Dolphins form close friendships based on shared common interests, just like humans do, a study claims.
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.
This learnt technique, passed down from generation to generation, helps certain dolphins, "spongers", find food in deeper water channels.
While the tool-using technique is well-studied in female dolphins, the researchers from University of Bristol in the UK and University of Zurich in Switzerland study looked specifically at male dolphins.
Using behavioural, genetic and photographic data collected from 124 male dolphins during the winter months in Shark Bay over nine years (2007 to 2015), the team analysed a subset of 37 male dolphins, comprising 13 spongers and 24 non-spongers.
Male spongers spend more time associating with other male spongers than they do 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," said Simon Allen, a senior research associate at University of Bristol.
"This study suggests that, like their female counterparts and indeed like humans, male dolphins form social bonds based on shared interests," said Allen.
The study provides new insight into homophilous behaviour in the social network of tool-using dolphins.
