The male Indo-Pacific bottlenose dolphins of Australia's Shark Bay are notorious for their gang-like behaviors. Scientist have studied these mammals since the 1980's and their bonding has a payoff: Dolphins with the strongest buddy bond father more offspring. A second study revealed whistling maintains the male dolphin's friendships. Every dolphin has a signature contact whistle they learned from their mother. The caller emits his whistle and the receiver replies with his own whistle. Doing this strengthens their bond, says co-author Stephanie King, a behavioral biologist also at the University of Bristol. It's a low-cost way to maintain these relationships. Male dolphins, the scientists found, whistle to touch partners that were 10 or more meters away and difficult to contact physically.