colobus offspring can get along without 
milk. One female was orphaned when 
she was nine months old, and while she 
did not need her mother’s milk, she 
probably did need a protector. Her old- 
er sister adopted her and was extremely 
possessive and protective toward her, 
much more so than any mother would 
be. This restrictive “sistering” probably 
reduced the chances of falls, kidnap- 
ping, and predation, but it also prob- 
ably contributed to the orphan’s ob- 
viously slow social development.) 
The continual separating and reunit- 
ing of troop members takes place 
throughout the year, probably for a va- 
riety of reasons. The fluidity of the 
troop allows each member to move 
freely and thus avoid aggressive inter- 
actions. During the mating season 
there is much helter-skelter movement; 
boisterous, highly visible nondirection- 
al displays by estrous females are fre- 
quent; and intermittent, aggressive 
intertroop encounters and male-male 
harassment take place. During this pe- 
riod it is not uncommon for old females 
and pregnant and lactating females 
with their dependent offspring to ab- 
sent themselves from the males and es- 
trous females. Such females and their 
young would have little to gain by get- 
ting involved in intertroop encounters 
at this time. 
Fusion-fission is more apparent dur- 
ing the mating season, but because it 
also occurs during the rest of the year, it 
can be viewed as a response to the den- 
sity and dispersion of resources. When 
a major food source is heavily clumped 
and can support many feeders, the en- 
tire troop will frequently feed together. 
When the major food source is widely 
dispersed or when there are many ma- 
jor food sources available at the same 
time, the feeders tend to break up into 
various subgroups throughout the 
range, thereby minimizing competition 
and maximizing the amount of range 
monitored. Because they are spread 
over a larger space, the colobus see 
more of the range and possibly learn 
about the availability of food sooner. 
While the size and composition of 
each subgroup is not stable and endless 
combinations of individuals occur, 
there are some common patterns. 
Members of the same subgroup tend to 
be close associates. Some females have 
very close relationships with each oth- 
er. They groom frequently, huddle to- 
gether, and their offspring are 
playmates. They will defend each other 
39 
