E. D Starm 
against females from outside their sub- 
group and will even defend each other’s 
young. Other females, however, rarely 
interact. When subgroups of female as- 
sociates form, they tend to use the same 
area of the range continually, and these 
favorite areas tend to be in overlapping 
troop zones. Close associations and the 
use of favorite areas may occur because 
all females transfer out of their natal 
troop. When females that are age-mates 
and thus not sisters (or at least do not 
have the same mother, although they 
may have the same father) transfer into 
the same troop, they tend to spend the 
majority of their time together. When 
these females wander off as part of a 
subgroup, they tend to go to areas 
where their present troop range over- 
laps with their natal troop’s range. Why 
they return to these areas is not clear. 
They do not interact peacefully with 
any of their previous troop mates. In 
fact, they either ignore, threaten, or flee 
from individuals they once associated 
with peacefully. They may be monitor- 
ing the resource situation and social 
setting for a possible return. It is not yet 
clear whether females ever return to 
their natal troop for an extended peri- 
od. Certainly some females transfer 
more than'once. One subadult female 
joined the study troop during estrus, 
transferred to a neighboring troop for 
the birth of her son, and then returned 
to the study troop with her month-old 
offspring. Another adult female accom- 
panied her prepubescent, subadult 
An adult female red colobus 
grooms an adult male green vervet, 
above. Such grooming bouts are 
a frequent sight in The Gambia's 
Abuko Nature Reserve, where the 
vervets are ubiquitous. Red colobus 
males may even join a group of 
vervets while shadowing a colobus 
troop that they want to transfer 
into. Other types of interactions 
between the two species, such as 
the scene at right, are rare. 
daughter to a neighboring troop, stayed 
with her for a week, and then returned 
to the study troop. 
Females transfer voluntarily and 
successfully. They do not spend time as 
solitaries shadowing other colobus 
troops; rather, they tend to transfer 
during intertroop encounters. A few 
months before transferring, a female’s 
behavior changes. She begins to seek 
out vervets for resting and grooming 
sessions, and eventually she will head 
off in a direction opposite from the 
troop. An adult male usually runs after 
her. The male will not attempt to herd 
her, but will make a number of friendly 
gestures, such as mounting and groom- 
ing. So far, however, I have not seen a 
male successfully entice any young fe- 
male to stay in her natal troop. All of 
the females known to have been born 
into the main study troop have left ei- 
ther before or during their first adoles- 
cent sexual swelling, which occurs 
during their third year. 
When a female transfers, she is ac- 
cepted by the males and the subadult 
and juvenile females in her new troop. 
She will usually be chased and receive 
threats from some of the resident adult 
females. These differing reactions are to 
be expected since the female will be a 
potential mate for the males and a po- 
tential competitor for resources with 
the other females. Because juvenile and 
subadult females will soon be leaving 
the troop, they will gain if the new fe- 
male stays in their natal troop, instead 
of transferring again, possibly to be- 
come a potential competitor in their 
new troop. Although all females leave 
their natal troop, they are replaced by 
40 
