Male dolphins boost their social lives by whistling to each other at a distance, according to new research.

The high pitched sound tells others they are present and wish to make contact. It helps the marine mammals maintain key community ties, say scientists, describing the rarest type of social organization in the animal kingdom.

And, now, reports Science.org, researchers report this male bonding has a big evolutionary payoff: Dolphins with the strongest buddy bonds actually father more offspring.

Comparing genetic data collected from these males, an evolutionary biologist at the University of New South Wales, Sydney, determined that males who had the strongest social bonds and were friends with all members of their alliance had the most offspring.

Lead author Emma Chereskin of the University of Bristol says, "By forming strong alliances with others, males can influence their own reproductive success in a way that wouldn't be possible as single individuals."

"As the number of close social relationships increases, so too do the demands on the time and space available for relationship maintenance through physical contact."

"We wanted to know how they maintained multiple alliance relationships in large groups."

Language evolved to support long-distance social bonding. They are also known to use physical contact, such as gentle petting, to connect with strongly-bonded friends.

The international team analyzed nine years of data from a dolphin population in Shark Bay, Western Australia. The findings published in Current Biology, shed fresh light on how they reinforced and maintained valuable alliances-which can endure for decades

Ms. Chereskin and colleague tracked groups of affiliated males, documenting their physical and acoustic behavior. It enabled them to identify the different ways they bonded with each other and formed concepts of ‘team membership'.

Senior author Dr Stephanie King, also from Bristol, said, "We found within the core dolphin alliances, strongly bonded allies engaged in more affiliative contact behavior, such as petting and rubbing, while weakly bonded allies engaged in more whistle exchanges.

"This illustrates these weaker, but still key, social relationships can be maintained with vocal exchanges."

"Our findings provide new evidence that vocal exchanges can serve a bonding function," says Chereskin.

"But more importantly, vocal exchanges can function as a replacement of physical bonding, allowing allied male dolphins to ‘bond-at-a-distance'.

Inhabiting seas worldwide, bottlenose dolphins are renowned for their intelligence and mimicry. In some areas, they also cooperate with local fishermen by driving fish into their nets and eating the fish that escape.

They have sharp eyesight but use echolocation to explore and search out prey when visibility is limited. And they also communicate through pulsed sounds, clicks, and body language.

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