., Moscovice, L.R., Wittig, R.M., Seyfarth, R.M. (2010). Strong and consistent social bonds enhance the longevity of female baboons. Curr. Biol. 20, 1359-1361. Slotow, R., van Dyk, G., Poole, J., Page, B., Klocke, A. (2000. Older bull elephants control young males. Nature 408, 425-426. Smart, L.E., Aradottir, G.I., Bruce, T.J.A. (2014). Role of semiochemicals in integrated pest management. Integrated pest management: current concepts and ecological perspective. Elsevier Academic Press Inc, San Diego Stoeger A.S., Manger, P. (2014). Vocal learning in eleph ...
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... For example, the support that 45 cooperative breeding species receive from non-breeding helpers may lead to longer lifespans than 46 those of related solitary species [1]. The transfer of enhanced ecological knowledge to close 47 4 disease or trophy hunting can disrupt intergenerational flow of accumulated social and ecological 83 knowledge, impeding collective movement and the ability to locate critical resources [4,[37][38][39][40]. 84 The age structure of a group can also regulate the behaviour of younger individuals [41,42], 85 influencing aggression rates and social cohesion [43]. The impact of diminished cohorts of 86 younger individuals on higher-order network structure is less well understood, but likely to have 87 repercussions for network connectivity and cohesiveness given that younger adults are more into old age [6,32,54]. ...
Ageing affects many phenotypic traits, but its consequences for social behaviour have only recently become apparent. Social networks emerge from associations between individuals. The changes in sociality that occur as individuals get older are thus likely to impact network structure, yet this remains unstudied. Here we use empirical data from free-ranging rhesus macaques and an agent-based model to test two things: (1) how age-based changes in social behaviour influence an individual's level of indirect connectedness in their network, and (2) how social ageing feeds up to affect overall network structure. Our empirical analyses revealed that female macaques became less indirectly connected as they aged for some, but not all measures examined, suggesting that ageing animals can remain well integrated in some social contexts. Our agent-based model showed that aged-based changes in social behaviour can scale up to the network level. Networks with a higher proportion of old individuals were less connected and less cohesive. We did not find similar effects of age distribution on the structure of empirical networks, which may reflect limited age variation in our data. Overall, our results suggest a potentially important and underappreciated role of age in the structure and function of animal collectives.
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... These impacts extend beyond the immediate and direct loss of individual animals to having a lasting and profound effect on population integrity because of compromised development and impaired social relationships [26]. For example, male African elephants orphaned as a result of culling and translocation operations in the 1970s and 1980s demonstrated a tendency for hyperaggressive behaviour on reaching sexual maturity [27,28], while females and their family groups exhibited impaired social knowledge decades after these traumatic events [29]. Furthermore, poaching events in East Africa led to the formation of orphan groups of elephants that commonly consist of unrelated individuals, demonstrate weaker social relationships and rarely benefit from associating with older and more experienced individuals [30][31][32]. ...
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The transmission of reliable information between individuals is crucial for group-living animals. This is particularly the case for cognitively advanced mammals with overlapping generations that acquire detailed social and ecological knowledge over long lifetimes. Here, we directly compare the ecological knowledge of elephants from two populations, with radically different developmental histories, to test whether profound social disruption affects their ability to assess predatory threat. Matriarchs (≤50 years of age) and their family groups received playbacks of three lions versus a single lion roaring. The family groups in the natural Amboseli population (Kenya) reliably assessed the greater predatory threat presented by three lions roaring versus one. However, in the socially disrupted Pilanesberg population (South Africa), no fine-scale distinctions were made between the numbers of roaring lions. Our results suggest that the removal of older and more experienced individuals in highly social species, such as elephants, is likely to impact the acquisition of ecological knowledge by younger group members, particularly through the lack of opportunity for social learning and cultural transmission of knowledge. This is likely to be exacerbated by the trauma experienced by juvenile elephants that witnessed the culling of family members and were translocated to new reserves. With increasing levels of anthropogenic disturbance, it is important that conservation practitioners consider the crucial role that population structure and knowledge transfer plays in the functioning and resilience of highly social and long-lived species.
... For males who survived past independence but who had yet to experience musth (n = 109), we included their age at the end of the sample period or death as censored in a Cox proportional hazard regression model for time to event analysis. We counted the number of musth-age male competitors (>35 years old), who had well established musth periods and could therefore potentially suppress other males' musth onset as these older males were larger and socially dominant (Hall-Martin and van der Walt 1984;Poole 1989;Slotow et al. 2000). We compared factors influencing time to first musth using the Cox's proportional hazards regression, with a forward (Wald) model. ...
Cohort effects, reflecting early adversity or advantage, have persisting consequences for growth, reproductive onset, longevity, and lifetime reproductive success. In species with prolonged life histories, cohort effects may establish variation in age-sex structures, while social structure may buffer individuals against early adversity. Using periods of significant ecological adversity, we examined cohort effects for male and female elephants (Loxodonta africana) over almost 50 years in Amboseli, Kenya. Mortality spiked during severe droughts with highest mortality among calves under 2 years and females over 40 years. Deaths of oldest females resulted in social disruption via matriarch turnover, with potential impacts on resource acquisition for survivors. We predicted that survivors of high mortality and social challenges would have altered life-history trajectories, with later age at first reproduction and reduced age-specific fertility for females and slow transitions to independence and late-onset of potential mating or musth among males. Contrary to expectations, there were no persisting early drought effects on female age at first conception while matriarch loss around puberty accelerated reproductive onset. Experience of an early life drought did not influence age-specific reproductive rates once females commenced reproduction. Males who survived an early drought exhibited complex consequences: male age at family independence was later with larger peer cohort size, but earlier with drought in year of independence (13.9 vs 14.6 years). Early drought had no effect on age at first musth, but male reproductive onset was weakly associated with the number of peers (negative) and age at independence (positive).
... The interactions among individuals with diverse social roles across social tiers manifests as fission-fusion dynamics in response to changing sociophysical landscape [19,67]. Poaching-which during the militarized wave of the past decade eliminated large subsets of populations including mature and immature elephants [68] -impacts demography [69], resource acquisition [70,71] population genetics [72] and various social behaviors [73,74] in targeted populations. ...
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Selective harvest, such as poaching, impacts group-living animals directly through mortality of individuals with desirable traits, and indirectly by altering the structure of their social networks. Understanding the relationship between disturbance-induced, structural network changes and group performance in wild animals remains an outstanding problem. To address this problem, we evaluated the immediate effect of disturbance on group sociality in African savanna elephants-an example, group-living species threatened by poaching. Drawing on static association data from ten free-ranging groups, we constructed one empirically based, population-wide network and 100 virtual networks; performed a series of experiments 'poaching' the oldest, socially central or random individuals; and quantified the immediate change in the theoretical indices of network connectivity and efficiency of social diffusion. Although the social networks never broke down, targeted elimination of the socially central conspecifics, regardless of age, decreased network connectivity and efficiency. These findings hint at the need to further study resilience by modeling network reorganization and interaction-mediated socioecological learning, empirical data permitting. The main contribution of our work is in quantifying connectivity together with global efficiency in multiple social networks that feature the sociodemographic diversity likely found in wild elephant populations. The basic design of our simulation makes it adaptable for hypothesis testing about the consequences of anthropogenic disturbance or lethal management on social interactions in a variety of group-living species with limited, real-world data.
Early deprivation of adult influence is known to have long‐lasting effects on social abilities, notably communication skills, as adults play a key role in guiding and regulating the behavior of youngsters, including acoustic repertoire use in species in which vocal production is not learned. Cheetahs grow up alongside their mother for 18 months, thus maternal influences on the development of social skills are likely to be crucial. Here, we investigated the impact of early maternal deprivation on vocal production and use in 12 wild‐born cheetahs, rescued and subsequently hand‐reared either at an early (less than 2 months) or a later stage of development. We could distinguish 16 sound types, produced mostly singly but sometimes in repeated or multitype sound sequences. The repertoire of these cheetahs did not differ fundamentally from that described in other studies on adult cheetahs, but statistical analyses revealed a concurrent effect of both early experience and sex on repertoire use. More specifically, early‐reared males were characterized by a high proportion of Purr, Meow, and Stutter; early‐reared females Mew, Growl, Hoot, Sneeze, and Hiss; late‐reared males Meow, Mew, Growl, and Howl; and late‐reared females mostly Meow. Our study demonstrates therefore the long‐term effects of maternal deprivation on communication skills in a limited‐vocal learner and its differential effect according to sex, in line with known social differences and potential differential maternal investment. More generally, it emphasizes the critical importance to consider the past history of the subjects (e.g., captive/wild‐born, mother/hand‐reared, early/late‐mother‐deprived, etc.) when studying social behavior, notably acoustic communication.
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This study reports concentrations of testosterone and dihydrotestosterone in both serum and temporal-gland secretions of male African elephants (Loxodonta africana), including ra-diocollared elephants, and identifies a spectrum of volatile components in the temporal-gland secretions. Androgens in the serum (testosterone and dihydrotestosterone) were measured in 111 adult male African elephants, ages 21-40 years, from two national parks in South Africa during several years and seasons. About one-fifth (18.6%) of these mature, male, African elephants exhibited dramatically increased concentrations of testosterone in serum characteristic of male Asian elephants during musth. In Kruger National Park, six radiocollared male African elephants, ages 25-35 years, were tracked and serially sampled for both serum and temporal-gland secretions during a 5-year period. Concentrations of testosterone in serum and temporal-gland secretions were elevated cyclically at times when typical musth behaviors, including aggression, were observed. This study reports the first chemical characterization of the volatile compounds of the temporal-gland secretions from male African elephants in musth. It reveals many similarities between the chemical constituents of the temporal-gland secretions of these male African elephants and the compounds identified in male Asian elephants. In addition, several compounds, not previously identified in temporal-gland secretions of African elephants, are described. Such chemical data support the behavioral observations by ourselves and other researchers that male African elephants experience musth. Especially convincing are the concurrent hormonal and chemical data from the radiocollared males during episodic periods of behavioral musth. Implications of the incidence of musth in the past and present ecology of African elephants are discussed in view of the increasing compression within national parks.
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Urine samples were obtained from free-ranging African elephants that were considered to be in and out of musth. Testosterone concentrations, measured by radioimmunoassay were significantly greater in males that were in or around the time of behavioural musth. This study supports a correlation between the observed behavioural characteristics of musth and urinary testosterone levels.
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The phenomenon of musth in male Asian elephants, Elephas maximus, has long been recognized1. Musth, which has been likened to rutting behaviour in ungulates2, refers to a set of physical and behavioural characteristics displayed periodically by adult male elephants. The most obvious manifestations are a sharp rise in aggressive behaviour, copious secretions from and enlargement of the temporal glands, and the continuous discharge of urine3. It has been speculated that a similar phenomenon occurs in males of the African genus, Loxodonta africana, but most workers have concluded that it does not exist4-7. Here we show that musth does occur in the African elephant and that its manifestations are similar to those in the Asian elephant.
Male Loxodonta africana spent more time in association with females during musth than during non-musth periods. Males were more aggressive during their musth periods. Occurrence and duration of musth were age-related: no male under 24 yr was seen in musth; bouts of musth among younger individuals were short and sporadic, while older males experienced longer more predictable periods of musth on an annual basis. Males in musth were observed year-round, but frequency of musth males was highest during and following the 2 rainy seasons and, in general, good rainfall years had higher frequencies of males in musth than did poor rainfall years. Number of males in musth per month correlated closely with the number of females observed in estrus, but since estrus lasts only 4-6 days, while musth may last several months, onset of musth was not necessarily triggered by onset of estrus in a particular female. The musth periods of different males were asynchronous and each male came into musth at a specific time of year. This period was relatively consistent from one year to the next, particularly among older males. Males in musth advertised their heightened sexual and aggressive state through visual and olfactory signals and by vocalizing. These signals announce identity, condition and location to both rival males and to potentially receptive females. The physical and behavioral characteristics and temporal patterning of musth are very similar in African and Asian elephants. -from Author
Predictions derived from game theory suggest that animals should not signal their intentions during conflict situations. However, during the period of musth, male elephants,Loxodonta africana, announce a state of heightened aggression with signals that are unbluffable. Since smaller musth males in poor condition are able to dominate larger, normally higher-ranking, non-musth males in good condition, musth provides a useful system with which to examine the possibility of honest signalling of motivation, rather than of fighting ability. Despite the highly aggressive state of males in musth, escalated contests are extremely rare. The behaviour of musth and non-musth males suggests that opponents are able to estimate their often rapidly changing roles in the asymmetries with relative accuracy. Since, unlike most other rutting mammals, elephants have asynchronous sexually active periods, resource value varies both with age and the fluctuating sexual state of a particular individual. It is suggested that musth may be a case where information about resource value is conveyed.
A theoretical analysis is made of the evolution of behavioural strategies in contest situations. It is assumed that behaviour will evolve so as to maximize individual fitness. If so, a population will evolve an ‘evolutionarily stable strategy’, or ESS, which can be defined as a strategy such that, if all members of a population adopt it, no ‘mutant’ strategy can do better. A number of simple models of contest situations are analysed from this point of view. It is concluded that in ‘symmetric’ contests the ESS is likely to be a ‘mixed’ strategy; that is, either the population will be genetically polymorphic or individuals will be behaviourally variable. Most real contests are probably asymmetric, either in pay-off to the contestants, or in size or weapons, or in some ‘uncorrelated’ fashion; i.e. in a fashion which does not substantially bias either the pay-offs or the likely outcome of an escalated contest. An example of an uncorrelated asymmetry is that between the ‘discoverer’ of a resource and a ‘late-comer’. It is shown that the ESS in asymmetric contests will usually be to permit the asymmetric cue to settle the contest without escalation. Escalated contests will, however, occur if information to the contestants about the asymmetry is imperfect.
The view is examined that the adaptive value of conventional aspects of fighting behaviour is for assessment of relative RHP (resource holding power) of the combatants. Outcomes of aggressive disputes should be decided by each individual's fitness budget available for expenditure during a fight (determined by the fitness difference between adoption of alternative strategies, escalation or withdrawal without escalation) and on the rate of expenditure of the fitness budget if escalation occurs (determined by the RHPs of the combatants). Thus response thresholds for alternative strategies (“assessments”) will be determined by natural selection on a basis of which opponent is likely to expend its fitness budget first, should escalation occur. This “loser” should retreat (before escalation) and the winner should stay in possession of the resource. Many aggressive decisions depend on whether one is a resource holder, or an attacker. Assuming the RHP of the combatants to be equal, there are many instances of fitness pay-off imbalances between holder and attacker which should weight the dispute outcome in favour of one or other opponent by allowing it a greater expendable fitness budget. Usually the weighting favours the holder; the attacker therefore needs a correspondingly higher RHP before it may be expected to win. This is not invariably the case, and much observed data fits the predictions of this sort of model. If assessments are perfect and budget expenditure rates exactly predictable, then there would never seem to be any case for escalation. Escalation can be explained in terms of injury inflictions (expenditures) occurring as discrete events; i.e. as “bouts” won or lost during fighting. Assessment can give only a probabilistic prediction of the outcome of a bout. A simple model is developed to investigate escalation situations. Each combatant assesses relative RHP; this correlates with an absolute probability of winning the next bout (cabs). The stake played for is infliction of loss of RHP and is determined by the fitness budgets of the opponents. (Each individual plays for the withdrawal of its opponent.) This defines a critical probability of winning (ccrit) for each combatant, above which escalation is the favourable strategy (cabs > ccrit) and below which withdrawal is favourable (cabs < ccrit). Escalation should occur only where cabs-ccrit is positive for both combatants. This model gives predictions compatible with the observations, indicating that RHP loss alone can be adequate to explain withdrawal: escalation behaviour. Withdrawal tendency will be increased by low searching costs. Escalations should be restricted to closely matched RHP opponents if RHP disparity is the major imbalance. Outside the “escalation range” of a given individual, the higher RHP individual wins and the lower one loses (i.e. it should withdraw after conventional display). RHP disparity and holder: attacker imbalance should both interact to shape the observed pattern, though their relative importances will depend on species and situation. In some instances selection may favour immediate withdrawal from an occupied territory even without assessment of RHP.
  • L E L Rasmussen
  • A J Hall-Martin
  • D L Hess
Rasmussen, L. E. L., Hall-Martin, A. J. & Hess, D. L. J. Mammal. 77, 422–439 (1996).
  • J H Poole
  • L H Kasman
  • E C Ramsay
  • B L Lasley
Poole, J. H., Kasman, L. H., Ramsay, E. C. & Lasley, B. L. J. Reprod. Fert. 70, 255-260 (1984).