Bottlenose Dolphins Are Even More "Right-Handed" Than We Are

Bottlenose dolphin (Tursiops truncatus). Asher Davidson/Shutterstock 

Ninety percent of us are right-handed, with the preference appearing in the womb and nine-tenths of infants sucking their right thumb. But what about other animals? Toads are right-handed, kangaroos tend to be lefties, and dogs wag their tails to the left or right depending on their mood. Now a new study confirms that bottlenose dolphins lean to the right, even more so than we do.

A team led by Florida’s Dolphin Communication Project recently assessed the feeding behavior of bottlenose dolphins off Bimini in the Bahamas. In particular, they looked at crater feeding, a tactic that involves a dolphin swimming low against the seafloor, identifying a hidden morsel using “razor buzz” echolocation clicks, and then grabbing it out of the sand with its long snout.

Just before the dolphins launch at their prey, they stop swimming forward and quickly spin to the side in a 90 to 180-degree turn. But which side do they prefer?

To find out, the researchers recorded 709 turns made by at least 27 different dolphins between 2012 and 2018. Overall, 705 of these turns, equating to 99.44 percent, were to the left, with just one lone dolphin turning to the right a total of four times.

Twisting to the left actually suggests a right-side bias, because it places the dolphin’s right side and right eye close to the ocean floor as it hunts. The researchers believe that this preference may be related to more sensitive eyesight in the right eye or the fact that dolphins tend to produce echolocation clicks using the phonic lips on their right side.

A dolphin turning as it crater feeds. Kaplan et al./Royal Society Open Science 2019; CC BY 4.0

The unique dolphin that spun to the right had an abnormally shaped right pectoral fin, but this isn’t necessarily the cause of its unusual lateralization as another dolphin had a damaged right fin while a third had no right fin, yet these two animals still turned to the left.

The authors note that bottlenose dolphins aren’t the only cetaceans to display a preference for their right side when employing certain feeding strategies. Dusky dolphins, orcas, and fin, humpback, blue, Bryde’s, sei, and gray whales all do too. Meanwhile, the majority of Ganges river dolphins, an endangered and elusive species that’s pretty much blind, swim right side down, continuously echolocating as they move. It’s also been documented in various birds and fishes.

The team thinks the dolphins may be biased due to the lateralization of their brains. The right eye corresponds to the left half of the brain, and the animals may be better at processing information collected through sight and echolocation in their left hemisphere. Previous studies have found that dolphins perform better at visuospatial, numerosity, and pattern discrimination tasks when using their right eye.

However, to find out exactly what gives the dolphins their right-side bias when feeding, we need more research. “Advances in non-invasive brain imaging techniques hold the potential to further explore the link between behavioural laterality and hemispheric specialization and sensory and cognitive processing,” the researchers write in Royal Society Open Science.

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