Dolphins whistle for a share of the catch
Dolphins that regularly interact with humans have developed a distinctive whistle to identify their specialist role within the pod, researchers have found.
The discovery was made following observations of dolphin behaviour in the town of Laguna, in the southern Brazilian state of Santa Catarina. Since the mid-19th century, the town’s pristine shallow waters have been the setting for a remarkable example of cooperation between humans and wild animals.
For several weeks every autumn, fishermen can be seen standing in knee-deep water, close to the beach, nets in hand. They are waiting for a group of bottlenose dolphins, 200 metres out to sea, to chase mullet fish towards the shore.
When a shoal approaches, the dolphins give a clear signal – an abrupt dive or tail slap. At that precise moment, the fishermen cast their nets.
Without the help of the dolphins, the humans would never see the approaching fish. The perk for the dolphins is an easy catch: individual fish flee the nets and head straight for their mouths.
The fishermen have long noticed that only a small element of the local dolphin population participates in the joint hunt, and even have names for those individuals who co-operate. Now a team of marine biologists from the Federal University of Santa Catarina has found that these dolphins also emit a notably different whistle, featuring fewer rising notes.
Mauricio Cantor, the lead scientist behind the research, told New Scientist magazine that the variation was most probably a way for the dolphins to identify themselves as members of a particular group within their pod.
‘‘It is as if they speak the same language but use some ‘expressions’ that are exclusive to their social community,’’ he said.
Dolphin societies are known to be complex, with specific ‘‘networks’’ within families fulfilling different tasks. The variation in language is perhaps a way of indicating who does what.
The scientists believe the cooperative trait, and the distinct dialect, is passed from generation to generation as mother dolphins pass the knowledge by example to their calves.