World Wildlife Fund. M Bijleveld 
E 0 Stann 
threaten and give chase to strange 
males, strange males have not been ob- 
served threatening and chasing resident 
females. In fact, one strange adult male, 
while being chased off by the local 
troop, gave frantic appeasement ges- 
tures to a resident adult female that ig- 
nored him. 
I did witness one successful male 
transfer. A young subadult male spent 
more than a year as a member of a ver- 
vet troop, shadowing both the study 
troop and a neighboring troop. After 
one of the two resident males in the 
neighboring troop disappeared, this 
young male successfully joined the 
troop and has now been resident for one 
year. There is also a very old adult male 
now living on the periphery of the local 
troop’s range. While he occasionally 
meets up with an exiled thirty-two- 
month-old male from the local troop, 
he spends most of his time alone, mov- 
ing slowly on the forest floor, avoiding 
all contact with mixed groups. 
The methods and results of transfer- 
ring show clear sexual differences. This 
suggests that the troop has very differ- 
ent meanings for females and males. A 
colobus female probably views a troop 
as an open unit that she can easily in- 
vestigate and, if she chooses, can join. If 
she decides that another troop would be 
better, she switches. The decision as to 
what troop she will join appears to be 
entirely up to her. Her allegiance to her 
present troop is intense, but she is liable 
to make a quick switch. This may be 
why males rarely display aggressive be- 
haviors toward females, for there is al- 
ways the possibility that if life gets too 
rough, a female will simply pick up and 
leave. Certainly, males do not normally 
dominate females, and it is often appar- 
ent that males go out of their way to en- 
gage females in friendly behaviors. 
A nonresident colobus male prob- 
ably sees a troop as a fairly closed unit, 
which he can only investigate from afar 
and cannot easily join. The decision as 
to whether he will join a troop is not up 
to him alone. Rather, it is a decision 
probably made by the resident troop 
members. If he is able to stay in his na- 
tal troop or make a successful transfer, 
his allegiance, like that of the females, is 
also intense. Once in a troop, he will use 
all his persuasive powers to try to get as 
many females as possible to remain 
with him. 
In the literature, there are frequent 
statements that transfers between 
troops occur in order to eliminate the 
possible deleterious effects of inbreed- 
ing. If this were the only reason for 
transferring, then only one of the sexes 
would have to relocate. Both sexes 
leave the natal troop, however, so it 
must occur for another reason or, more 
likely, a number of reasons. 
Clive Marsh, who studied the Tana 
River red colobus in Kenya, has sug- 
gested that the function of female trans- 
ference may be related to mate choice 
and the avoidance of infanticide. This 
suggestion appears to hold true for the 
Pools and swamps in the Abuko 
reserve, left, are inhabited by 
Nile crocodiles, predators of 
western red colobus. The young 
pregnant colobus, right, 
is engaging in a grooming bout 
with a 3'/ 2 -year-oId male. 
Abuko red colobus population. Many 
of the more interesting behaviors — the 
killing of intruder males, particularly 
by adult females; the ease with which 
females can investigate troops; the diffi- 
culty males have in gaining access to 
troops; the chasing off of strange males 
by females; and the rarity of aggression 
displayed by resident adult males to- 
ward females and their offspring — may 
also be related to choosing mates that 
are not potentially infanticidal. It may 
not be mere coincidence that both ob- 
served attacks were led by females, that 
no mother with dependent offspring 
was seen anywhere near an intruder 
male, and that all partly weaned young 
ran off and quietly hid for the duration 
of the attacks. Females may well be able 
to judge which males will be promising 
mates and which are potentially infan- 
ticidal, and act accordingly. 
Although we now know that red co- 
lobus display a form of fusion-fission 
organization, that females voluntarily 
leave their natal troop, that males are 
usually expelled, that females transfer 
easily and successfully between troops, 
that males encounter more difficulties 
in joining a new troop, and that intrud- 
er males are sometimes killed, the colo- 
bus puzzle is still partly scrambled. Do 
grandmothers ever meet their grand- 
children? Does a younger sister join the 
same troop as her older sisters? Does 
the mother’s behavior determine 
whether her son will remain in the 
troop or leave? Do expelled juvenile 
males return to their natal troops when 
they reach adulthood? Is female friend- 
ship based solely on a common natal 
troop experience? How closely related 
are female associates? Why are some in- 
truder males killed and others accept- 
ed? What is a female investigating when 
she enters a new troop? Why do some 
females transfer over and over again 
and others perhaps only once? In light 
of the current interest in reproductive 
strategies, male and female behaviors, 
and kinship theories, the red colobus 
are very intriguing and appropriate ani- 
mals to study. 
42 
