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Dolphins recognise personal whistles – and urine

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Urine-sampling and signature whistling are the two unique ways in which dolphins identify and keep track of each other – and they are the first vertebrate to have been found to act in this way.

The findings are explained in a new study led by dolphin behavioural biologist Dr Jason Bruck of Stephen F Austin State University in Texas, and he believes they could even assist in tackling human obesity.

Working with Sam Walmsley and Vincent Janik from Scotland’s University of St Andrews, Bruck has established that dolphins recognise each other using “urine cues”. This is the marine equivalent of dogs sniffing the traces left by other dogs, but because dolphins are unable to smell they make the identification using taste.

“It is likely that dolphins use a lipid taste receptor to identify urine cues in their fellow dolphins,” says Bruck. “The gene that codes for that is called CD36. Most humans also have this gene, and it helps them determine when they have had enough to eat. 

“Humans lacking it are at higher risk for obesity. It is possible that dolphins can offer a better way to study the molecular anatomy of CD36 to help better understand how it works in people.”

The study also found that dolphins invent their own signature whistles during their first year of life and use these to identify themselves to others. This is said to be the first time a non-human has been shown to use an invented “acoustic label” to signal its identity.

20 or more years

Bruck’s research was designed to follow up on 1960s discoveries that dolphins in Florida would emit different sounds when separated from members of their group.

“Dolphins don’t have ‘voices’, because the pitch of their calls change as they dive deeper,” says Bruck. “Past research shows that dolphins can use each other’s whistles to address individuals. My previous research has revealed that dolphins can remember these whistles for 20 or more years, and now we know that they probably use them the way humans use names for recognition.”

Dolphins were able to integrate both forms of information, as demonstrated when the signature whistles of known animals were paired with urine samples from either the same dolphin or a different, familiar animal. The dolphins spent longer investigating the presentation area when the two samples matched.

Bruck’s recent dolphin communication and cognition research began in 2016 through a grant from the Marie Sklodowska-Curie Fellowship of the European Commission, with much of it carried out at Dolphin Quest in Bermuda, Oahu and Hawaii, where guests are said to see dolphins in sheltered, natural ocean lagoon settings while supporting conservation, education and scientific study. The research is conducted above water, using underwater speakers and hydrophones. 

Bruck says that although this phase of his research is complete, he plans to return to Bermuda  for further experiments. He also wants to investigate whether oil spills, chemical run-off and other human-derived ocean pollution can impede dolphins’ natural ability to signal to one another through urine sampling. The study has just been published in Science Advances.

Also on Divernet: Dolphins Guard Russian Warships Against Divers

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Knowledge-Wisdom
8 months ago

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