Researchers have made a breakthrough in understanding the complex social structures of Shark Bay’s dolphins, observing the male mammals using individual call signs, or names, to help recognise both their friends and enemies.
The discovery, made by scientists from the University of Western Australia, is helping to explain the intricate networks among the dolphin population at the popular world heritage site.
Male dolphins are known to form small alliances of two or three to work together to find females to mate with.
But UWA researcher Stephanie King said the Shark Bay dolphins had even more complex structures.
Pairs and trios of dolphins joined together to form larger alliances of 10-14 to help each other defend females from competing alliances or to steal females from those other groupings.
Telling friend from foe
Dr King said while that was already known, researchers were interested in how those male dolphins were able to identify each other and work out who was a friend or foe.
She said typically animals with vocal ability had individual call signs until they joined a group, when this changed and they produced a shared alliance signal or vocal “badge” to link each other together.
“Intriguingly we found out that wasn’t the case in Shark Bay,” Dr King said.
“Males retain their own individual vocal label or name, and do not make their calls more similar.
“So each male in their lives [has] a very different whistle or vocal label, and they can use this to track relationships.
So they identify their friends, their rivals, the friends of their rivals, and it allows them to build this really complicated network of alliance formation.”
It also allowed them to track the history of their relationships.
“Who have I cooperated with, who do I want to cooperate with again, who am I competing with,” Dr King said.
“And this is very unusual in the animal kingdom because most animals when they form strong bonds, they will converge, they will have a group call.”
But the Shark Bay dolphins are not alone in retaining individual call signs, according to Gisela Kaplan, professor in animal behaviour at New England University.
She said song birds and parrots could do the same, even when they belonged to large groupings. There was some overlap in their signals, but also difference.
“They do everything together, yet they do have individual calls as well,” Professor Kaplan said.
Cooperation is key
But the questions remains: why are Shark Bay’s dolphins different in this respect to other dolphins and so many other animal species? Why the need for such complex social structures?
Dr King theorised it could have to do with the very high density of dolphins there, and the higher number of males than females.
By working together, she said, the males had a higher chance of getting access to the females than if they worked alone.
“So here cooperation is the key,” she said.
“You have to work with your male partners in order to get access to those females, just because of how high the density is in that population.”
Male dolphins have a greater chance of success with females if they work together. (Supplied: Simon J Allen, The Dolphin Alliance Project)
The researchers also found that since the dolphins did not share a call sign, they used other means to strengthen relationships.
“They’ll rub each others pectoral fins against one another [as a form of] affiliative contact,” Dr King pointed out.
“Similar to holding hands or hugging in humans, where you do that with people you have a close relationship with, perhaps it makes you feel better. But the males engage in this kind of behaviour as a way of strengthening their social bonds.”