More than 90 per cent of human beings are right-handed, our preferences already existing in utero. But the study, published on Nov. 5, showed common bottlenose dolphins to have an even higher right-side bias than humans at more than 99 per cent.
Common bottlenose dolphins in the Bahamas use a foraging technique termed “crater feeding”, in which they swim slowly along the ocean floor echolocating prey before burying their beaks into the sand to catch their prey. Right before diving headfirst into their meals, the dolphins make a sharp turn, which researchers measured to determine side bias.
Researchers said a left turn keeps a dolphin’s right eye and right side close to the ocean floor, indicating a right-side bias.
“Virtually all turns recorded both from the 27 individually identified dolphins and from unidentified dolphins (99.44 per cent of turns) were to the left,” the study read.
Out of a study of 709 turns recorded from at least 27 different common bottlenose dolphins, researchers found this turn is almost always to the left, with the same direction taken in 99.4 per cent of the 709 turns recorded between 2012 and 2018.
Only four turns were made to the right and all of them were made by the same dolphin. In the study, researchers noted the dolphin had an oddly shaped right pectoral fin, but said two other dolphins with an abnormal or missing right fin still turned left, making the fin an unlikely cause for its left-side bias.
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Dolphins are by no means the first cetaceans to exhibit right-handedness. The team said grey whales and humpback whales show a population-level right-side bias when bottom rolling. Orcas, fin whales and blue whales also show a significant right-side bias when lunge feeding.
Several species of birds also show such preferences. Reindeer herds tend to circle in a counter-clockwise direction and giraffes move their left leg first when beginning a splay stance. Chimpanzees and gorillas show a significant right-hand bias, while orangutans were found to prefer the left.
According to the study, there are a number of possible reasons behind the team’s findings, including that it might make it easier for the dolphins to swallow prey as their food channel, which splits to pass around their larynx and is wider on the right than the left side.
The team also found dolphins produce echolocating clicks with the phonic lips on the right side of their head, meaning it could be beneficial for them if this side is kept nearer to the ocean floor.
Research also suggested dolphins’ bias could be linked to brain processing.
Not dissimilar to human beings, sensory information picked up by one side of the dolphin body is processed by the opposite side of the brain.
If visual and echolocation information is largely processed by the left hemisphere of the dolphin brain, the teams said animals might perform better at foraging if information is picked up by the right eye and ear.