When gannets dive into the sea to catch fish, they roll either to the left or the right according to their individual preference, much like how most people have a dominant hand.
The preference for one side of the body over the other, or laterality, occurs in many animals. Many primates, like humans, have a dominant hand; cockatoos tend to be left-footed and bees prefer to turn right when they enter an open cavity, while blue whales seem to have different preferences for different tasks.
Ashley Bennison at the British Antarctic Survey and his colleagues attached accelerometers to 71 northern gannets (Morus bassanus) on the coasts of Ireland and Wales and tracked their movements for roughly three days. All the birds were tending to chicks aged 3 to 4 weeks, which meant they needed to hunt for food out at sea every day.
When gannets spot their prey, they roll to one side before plunging into the water. The accelerometers successfully recorded 2133 dives by 51 birds. Of this group, 22 would consistently roll to the right during their dives, 26 would roll to the left and three had no preference.
The researchers also found that gannets had a strongly preferred dive angle, though this didn’t seem to predict whether they rolled left or right.
Laterality is thought to result from the two hemispheres of the brain being specialised for different tasks. “Because the brain is concentrated on one side for undertaking very specific behaviours, it allows your brain and your body to develop the ability to multitask,” says Bennison.
In contrast to us, gannets seem to be fairly evenly split between left and right-handers. It isn’t clear why most people are right-handed, but some researchers think it is due to social factors.
“When you look at humans, we are predominantly right-handed and that allows us to sort of coordinate an easy life in terms of tool use,” says Bennison. “When you see a more even split, like we’ve got here, it means it’s a behaviour that has come about because the individuals are engaging in more complex tasks by themselves.”
The findings represent the first time that laterality has been seen in a foraging seabird. “Prey capture and foraging are an incredibly important part of any animal’s life to the point of success or failure,” says Bennison, who hopes to explore whether “handedness” has an effect on where or how birds forage.