E D Starm 
chimpanzees, South American spider 
monkeys, and hamadryas baboons, co- 
lobus troop members form subgroups 
that separate and coalesce. Moreover, it 
soon became apparent that all females 
and most males leave their natal troop, 
that the two sexes display very different 
behaviors when transferring between 
troops, and that males attempting to 
enter a new troop are sometimes killed. 
While female transfer may be unusu- 
al for nonhuman primates — only goril- 
la and chimpanzee females are known 
to regularly transfer between social 
units — it may be a general red colobus 
trait. Researchers studying red colobus 
in the Kibale rain forest in Uganda and 
in the gallery forest along the lower 
Tana River in Kenya also found that fe- 
males are the most mobile individuals. 
It is not yet clear, however, whether the 
continual separating and coalescing of 
individuals and the killing of intruder 
males are species-specific traits or ad- 
aptations to the specific ecological, de- 
mographic, and social conditions of 
Abuko. 
Most red colobus in the Abuko re- 
serve live in mixed social units, called 
troops, of about twenty-three individ- 
uals. At present, my main study troop 
has nine adult females, two adult males, 
seven subadults and juveniles, and five 
newborn infants. The surrounding 
troops, whose home ranges overlap ex- 
tensively with that of the main study 
troop, show similar compositions. 
Each troop consists of individuals 
A female pauses with her twenty-day- 
old infant, above, which will be 
weaned when it is roughly nine 
months old. The group of colobus 
resting calmly on the branch of 
a tree, right, includes an adult 
male (center) and an adult female 
(right). The female's two-year- 
old daughter (left) will transfer 
out of her natal troop just 
before or during her first estrus, 
which will occur when she is three. 
that associate together frequently and 
peacefully and share a common home 
range. Older individuals take prece- 
dence over younger ones, and mothers 
will defend their young, but aggressive 
interactions between resident troop 
members are infrequent. What intra- 
troop conflict occurs generally takes 
the form of facial and vocal threats and 
rarely entails fighting. Frequently, a 
threatening facial expression is quickly 
transformed into an appeasement ex- 
pression and a grooming bout ensues. 
Because of the rarity of agonistic inter- 
actions, the frequency of friendly be- 
haviors, and a weakly defined adult- 
dominance hierarchy in which the 
resident males and females actively co- 
operate to repel some intruder males, it 
appears that dominance-subordinance 
relationships are not too important in 
maintaining harmony within the troop. 
Troop members frequently separate 
and reunite. Sometimes up to three sep- 
arate groups are formed, and these sub- 
groups can remain apart for days at a 
time. The colobus pattern differs from 
the observed fusion-fission of chimpan- 
zees, hamadryas baboons, and spider 
monkeys in that colobus spend more 
time together as a troop, and resident 
adult males seldom wander off alone or 
in a group. Resident adult males in 
their prime are normally with at least 
one female. Resident colobus females, 
however, have been observed to wander 
off alone. And old adults of both sexes 
wander off alone before they die. Be- 
cause of this fusion-fission, mothers can 
be observed in different subgroups from 
their unweaned offspring for days at a 
time. (After they are nine months old, 
38 
