In the red howler there is one context in which
verbal abuse serves no purpose - when several males from a rival
group gang up to try and take over another group's females by
kicking out the males. During such invasions the generally placid
demeanour of the average howler is completely cast off and a savage
bout of fighting may result in severe injury or even death. Just
who wins generally seems to depend on the extent of mutual
cooperation between either the invading or defending males:
aggressive or defensive pacts between males on either side are
seemingly vital in deciding the outcome. If successful, the raiders
may consolidate their newly won position of sexual dominance over
the group's females by killing one or more of the vanquished males'
offspring. Such instances of infanticide are probably far more
common among primates than had been thought, even being recorded in
such generally peaceful animals as Milne-Edwards diademed sifaka,
and it may be standard procedure under certain circumstances in
Hanuman langurs.
In howler monkey society males rank above females
and young adults above their elders, who gradually descend the
status ladder as they grow older; immature juveniles, however, rank
lowest of all. Normally there are few outward signs of this
dominance hierarchy except when a subordinate gives way to a
superior in matters such as access to food. The muriqui of Brazil's
remnant Atlantic coast rainforests - the largest of the South
American monkeys - also seems to reinforce the view that large size
goes hand in hand with a placid lifestyle in arboreal primates for
which leaves are the main form of sustenance. Muriqui groups may
contain up to thirty-four members of both sexes. The males seem to
get on particularly well with one another - any one male seldom
allows himself to drift away from another by more than 5 m or so,
and male-male relations are closer in this species than in any
other primate. In fact a general feeling of harmony seems to
pervade the entire group and belligerence of any kind is extremely
rare, even when access to drinking or feeding sites is at stake.
Even lengthy mating sessions (up to eighteen minutes at a time)
between group members seem to generate none of the annoying
curiosity or even outright interference which can make the love
life of some other primates, especially baboons, so vexacious and
difficult to consummate in peace. This is not the only unusual
aspect of muriqui society, for it is the females who habitually
leave the group of their birth and join another, leaving the males
behind to constitute the stable nucleus of the group. Such a system
is rare in primates; a further example is the red colobus, although
in that species the males also show some roving tendencies. Female
emigration is also found in the gorilla: a female may move home of
her own accord, lured away when a neighbouring group comes close
enough to effect the switch. She may possibly move on again later,
trying several groups before finally settling down. In chimpanzee
society, however, the females are generally coerced into leaving
the group by pressure from other members. Generally, though, in
most primate societies it is the males who are the emigrants.
In some multi-male societies the dominant males
employ eye- catchingly explicit methods of demonstrating their
superiority to a subordinate without having to prove the point by
picking a fight. In the savannah-living vervet monkey the alpha
male flaunts his genital region as a kind of 'badge of office'. In
this species the scrotum is a conspicuous powder blue, against
which the scarlet penis shows up particularly well when fully
extended. To complement this vivid display there is a patch of red
skin at the base of the tail, and below that a patch of white fur.
A high-ranking male of a mind to reduce a subordinate to a state of
cringing submission needs merely to stand up high on his rearlegs
and strut in a cocksure manner around the inferior, who adopts a
suitably hunched posture in response. As the alpha male circles,
the grovelling object of his visual put-down also turns, but at a
slower rate, constantly keeping the brilliant genital display in
sight. The subordinate also keeps his own genitals well out of
harm's way by retracting the scrotum into his body and keeping his
rear end pointed well away from his circling tormentor. This
protective attitude towards his vulnerable genitals may be crucial,
as alpha males have a habit of eliminating once and for all a
subordinate's future prospects as a sexual competitor by dashing in
and taking a quick and conclusive bite at a carelessly exposed
scrotum.
This little drama is the so-called 'red, white
and blue display', which has been seen being given (with various
small differences in detail) by vervets over a wide area. For
example in Natal the displayer holds his tail in a curve in order
to avoid spoiling the impact by covering his genitals; in Kenya the
tail is held erect like a pleased cat. There are also variations
from area to area, in the actual mode of giving the display,
indicating that social behaviour in the vervet, as in most
primates, is not set in tablets of stone but is able to respond to
local conditions. During the red, white and blue display the
recipient is normally thoroughly intimidated and cringes, giving
vent to submissive wails and casting rapid nervous glances at the
strutting performer. The latter uses his performance to reinforce
his right of access to the females, a vital consideration in any
multi- male group in which constant militant competition for mating
rights could be potentially lethal for the participants and
destructive of group cohesion. Indeed, when the females actually
come into oestrus mere visual exhibitions alone may no longer be
powerful enough to prove superiority. When this happens a real and
very nasty fight may be the only way of sorting out the winners and
losers; it can result in some unpleasant injuries, especially to
such vital equipment as the genitals.
In wedge-capped capuchins (Cebus olivaceus) the
dominance hierarchy among the females can lead to a rather unusual
technique for 'pulling rank' by some of the more dominant
individuals: parasitic nursing behaviour. Infant primates are often
born hustlers and will routinely try and hijack a meal of milk from
a 'foreign' nipple if one happens to be handy and there is a chance
of getting away with it, and there is often a good chance of that.
However, in the wedge-capped capuchin it is high-ranking adult
females who poach milk under duress from their low-ranking
companions. The latter do not appear to take kindly to such an
infringement of their privacy and exhibit distinct signs of
distress, but they have to sit and suffer as they are in no
position to do anything about the situation without risking
punishment, though thankfully such forced nursing episodes are
normally short-lived. The reason for this strange behaviour is
unclear; it may simply be a rare but regularly practised method of
emphasizing status among the females.
The desire to avoid retaliation when approaching
a superior has led to the evolution of a peculiar kind of behaviour
in both barbary macaques and savannah baboons. In most primate
societies the young juveniles are sacrosanct and can behave in the
most outrageous way with even the most senior members of the group
without fear of reprisal. A special spot of colour or brightly
coloured pelage may be the key which switches on this tolerant
response; or, more likely, switches off the normal aggressive
reaction. Males of three subspecies of Papio cynocephalus have
frequently been observed using infants as 'passports' to approach
another male, often one in consort with a female, without fear of
being beaten up. The infant is treated casually or even quite
roughly by its kidnapper, being picked up and treated as a
necessary object with a useful role to play in allowing a close
approach in safety. The precise reason for this infant-napping is
difficult to establish, as the guilty party may use his reluctant
safe- conduct pass merely to approach the superior male and not
make any physical contact.
Similar behaviour is seen in the barbary macaque,
although in this species the young are quite closely involved with
the adult males, even to the extent of sometimes being given lifts
on their backs. However, when exploited as an aggression deflector
a young juvenile in his clutches allows a subordinate male to
approach a superior without risk of attack, and such baby borrowing
is quite common in this species.
With few exceptions an infant is generally only
treated with tolerance by males within its own group. One or more
of these will probably have fathered all the resident juveniles, so
showing tolerance makes good sense. However, there are records of
infanticide within a group, although the circumstances which bring
this about are seldom clear. For example, up to 1984 infanticide
had been observed in chimpanzees once in the group at Budongo
Forest, Uganda, seven times at Gombe Stream in Tanzania and six
times at Mahale National Park in the same country. These episodes
fall into three categories: the killing of an infant in one group
by males from another; the killing of an infant (almost always a
male) by males of its own group; and the killing of an infant by a
female of its own group. Just why males should kill infants in
their own group is a mystery, as chimpanzees' social arrangements
decree that all or most of the infants within a group will have
been sired internally. This suggests that the murderers are almost
certainly killing their own offspring, a most peculiar act from a
genetic point of view. In one case at Mahale, however, the
attacking males may have been under the impression that the
slaughtered infant had been sired by a male from another group, as
the mother had been absent for a time, but observers' records
suggest that this was incorrect and the most likely father was
among the killers. The actual act in this instance was rather
gruesome, and the mother suffered a considerable mauling in her
efforts to protect her offspring by using her body as a shield. In
most cases of chimpanzee infanticide the triumphant killers end up
by eating their grisly trophy. In one well- observed instance the
victim's brother begged for and received some of the meat from his
brother's corpse- just part of a general feast in which several
females also enjoyed various bloody titbits from the still warm
body of the murdered infant.
Infanticide in species exhibiting the 'one-male'
form of social system is perhaps a little easier to explain. In
one-male groups a single male tries to defend access to a varying
number of females against invading males from other groups intent
on supplanting him. This form of society is found in species as
varied as Geoffrey's spider monkey, agile mangaby, guereza and
gorilla. In the widespread and highly successful Hanuman langur,
one-male groups occur alongside multi-male and all-male groups. In
multi- male outfits there may be a gradual and peaceful leadership
succession which does not involve the death of any of the group
members. By contrast, lone males trying to defend their exclusive
property may enjoy little success against the kind of determined
cooperative offensive which seems typical of this species. In one
encounter which was closely watched a group of males attacked
another group containing a single male accompanied by nearly thirty
females and immatures. Despite their best efforts to defend their
babies three females lost their offspring to the invading males,
one of whom subsequently supplanted the resident male who had been
ineffectual in countering such a concerted onslaught. Bereft of
their progeny the bereaved mothers soon offered themselves to their
new master and mated, giving birth to his issue a few months later.
To us the females' actions may seem incredibly heartless - but
after all, they do not want a cissy for a mate who may waste their
reproductive potential by fathering a succession of equally gutless
offspring lacking the ruthless determination necessary to depose a
group leader and sire a line of offspring for themselves. So it is
logical to make overtures to a male who exhibits all the signs of
being one of life's winners.
A new leader normally harasses some of the other
infant-bearing females soon after his conquest, but his
baby-killing endeavours require skill and cunning as he has to
reckon with the rest of the females who will often gang up to beat
him off. Such attempts to weed out a predecessor's offspring after
a takeover seem to be more common than pre-takeover infanticide.
However, the latter situation has a greater chance of success if
several males act in consort to overwhelm the opposition. This
makes it easier to track down the mothers, who normally quickly see
what is coming and do their best to hide away from the would-be
killers of their babies. Some of the older females may have seen it
all before and know the mortal danger to their offspring posed by
the invading band of males. After all, their current lord and
master probably won his job in the same way, and their new leader
can probably only look forward to a tenure of around two years
before he in turn is toppled in a cycle of takeovers which seems to
typify Hanuman langur society.
The reasons for such acts of infanticide have
been disputed, but seem to involve an acceleration of the coming
into oestrus of the bereaved females. They would otherwise not be
sexually receptive while still nursing babies which to the new
master are not only superfluous to requirements but potential
competitors. Similar takeovers accompanied by infanticides also
occur in several other monkey species, including blue- and
red-tailed monkeys in Africa and silvered and purple-faced langurs
in Asia.
Hanuman langur society eventually settles down
after such a traumatic episode and apart from this the females lead
very stable lives, forming the nucleus of the group over long
periods. Although there is an age- related dominance hierarchy
among them (young mature animals gain dominance over their older
colleages, and then drop down through the hierarchy as they too
age) they spend a lot of time grooming one another in matronly
harmony. This friendly accord also extends to the great indulgence
shown towards handling one another's young, even when newly born.
This is a common trait among the colobines and quite the opposite
of most cercopithecine mothers, who exhibit extreme protectiveness
of their offspring until they reach quite an advanced age.
Gorilla family life generally seems to be very
amicable: the silverback group leader may groom his females as well
as enjoying their attentions. He also shows extreme tolerance
towards the youngsters in his group as they playfully clamber over
his body. In fact his giant figure seems to be a positive
attraction for juveniles of varying ages, who seem irresistibly
drawn towards him in a bid to sit near him or even groom him. On
the other hand, lone males intent on wife theft will bulldoze their
way into a group and abduct a female after first getting her infant
out of the way by killing it.
Patas monkey males seem to lead rather lonely
lives, despite being the head of a group of females and offspring.
The females appear to be notably anti- male for much of the year,
actually threatening their leader if he comes close. They only
reveal any clear signs of friendliness when they come into oestrus,
when it is they who solicit his attentions. The group leader's
wives, by contrast, lead very gregarious and affable lives
featuring long grooming sessions and a great deal of mutual
baby-sitting. Patas males too form single-sex groups in which they
enjoy a much richer social life, forming close bonds with certain
selected companions. What a marked difference from the isolated
life of the leader in a mixed group, who seems to pay the price for
sexual success by becoming almost a social outcast. Patas monkeys
roam over enormous ranges in their dry savannah environment - up to
38.5 sq km (15 sq miles) has been reported - and when neighbouring
groups make the occasional chance meeting they try to avoid any
contact. The only exception happens during the breeding season,
when rival males may raise the temperature somewhat by making
aggressive chases and postures towards the other side.