thanks @kevinwong!
Ooo patrols are awesome. Chimpanzees are territorial and sometimes part of a group will walk along the borders of their range. Unlike usual, they get all quiet, listening carefully for signs of neighboring groups. If they come across a member of another group, they'll sometimes attack. Instances of chimpanzee violence more often occur around patrols. The reasons they do this aren't entirely clear, but it seems they might be able to a) gain new territory to increase resources, b) improve their safety by deterring the other groups from infringing on territory, c) recruiting new females into their community.
Reveal spoiler
Image by John Mitani
For more, you can check out this video or articles like this one, Mitani & Watts 2004