80 CHAPTER 4 | Primate Behavior
of food. Ranges often change seasonally, and the number
of miles traveled by a group in a day varies. Some areas,
known as core areas, are used more often than others.
Core areas typically contain water, food sources, resting
places, and sleeping trees. The ranges of different groups
may overlap, as among bonobos, where 65 percent of one
community’s range may overlap with that of another.^4 By
contrast, chimpanzee territories, at least in some regions,
are exclusively occupied and will be defended from intru-
sion (Figure 4.1).
Gorillas do not defend their home range against
incursions of others of their kind, although they will
defend their group if it is in any way threatened. In the
lowlands of Central Africa, it is not uncommon to find
several families feeding in close proximity to one an-
other.^5 In encounters with other communities, bonobos
will defend their immediate space through vocaliza-
tions and displays but rarely through fighting. Usually,
they settle down and feed side by side, not infrequently
grooming, playing, and engaging in sexual activity be-
tween groups as well.
Chimpanzees, by contrast, have been observed pa-
trolling their territories to ward off potential trespassers.
Moreover, Jane Goodall (see Anthropologists of Note)
has recorded the destruction of one chimpanzee commu-
nity by another invading group. This sort of deadly inter-
community interaction has never been observed among
bonobos. Some have interpreted the apparent territorial
behavior as an expression of the supposedly violent na-
ture of chimpanzees. However, another interpretation is
that the violence that Goodall witnessed was a response to
crowding as a consequence of human activity.^6The gorilla group is a “family” of five to thirty indi-
viduals led by a mature silver-backed male and including
younger (black-backed) males, females, the young, and
occasionally other silverbacks. Subordinate males, however,
are usually prevented by the dominant male from mat-
ing with the group’s females. Thus young, sexually mature
males, who take on the characteristic silver color at the end
of the sexual maturation process (about 11 to 13 years of
age), are forced to leave their natal group—the community
they have known since birth—by the dominant silverback.
After some time as a solitary male in the forest, a young
silverback may find the opportunity to start his own social
group by winning outside females. In the natal group, if
the dominant male is weakening with age, one of his sons
may remain with the group to succeed to his father’s po-
sition. Alternatively, an outside male may take over the
group. With the dominant male controlling the group, go-
rillas rarely fight over food, territory, or sex, but they will
fight fiercely to maintain the integrity of the group.
In many primate species, including humans, adolescence
is a time during which individuals change the relationships
they have had with their natal group. Among primates this
change takes the form of migration to new social groups. In
many species, females constitute the core of the social system.
For example, offspring tend to remain with the group to
which their mother, rather than their father, belongs. Among
gorillas, male adolescents leave their natal groups more
frequently than females. However, adolescent female chim-
panzees and bonobos are frequently the ones to migrate.
In two Tanzanian chimpanzee communities studied,
about half the females may leave the community they have
known since birth to join another group.^3 Other females
may also temporarily leave their group to mate with males
of another group. Among bonobos, adolescent females
appear to always transfer to another group, where they
promptly establish bonds with females of their new group.
While biological factors such as the hormonal influences
on sexual maturity play a role in adolescent migration,
the variation across species, and within the chimpanzees
in dispersal patterns, indicates that differences may also
derive from the learned social traditions of the group.
Home Range
Primates usually move about within a circumscribed
area, or home range, which varies in size depending on
the group and on ecological factors such as availability
natal group The group or the community an animal has in-
habited since birth.
home range The geographic area within which a group of
primates usually moves.(^3) Moore, J. (1998). Comment. Current Anthropology 39, 412.
Figure 4.1 Home ranges illustrated in A can be overlapping.
When members of the same species meet one another in
the shared parts of the range, there might be some tension,
deference, or peaceful mingling. Some groups maintain clear
territories (B) that are strictly defended from any intrusion by
members of the same species.
(^4) Parish, A. R. (1998). Comment. Current Anthropology 39 , 414.
(^5) Parnell, R. (1999). Gorilla exposé. Natural History 108 (8), 43.
(^6) Power, M. G. (1995). Gombe revisited: Are chimpanzees violent and
hierarchical in the “free” state? General Anthropology 2 (1), 5–9.
A B