Playing together as juveniles helps male dolphins become more successful as adults, according to a new study.

The findings, led by researchers from The University of Western Australia and University of Bristol, show that juvenile male dolphins with strong social bonds practise adult-like reproductive behaviour when playing together, and those juvenile males who spend more time practising will father more offspring as adults.

Lead author Dr Katy Holmes said the study, published in Proceedings of the National Academy of Sciences, provided rare evidence for a link between juvenile social play and reproductive success in a wild animal.

In collaboration with international colleagues, the scientists spent years observing the behaviour of juvenile male Indo-Pacific bottlenose dolphins in Shark Bay, Western Australia.

Using long-term behavioural and genetic data from the Shark Bay dolphin population, they investigated the role of juvenile social play in developing adult male reproductive behaviour.

Dr Holmes, who completed the work as part of her doctoral research at The University of Western Australia, said the researchers found that juvenile play involved immature versions of adult reproductive behaviours, which were crucial for males to access and mate with fertile females.

“What we found was that the time the dolphins spent engaged in these play behaviours predicted how many offspring the males would eventually sire as adults,” she said.

Adult male dolphins in Shark Bay form long-term alliances to help each other secure access to females and these alliances are formed between males who closely bonded as juveniles.

As adults, pairs or trios of allied males will coordinate their behaviour to attract individual females, and the new findings show that young males practise this coordination with their likely future allies, years before they become sexually mature.

“Our work is exciting because historically it has been notoriously difficult to link play behaviour to reproductive success, in this case the number of sired offspring, in wild animals,” Dr Holmes said.

Senior author Dr Stephanie King, Associate Professor from Bristol’s School of Biological Sciences said play behaviour was widespread in humans and other animals, but the reasons that animals play together had long remained a mystery.

“This study provides compelling support for the idea that animals in the wild play together to practise behaviours that will be important for them as adults, and that if they practise enough, they will be more successful as adults,” Dr King said.