- Animals living permanently in social groups
comprising both sexes and all ages need an
efficient system of communication for conveying
information about their feelings and intentions
to other group members.
 - Scent signals
-
- Nocturnal prosimians, in their dispersed
semi-solitary groups, have few, if any, visual
signals. At night, a slow loris is just visible
to another slow loris by its white nose stripe
and contrasting dark eye patches. The face, with
its tethered upper lip, is capable of little
expression, and the stumpy tail is virtually
immobile. In nocturnal primates in general, the
closely allied senses of smell and taste are
all-important. Pheromones, products of the scent
glands, give information about the female's
reproductive cycle, probably the most important
thing one loris needs to know about another.
These are distributed by scentmarking - by
rubbing the specialized scent glands on a
branch, or by urinating on the hands and feet,
thus leaving scented footprints throughout the
range.
-
- Diurnal prosimians also depend on scent in
cornmunication and, in male ring-tailed lemurs,
the scent glands are used in a ritualized
defence of territory. A specialized scent gland
with a sharp horny spur on the inside of the
fore-arm is placed against another gland
situated above the armpit, thus mingling the
secretions. The tail is then drawn clown across
the fore-arms so that the horny spur combs
deeply into the fur, impregnating it with the
odour. The tail is then arched over the back and
moved up and clown, wafting the scent towards
the opponent in the adjoining territory. At the
saine time, the skin surrounding the genitalia
is rubbed on a convenient branch. The outcome of
this so-called 'stink-fight' is the retreat of
one or other of the contestants, and the
boundary between the groups is once again
established by peaceful means, without actual
fighting. Ring-tailed lemurs also establish
territory by scent-marking saplings, scraping
the horny spur of the fore-arm gland directly
against the bark, leaving comma-shaped marks
which are impregnated with the scent.
-
- In diurnal anthropoids, pheromones also play
an important role in communication. In New World
monkeys, specialized scent glands on the neck
and chest as well as the genital region are used
to convey information about age, sex and social
rank as well as to mark territory. In Old World
monkeys and apes, there are fewer examples of
specialized scent glands, and scent signals are
probably much less significant than visual
signals in social behaviour. The swelling of the
female's sexual skin at oestrus in some members
of this group acts as a visual signal to males,
but this is undoubtedly reinforced by scent
signals. Although in field observations the
influence of female pheromones can only be
inferred, their effect on the mating behaviour
of the male has been demonstrated in the
laboratory. The sense of smell even influences
human social behaviour but, because man is so
visually orientated, its importance is not
always appreciated.
-
- Visual signals
-
- In diurnal animals, of course, visual
communication is dominant and, with colour
vision well developed in the anthropoids, coat
colour is vital in species recognition. This is
seen particularly in forest-dwelling guenons
where striking facial patterns - contrasting
spots, tufts, blobs and stripes of colour -
accentuate the differences between closely
related species living in the same place. This
helps an animal to recognize its own kind and
thus prevent hybridization.
-
- Visual signals include posture, gesture and
facial expression; in fact the whole body,
particularly the tail, conveys information. A
dominant male macaque is instantly recognizable
by his confident walk and by the position of his
tail which is held upright in an emphatic
S-bend; a low-ranking male walks rather
furtively with legs bent, his tail carried
low.
-
- With so many means of expression at their
disposal, anthropoids can communicate very fine
shades of feeling. A dominant male macaque, for
instance, uses a graded series of threat
gestures to control his subordinates. First he
stares directly at the subordinate; then he
opens his mouth (possibly suggesting an
intention to bite); then he bobs his head and
slaps the ground, while uttering coughing
grunts. Finally he lunges at the offender and
attacks him. At any stage in the above sequence
of events the subordinate can, by making an
appeasement gesture, terminate the episode
peacefully. The appropriate gesture in many Old
World primates consists of the subordinate
turning and presenting the hindquarters to the
dominant animal who may briefly mount. These
ritualized gestures, which reduce tension and
prevent fighting, are similar to and possibly
derived from the mating postures of male and
female.
-
- One further visual signal available to
mammals is erection of the hair (pilo-erection).
This is well displayed in the titi of South
America which shows hostility in territorial
defence by fluffing up its fur, arching its back
and swinging its tail from side to side, all of
which makes it look much larger and more
aggressive. The remnants of this ability in man
were recognized by Shakespeare as a response to
extreme fear which, he noted, causes 'each
particular hair to stand on end like quills upon
the fretful porpentine.'
-
- Interpreting the facial expressions of
monkeys and apes is not easy. It is not feasible
to apply simple concepts such as 'aggression'
and 'fear' to the expressions of animals whose
feelings can only be surmised. In many cases
facial expressions appear to be equivocal. For
instance, the retraction of the scalp which
reveals the pale eyelids is sometimes used by a
dominant animal in threat but also by submissive
animals when they are being threatened. The
'lipflip' of the gelada, in which the whole
upper lip is everted, is equally difficult to
interpret. It is performed by both parties when
a male is 'herding' a straying female.
Yawning in adult male baboons reveals the
long dagger-like canines, and could well be
considered a threat, but it may be due to
tension in a situation where the animal is
uncertain how to react; it may even be a genuine
yawn.
-
- An invitation to approach is conveyed to
another monkey by lip-smacking, the rapid
opening and closing of the mouth, sometimes
accompanied by rhythmic tongue protrusion. This
is seen as a prelude to copulation in marmosets
and howlers and in the Sulawesi black
'ape'.
-
- The'play face'is common in primates, and
consists of a widely open niouth, usually with
the upper teeth covered and the lower teeth
exposed. The animal soliciting play looks (but
does not stare or glare) at another individual
and approaches it with exaggerated body
movements, sometimes pouncing on it and
pretending to bite. Like the yawn, the
open mouth can have two meanings, depending on
its context: in play it is a relaxed lively
expression whereas in aggressive interactions it
is tense and threatening.
 - Auditory signals
-
- These are important in the forest where
foliage blocks visual cues. Diurnal forest
dwellers have a large repertoire of calls which
convey information about age sex and social role
just as surely as the olfactory signals of
prosimians. As the facial skeleton and larynx
develop during growth, so the pitch and
resonance of the voice alters. The 'great call'
of the adult female gibbon cannot be imitated by
a juvenile, neither can the deep roar of adult
male howlers which once terrified explorers of
the New World who mistook it for the growling of
jaguars. The characteristic loud call
('whoop-gobble') of the adult male mangabey,
Cercocebiis albigena, is produced for the first
time at about six or seven years of age, a
phenomenon comparable with the breaking of the
voice in human males, and similarly indicating
the attainment of sexual maturity. Many male
and, female 'monogamous' primates (e.g. gibbons,
tarsiers and titis) combine their different
calls in a duet which is usually associated with
territorial defence. The fluent performance of
the duet indicates long practice and thus the
presence of a stable mated pair.
-
- These are all 'spacing' signals, locating a
group in the forest for the information of other
groups. Within a group, members keep in touch by
means of 'contact' calls: black-capped capuchins
in the Colombian rain forest give a low soft
whistle which carries a short distance, and a
strong high-pitched whistle to contact members
who may be as much as 200 metres away.
-
- Most arboreal primates give a distinctive
warning call in the presence of raptorial birds,
enabling the rest of the group to seek shelter
in the lower strata of the forest. The partly
ground-living and partly treeliving vervet
monkey of Kenya has gone one further. It has
evolved the ability to give different alarrn
calls for several different types of predator -
leopard, eagle, snake and baboon. These signals
elicit appropriate responses from other group
members: for instance the eagle alarm call
causes vervets immediately to look upwards and
run into cover; the snake alarm call makes them
look clown on the ground around them, and the
leopard alarm makes them run up a tree or, if
they are already in a tree, climb higher. In
giving the various calls, adults show very
accurate identification, readily distinguishing
the dangerous martial eagle from less deadly
types of predatory bird. Infants are less able
to discriminate and give eagle alarrn calls for
a variety of birds from vultures to pigeons -
even for a falling leaf.
-
- Grooming
-
- Finally the sense of touch is used in
communication by most primates and takes the
form of mutual, or reciprocal, grooming. This
activity consists of one partner approaching
another and presenting a particular part of its
body. The other partner responds by grooming the
fur, parting it to examine the underlying skin
and picking off flakes of dry skin, dust, dirt
or parasites. Each area of skin is carefully and
systematically cleaned, and particular attention
is paid to the face shoulders and back, and to
scratches and wounds. Then roles are exchanged:
groomer becomes groomee and another session
begins. Judging by the intent expression and
persistence of the groomer, the act of grooming
is an absorbing task, and from the total
relaxation and abandon of the groomee, being
groomed is a most soothing experience. What
probably originated as a purely hygienic
exercise, has become in monkeys and apes a
valuable social bond.
-
- Grooming the fur is as important in mammals
as preening in birds. Prosimians Lise the dental
comb and toilet claw for self-grooming. A lemur
scratches itself like a dog and washes itself
like a cat; furthermore the lemur's dental comb
acts as a substitute for the combing action of
the cats rough tongue. In mutual grooming, a
lemur does not use its hands except to grasp its
partner by the head or ears to hold it still
while it licks the fur, using the dental comb to
free any matted hairs. From time to time the
sublingua is used to clear the comb of any
accumulated hairs which are swallowed. It is
significant that prosimians, the primates with
the least dextrous hands, have evolved two
supplementary aids - the toothcomb and the
toilet claw - to help them in the essential task
of keeping the fur clean and comfortable.
-
- Some form of grooming is seen in all
anthropoids, though there are variations in the
amount of time devoted to it. In chimpanzees,
grooming sessions last for hours and undoubtedly
do more than keep the coat clean, important
though this is. Grooming unites mothers and
their offspring in regular grooming parties,
thus strengthening family ties. It allows young
animals to approach adults in a relaxed
atmosphere. It communicates feelings of
relaxation, amity and well-being, and is a vital
link in the cohesion of the group.
-
- Another form of tactile communication
adopted by the douroucouli and titi of South
America is tailtwining. Two or more animals
sleep bunched on a branch with their tails
entwined, demonstrating the mutual attachment of
these family groups.
-
- Chimpanzees seem to approach closely to man
in their gestures of greeting and reassurance in
which the sense of touch is dominant. When
chimpanzees meet after a separation, as often
happens in their informal type of social
organization, they may embrace, hug, kiss, hold
hands, touch or pat each other, depending upon
the degree of friendship between thein. In
moments of sudden alarm, a chimpanzee will reach
out to touch another, deriving reassurance from
the contact. These gestures are so like those of
humans that it is impossible not to accept them
as the counterparts of the human gestures they
resemble .
- Pandiculation:
the comparative phenomenon of systematic
stretching AF Fraser
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