A new study has revealed that male bottlenose dolphins impress females by carrying pieces of plants and twigs defying earlier beliefs that it is their playful behaviour that does the trick for them.
It is quite rare in the animal kingdom that animals indulge in sexual display through object-carrying, with only humans and chimpanzees doing anything similar.
However, the habit has been observed in isolated populations of dolphins in river dolphins in Brazil, Venezuela and Bolivia suggests it has either been passed on through generations or evolved separately in different groups. This discovery could provide proof of the existence of dolphin culture that is defined as a non-hereditary, complex skill taught to some members of a population by others and passed down through generations.
Until recently, culture was seen as a defining human characteristic not shared by other species. This is why the suggestion that dolphins also exhibit cultural behaviours is controversial. Dr Tony Martin of the British Antarctic Survey in Cambridge, and Dr Vera da Silva, from the National Institute of Amazonian Research in Brazil studied 6,026 groups of dolphins in Mamiraua, a flooded rainforest reserve in Brazil.
Out of these 221 groups, at least one individual was carrying an object such as weed, a stick or a lump of clay. Such groups usually contained adult females, and the carriers were nearly always adult males. Aggression between males was also 40 times more likely in the object-carrying groups.
The scientists said that if the object-carrying was just playfulness, females and juveniles would also have been expected to carry objects, however they did not.
DNA analysis of tissue samples collected from adults and calves was also carried out, which backed up their theory. "I was struck by how many of the most frequent object-carriers were on the list of probable fathers of individual calves," Telegraph quoted Dr. Martin, as saying. He added: "It's so unusual that many of my colleagues were sceptical when I first suggested the idea, but now I think the evidence is overwhelming."
Bottlenose dolphins in Shark Bay, western Australia, break off pieces of marine sponge carrying them on their snouts in order to protect themselves as they probe the ocean floor. It is the only known example of tool use among dolphins, and the scientists who made the discovery also concluded this was evidence of cultural behaviour. "I'm now convinced this behaviour is social learning - and from that point of view, you can call it a culture," said Dr Michael Krutzen, from the University of Zurich in Switzerland.
The findings of the study will be presented at a conference organised by the Society for Marine Mammalogy in Cape Town, South Africa.