Researchers in the Bahamas studying a group of dolphins made an intriguing discovery: most of the group had a right-side bias, much like most people are right-handed.
Dolphins are cetaceans: mammals that live in water. Scientists currently identify at least 40 dolphin species, some of which live in seas or oceans and some of which make freshwater bodies their homes.
These cetaceans have attracted the interest of both the public and zoologists, as well as their playfulness, complex social networks and behaviors, and showing what might be different emotions all hint at a high intelligence level.
These and other characteristics have prompted some researchers to compare them with humans.
New findings, recorded in Port St. Lucie, FL, St. Mary’s College of Maryland, and Hunter College in New York by a team of investigators associated with the Dolphin Communication Project now suggest that dolphins that look like humans in another way.
In a study paper published in the Royal Society Open Science journal, the researchers concluded that most dolphins may have a right-side bias, according to their findings over 6 years, much the same as most humans have a right-hand bias.
The team of researchers studied a group of 27 bottlenose dolphins located off the coast of Bimini in the Bahamas, one of the most widespread dolphin species. From 2012 to 2018, the researchers made their observations.
The dolphins were watched as they were engaged in crater feeding a food foraging process involving using echolocation to locate prey under the sand.
Echolocation includes emitting different surface sounds that bounce off. The mammals can determine where their food sources might be by listening to these echoes. When a dolphin “catches” an echo while feeding the crater, they dive into the sand to dig for prey and shove their heads.
As the team started to follow these dolphins, they were intrigued to note that the dolphins made a sharp turn with their heads just before digging into the sand.
During the study period, 709 such turns were made by the dolphins. Every dolphin turned their heads to the left, except for one, every time they dived in.
Only one dolphin turned his head to the right, which was consistent as well.
The behavior of the bottlenose dolphins as they dive into forage indicate that most of them have a right-side bias, shifting to the left shows that they prefer to face the ocean floor with the right side of their heads.
The reason for this preference remains unclear, as with human right-handedness.
First author J. Daisy Kaplan, Ph.D., and colleagues put forward some hypotheses in the study paper as to why bottlenose dolphins may mainly be right-sided.
“A right-sided feeding bias in dolphins may have a physiological drive,” the author writes.
They’re explaining that, in dolphins, the larynx is situated to the left, “to provide room for a larger right pharyngeal food channel.” This may explain why most of the observed dolphins turned their heads to the left as they dove for prey.
Another theory has to do with nose tissue asymmetries that enable dolphins to emit echolocation sounds, the tissue structure on the right side, researchers suggest, is larger than that on the left.
“The bottlenose dolphin possesses the second-largest brain-to-body mass ratio of any mammalian species. Thus, we would expect a high degree of hemispheric specialization in the dolphin brain,” In their study paper, the researchers conclude.
Nevertheless, they acknowledge that “How this hemispheric specialization correlates with lateralized behavior remains unclear.”
In the future, the researchers hope that advances in brain imaging techniques will enable zoologists to gain further insight into the equivalent of handedness in dolphins.


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