Bottlenose dolphins that have learned to use sea sponges as hunting tools form cliques with others that do the same — the first evidence of animal grouping based on mutual interest, according to a new study. The finding may represent the first known proof of cultural behavior in the animal kingdom, the researchers wrote.

They studied a group of bottlenose dolphins at Australia’s Shark Bay, some of whom had learnt the skill of “sponging” — slipping a sponge on their beaks as protection against sharp rocks while scouring the ocean floor for prey. Based on 22 years of observations, the team found that the “spongers” forged closer ties with other spongers than with dolphins that had not acquired the hunting technique. They published their work, which forms part of an ongoing scientific quest for proof of animal culture — loosely defined as a form of social learning that differentiates between groups – in Nature Communications.