From wiki
Under ideal conditions, the sound can be understood at 3 to 7 miles,[1] but interesting messages usually get relayed on by the next village. "The talking drums" or "jungle drums" is also a euphemism for gossip – similar to "the grapevine".
n Africa, New Guinea and the tropical America, people have used drum telegraphy to communicate with each other from far away for centuries. When European expeditions came into the jungles to explore the primeval forest, they were surprised to find that the message of their coming and their intention was carried through the woods a step in advance of their arrival. An African message can be transmitted at the speed of 100 miles in an hour.
full link http://en.wikipedia.org/wiki/Drums_in_communication