One by one, the others respond, their voices overlapping in a sonorous, infrasonic chorus that whispers across the savanna. This elephant barbershop quartet conveys a clear message: It's time to move on. Gradually, the elephants shift, their massive bodies swaying as they follow their rumbling leader to the next stop on their nocturnal wanderings. For the first time, scientists from Stanford University and other institutions have documented male elephants using "let's go" rumbles to signal the start of group departures from the Mushara waterhole in Etosha National Park, Namibia. The vocalizations are initiated by the most socially integrated, and often the most dominant, males in closeknit social groups.