Dolphins Vocalise More When Fed
Dolphins’ Vocalisation Changes when They Interact with Humans
Nov 27, 2008
Dolphins change their vocalisation in response to interaction with humans, a fact that might be important to people handling dolphins, whether tame ones or wild in the ocean.
Dolphin researcher Melinda Rekdahl of the University of Queensland School of Integrative Biology in Australia is the first researcher to show that dolphins’ physical and social environments can alter their communication during activities such as feeding and socialising.
She presented her findings on dolphin vocalisations at the International Biology of Marine Mammals Conference in Cape Town, South Africa, in November 2007.
Rekdahl has studied wild bottlenosed dolphins in Moreton Bay, Queensland, captive dolphins at the Dolphin Research Centre in Florida Keys, Miami, and wild dolphins in Mozambique.
While dolphins display a range of vocalisations, she said, it was noticeable that the whistling used by groups of dolphins varied depending on the behaviour of the group.
Dolphins don’t just make one whistling sound, they make a variety of whistles, short and long, fast and slow. Dolphin whistles and pulses are mainly used for social communication while their eco clicks are used for feeding and navigation.
Captive Dolphins Whistle More Than Wild Ones
During 2005 and 2006, Ms Rekdahl studied120 dolphins from groups of wild dolphins at the Moreton Bay Research Station, captive dolphins at the nearby Sea World, and wild ones at Tangalooma Wild Dolphin Resort.
Wild dolphins at Tangalooma are hand fed by visitors each day. Rekdal calls this ‘provisioned’.
She spent two weeks with each group and recorded hundreds of hours of dolphin noises, including burst pulses and clicks and 10 hours' of whistles.
She recorded the rates, types and frequency of whistles among the groups during feeding, socialising and milling.
“The captive and provisioned dolphins whistled more than the wild dolphins while feeding, with the captive dolphins showing the highest rate of whistles,” she said.
Feeding was when the captive and provisioned dolphins had the most interaction with humans, and so this was the behaviour most influenced by humans.
The hand fed dolphins didn't display a wider range of sounds than their wild cousins, “rather, they produced different categories of sounds more often than the wild dolphins while feeding and carrying out other behaviours”.
Vocalisation Important for Social Cohesion
Dolphins are well known for their complex ‘fission-fusion’ societies, she said, “with some long term and often stable associations where individuals maintain strong social bonds”.
They have a range of varied vocalisations that contribute to the social cohesion of dolphin pods, but very little is yet known about them, Ms Rekdal said, and it was too soon to say why the hand fed dolphins whistled more than the wild ones.
“We can simply say with the data that we have available that they produce different categories of whistles in different contexts.”
More Research Needed into Dolphin Vocalisation
More research is required into categorising whistles into more defined categories, “over more behavioural contexts and a longer time period to investigate further the differences in the contextual use of whistles and in total whistle repertoire,” she said.
It was unclear whether the hand fed dolphins’ greater whistling related the fact that they were being fed, or to some other factors, such as their social status.
“Identifying the association patterns of the provisioned dolphins outside of the provisioning area and the stability of their social grouping is crucial in determining whether the difference in whistle use we observed may be just related to their different social and physical environment and due to a flexible whistle repertoire, or whether it may reflect more specialised whistle usage by the provisioned dolphins relating to their provisioning environment.”
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