In the same way that humans can be either left- or right-handed, crows -- who are known for being especially good at wielding sticks as tools, especially to pull larvae out of burrows -- favor either the left or right side of their beaks. But this may not have anything to do with the beak itself: Instead, a crow's beak "handedness" may have to do with their eyesight.
According to research published Thursday in Current Biology, these birds are compensating for the fact that one of their eyes is better than the other.
"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 so that its tip fell in view of the better eye," study author Alejandro Kacelnik of the University of Oxford said in a statement. "This is what the crows do."
The researchers performed tests to determine the eye dominance of nine crows and found that their dominant eye could reliably predict their preferred beak side -- if their left eye was stronger, they held the tool on the right side of their beak, which put the tip of it in front of the left side (and vice versa).
Humans don't have this same correlation: Only two thirds of us are right-eye dominant, but 90 percent of us are right-handed. But that's probably because we can move our hands (which hold tools) and our heads (which hold eyes) separately. Crows don't have that luxury.