When it comes to making friends, it appears dolphins are just like us and form close friendships with other dolphins that have a common interest, according to new research led by The University of Western Australia.
The findings, published in the Proceedings of the Royal Society B by an international team of researchers from the Universities of Zurich, Bristol and Western Australia, provides further insight into the social habits of these remarkable animals.
Shark Bay, a World Heritage area in Western Australia, is home to an iconic population of Indo-Pacific bottlenose dolphins, and the only place where dolphins have been observed using marine sponges as foraging tools.
Study co-author Dr Simon Allen, an adjunct research fellow with UWA's School of Biological Sciences and senior research associate at Bristol's School of Biological Sciences, said the learnt technique, passed down from generation to generation, helped certain dolphins known as "spongers" find food in deeper water channels.
"While the tool-using technique is well-studied in female dolphins, this study looked specifically at male dolphins," Dr Allen said.
Using behavioural, genetic and photographic data collected from 124 male dolphins during the winter months in Shark Bay over nine years from 2007 to 2015, the team analysed a subset of 37 male dolphins, comprising 13 spongers and 24 non-spongers.
Dr Allen said male spongers spent more time associating with other male spongers than they did non-spongers, these bonds being based on similar foraging techniques and not relatedness or other factors.
"Foraging with a sponge is a time-consuming and largely solitary activity so it was long thought incompatible with the needs of male dolphins in Shark Bay - to invest time in forming close alliances with other males," he said.
"This study suggests that, like their female counterparts and indeed like humans, male dolphins form social bonds based on shared interests."
The study provides new insight into friendship-making behaviour in the social network of tool-using dolphins.
Manuela Bizzozzero, lead author of the study at the University of Zurich said male dolphins in Shark Bay exhibited a fascinating social system of nested alliance formation.
"These strong bonds between males can last for decades and are critical to each male's mating success," Ms Bizzozzero said. "We were very excited to discover alliances of spongers, dolphins forming close friendships with others with similar traits."
The study was funded by grants from the Swiss National Science Foundation, National Geographic Society, Australia's Sea World Research and Rescue Foundation Inc (SWRRFI), WV Scott Foundation and the AH Schultz Stiftung.
