Pitch perfect Why whistling means so much to dolphins
MALE dolphins boost their social lives... by whistling at each other, according to new research.
The high-pitched sound tells others they are present – and wish to make contact. It helps the enigmatic marine mammals maintain key community ties, say scientists.
Lead author Emma Chereskin, a student at the University of Bristol, explained: “Many animals, including humans, use tactile contact, touch, to strengthen and reaffirm important relationships.
“But as the number of close social relationships increases, so too do the demands on the time and space available for relationship maintenance through physical contact.
“Male bottlenose dolphins form strategic, multi-level alliances, and we wanted to know how they maintained multiple alliance relationships in large groups.”
They are known to use physical contact such as gentle petting to connect with strongly bonded allies.
The study in the journal Current Biology shows they rely on less timedemanding vocal exchanges to stay connected with the rest.
An international team analysed nine years of data from a dolphin population in Shark Bay, Western Australia.
The findings shed fresh light on how they reinforced and maintained valuable alliances.
Ms Chereskin and colleagues tracked groups of affiliated males – documenting their physical and acoustic behaviour.
It enabled them to identify the different ways they bonded with each other.
Dolphins team up to hunt or protect themselves from predators. They form concepts of ‘team membership.’
Adult male bottlenoses live mostly alone or in groups of two to three and join pods for short periods of time.
These usually number around 10 to 30 members, although ‘superpods’ of more than 1,000 have been recorded.
Senior author Dr Stephanie King, also from Bristol, said: “We found within the core dolphin alliances, strongly bonded allies engaged in more affiliative contact behaviour, such as petting and rubbing, while weakly bonded allies engaged in more whistle exchanges.
“This illustrates these weaker but still key social relationships can be maintained with vocal exchanges.”
It backs British anthropologist Professor Robin Dunbar’s theory that vocalisations and language evolved to replace grooming.
Increasingly, large group sizes placed impossible demands on the time available for physical contact.
Ms Chereskin said: “Our findings provide new evidence that vocal exchanges can serve a bonding function.
“But more importantly, and in line with the social bonding hypothesis, vocal exchanges can function as a replacement of physical bonding, allowing allied male dolphins to bond at a distance.
“This evidence in support of the social bonding hypothesis outside of the primate lineage raises exciting new questions on the origins and evolution of language.”
Bottlenose dolphins inhabit warm and temperate seas worldwide, being found everywhere except around the Arctic and Antarctic.
They are renowned for their intelligence and mimicry. They use marine sponges as tools to reach food that would normally be inaccessible.
Bottlenose dolphins gained popularity from aquarium shows and TV shows such as Flipper.
They have also been trained by militaries to locate sea mines or detect and mark enemy divers.
In some areas, they cooperate with local fishermen by driving fish into their nets and eating the fish that escape.
Dolphins are hunted by humans, and killed inadvertently as a bycatch of fishing.
Survival of some bottlenose populations is threatened. They can swim up to 300 metres below the surface of the ocean.
They remain submerged for up to 20 minutes, and are capable of bursts of speed of around 30mph.
Dolphins have sharp eyesight but use echolocation to explore and search out prey when visibility is limited. They also communicate through pulsed sounds, clicks and body language.