One of chimps' most common sounds is the "pant-hoot."
"The pant-hoot means something like 'Hey! This is me! I'm here!,'" said Michael Wilson, lead author of the study. "It's a way to keep track of allies and associates."
Wilson, director of field research at Goodall's Gombe Stream Research Centre in Tanzania, added, "People studying chimpanzees use a rather similar call to find one another in the dense forest — a sort of loud 'hoo' that can be heard over a few hundred yards.
"When you're looking for someone in the forest, you give a hoo, listen for their response, and move towards them once you've localized their call. Chimpanzees use their pant-hoots in much the same way."
To test the chimps' ability to control these sounds, Wilson and his team recorded a "pant-hoot" from a male chimp. Using a hidden speaker, the scientists played the sound back to other wild chimps that did not belong to the recorded male's social group.
When at least three males heard the stranger, they ganged up around the speaker area and pant-hooted loudly.
"I'm sure they intended to drive off the intruder," Wilson told Discovery News. "And the sound of a big group of male chimpanzees calling in response to a stranger is a pretty scary sound!"
When only one or two males were present to hear the recording, they remained quiet, perhaps observing they may lose a fight with the "intruder." Females quietly approached the speaker area and then fled from the phantom stranger.
