Dolphins change their vocalisation in response to interaction with humans, a factor that might be important to vets and other people dealing with dolphins in aquariums or in the ocean.
Dolphin researcher Melinda Rekdahl is the first to show that physical and social environments can alter dolphin communication during different activities such as feeding. She studied the behaviour and communication abilities of bottlenose dolphins in Moreton Bay for her Honours degree at the University of Queensland School of Integrative Biology.
Ms Rekdahl has also volunteered as a research assistant on many other dolphin research projects. In 2004 she had an internship at the Dolphin Research Centre in Florida Keys where they focused on cognitive research on captive animals. Then she decided her focus was wild populations.
In 2007 she worked in Mozambique as a marine research and volunteer coordinator for All Out Africa, involved in dolphin, turtle and coral reef research and conservation.
During her Honours year in 2005 and 2006, Ms Rekdahl studied120 dolphins from groups of wild dolphins in Moreton Bay, captive dolphins at Seaworld and provisioned (wild but handfed once a day) at Tangalooma Wild Dolphin Resort.
While dolphins display a range of vocalisations, it was noticeable that the whistle category used most often by the dolphin groups varied depending on the behaviour of the group.
“The captive and provisioned dolphins whistled more than the wild dolphins while feeding, with captive dolphins showing the highest rate of whistles,” she said.
“Feeding was the behaviour most influenced by humans in the captive and provisioned environment.
“Human interaction through the provisioned feeding environment seems to lead to different vocalisations being used.”
A group of dolphins swimming under water. Photo courtesy Melinda Rekdahl.
She said the provisioned dolphins didn’t display a wider range of sounds “rather they produced different categories of sounds more often than the wild dolphins while feeding and carrying out other behaviours”.
In different activities – provisioned feeding, provisioned socialising, provisioned milling, wild feeding, wild socialising and wild milling – the provisioned dolphins produced different categories of whistles, with a generally higher rate of whistle production in the provisioning environment.”
Ms Rekdahl said it was not possible to say what the purpose of their vocalisations may be, “we can simply say with the data that we have available that they produced different categories of whistles in different contexts.”
She said more research is required into categorising whistles into less broad 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”.
“Furthermore, 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.”
A pair of wild dolphins swimming near Mozambique. Photo courtesy Melinda Rekdahl.
Following her dolphin research she has turned her attention to the social communication of humpback whales as she works towards her PhD. She says a large part of her research involves looking through past recordings spanning over 20 years to analyse the temporal variability in their social communication.
However, she is not permanently in the lab, and is able to enjoy the thrill of whale watching from a boat, collecting data from the east coast population of humpback whales as they pass during their annual migration.
Humpback whale communication is different from that of dolphins in a few ways. Male humpback whales produce complex and rapidly changing acoustic breeding displays called song, which dolphins do not do.
“Their vocalisations are also considerably lower in frequency than dolphin vocalisations which presumably reflects their function in their social systems – humpbacks’ vocalisations need to travel further underwater so lower frequency signals are better,” she said.
She explained another difference between whales and dolphins is their social system, which is less complex than that of dolphins.
“Humpback whales have no known long term associations and they associate in small unstable groups, whereas dolphins are well known for their complex fission-fusion societies with sometimes long term and often stable associations where individuals maintain strong social bonds. Therefore, the differences in their social communication most likely reflects their social systems.”
However, humpbacks do also produce social vocalisations which are used in close range social interactions between mothers and calves, for example, but also between males and females, and whales of the same gender.
“Their social vocalisations appear to be complex and we still know little about the function these vocalisations have in their social systems and how stable they are through time,” she said.
“We already know through the excellent work of one of my supervisors, Dr Rebecca Dunlop from the University of Queensland, that the east coast population of migrating humpback whales produces 34 different social vocalisations in various behavioural contexts and in different social groupings.
“I will be continuing to explore the use of these social vocalisations in this population as well as look at the stability of these signals through time.”
Â© Sue Cartledge