Call of the Wild
Tarzan is best remembered as the man swinging on vines through the jungle, letting out a wild yell as he swoops from tree to tree. Tarzan was a fictional character, but his jungle hollering actually has some basis in reality.
A group of scientists working in Indonesia followed several orangutans through the jungle, focusing attention on flanged males--the dominant fellows with the big cheek pads who emit spontaneous long calls at various points each day.
The researchers recorded detailed information about the animals' travel routes, and also their vocal activity. By comparing the direction each orangutan faced when making a long call to the direction he ended up travelling next, the scientists discovered the purpose of all that hollering: the orangutans were letting their neighbors know their plans.
Female orangutans like to keep in earshot of the most macho males in the area, to seek them out as mates. Subordinate males, on the other hand, like to steer clear. Everyone listens for the long calls to find out where the big dudes are headed, and adjust their own routes accordingly. The last long call of the evening is especially telling: It indicates the flanged male's plans for the next day.
This discovery is exciting because it indicates, for the first time, that orangutans in the wild are capable of longterm planning. Plus, I guess it shows that just like Tarzan, they want to get Jane's attention.
"Wild Orangutan Males Plan and Communication Their Travel Direction One Day in Advance" (PLOS ONE)