Crows, Like Humans, Prefer Their Left or Their Right While Using Tools

Crows are known for their ability to use tools. Now, scientists have found that these birds have a preference for either their left or right side--just like humans are left- or right-handed.

These crows, called New Caledonian crows, are some of the most innovative tool users in the animal kingdom. They use sticks to extract larvae from their burrows. Interestingly, these crows prefer either to hold their tools on their left or the right side of their beaks.

So why do the crows exhibit this preference? It could be due to their eyesight. The birds' extreme binocular vision-characterized by an unusually wide field of view in comparison to other species-actually helps the crows see better with one eye at a time. By holding their tool on either their right or left side, the crows show a preference to seeing with either their left or right eye.

"If you were holding a brush in your mouth and one of your eyes [was] better than the other at brush length, you would hold the brush to that its tip fell in view of the better eye," said Alejandro Kacelnik, one of the researchers, in a news release. "This is what the crows do.

Interestingly, the crows use their binocular vision for better monocular vision, allowing each eye to see further toward the other side of the beak. The birds' unusually wide binocular field is among the first known example of a physical adaptation to enable tool use.

"Binocular vision is often connected to allowing the brain to compare the images seen by each eye, inferring properties of the scene from the differences between these images," said Antone Marttinho, one of the researchers. "We thought that their binocular fields would facilitate binocular vision, perhaps allowing the birds to judge the distance from tool tip to target. It turned out that, most frequently, they only see the tool tip and target with one eye at a time."

The findings reveal a bit more about how these birds use tools. More specifically, it reveals a bit more about the adaptations they have developed to accomplish their goals.

The findings are published in the journal Current Biology.

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