As they grow older, male chimpanzees follow along with adult males patrolling the periphery
of the community. Members of the patrol look for members of another community that strayed into their area. They move
cautiously across the ground in a tight group formation. The ground, leaves, and tree trunks are sniffed for signs of a
stranger. They stop frequently to climb tall trees, gaze, listen, and look over the area of a neighboring group. The
chance discovery of a fresh night nest causes alarm. The nest is destroyed while making intimidating gestural, vocal,
and postural displays. If a stranger is not encountered the patrol party returns to its home territory. If the patrol
runs into strangers, with roughly equal numbers of males, a vigorous display with vocal threats such as pant-hooting,
roaring pant-hoots, and waa-barks ensues. Most of the time, after making a lot of noise, one party will retreat to
their core area. If the patrol encounters a stranger, aggression may occur.
November 1974 The three Kahama males Charlie, Sniff, and Willy Wally have captured a piglet.
As they feed, another adult male appears on the far side of a narrow ravine. The observer has never seen him before; he
is obviously a member of the powerful Kalande community that ranges over the hills to the south. Charlie, upon seeing the
stranger, drops his meat and runs northward, closely followed by Sniff and Willy Wally. The observer hastens after them
and presently finds Charlie in a tree, screaming loudly. Other chimpanzees are calling up ahead, so the observer leaves
Charlie and runs on. A few minutes later he catches up with Sniff. Hair bristling, the young male is performing a spectacular
display along a trail parkway down a steep-sided ravine. Charlie is still screaming back in the forest, but Sniff is uttering
deep, fierce-sounding roar pant-hoots. Below, hidden in the vegetation, other chimpanzees are heard calling loudly and
charging through the undergrowth. Sniff, as he displays, repeatedly picks up large rocks and hurls them into the ravine
so that they land near the strangers beneath. He hurls at least thirteen before he moves out of sight. The chimpanzees
below are throwing too; every so often a rock or stick flies up from the undergrowth but, falling far short of Sniff,
the missiles roll back harmlessly into the ravine. The observer determines that at least three of the strangers are adult
males. They see him and retreat southwards.
Source: Patterns of Behavior, Chapter 17, Introduction.