Eye-opening New Research Helps Us Understand How Birds Communicate

One species of bird is proving that eyes provide not only a window to the soul, but also an effective means of warding off unwelcome nest competitors.

All in favor of new research that helps us understand how animals communicate, say eye.

A new study strengthens the case that jackdaws, crow-like birds found in Eurasia and Africa, use their eyes to communicate with other members of their own species—an ability that, up until now, was thought to only exist in humans and other primates. 

Jackdaw eyes bear some resemblance to those of humans—dark pupils and colorful irises surrounded by white sclera. In fact, a 2009 study found evidence that hand-reared jackdaws could follow a human gaze to tell what a person was looking at. The new study, conducted by Gabrielle Davidson of the University of Cambridge and published in Biology Letters, is the first indication that one jackdaw can use its eyes to send a message to another. 

"Jackdaws are unique among the crow family in that they nest in cavities in trees. These hollows are natural—the birds cannot excavate their own nest cavities as some woodpeckers do—so they have to compete for a limited resource, Davidson said. “And because jackdaws nest in close proximity to each other, they fight a lot to gain the best nesting sites.” Fights often flare up when a competing jackdaw approaches a resident’s nest.

Davidson wanted to know if the defending bird could ward off the offensive player by using its eyes alone. In advance of last year’s spring breeding season, she installed one of four different pictures in a hundred jackdaw nest boxes on the outskirts ofCambridge. The pictures were either: black (the control), a pair of jackdaw eyes, a pair of jackdaw eyes on a jackdaw’s face, or a jackdaw’s face with a pair of black rook eyes. She then filmed the effect of the different pictures on approaching intruders.

After studying 40 videos of jackdaws peeking into each other's nest boxes, Davidson found those containing the picture of a jackdaw with bright eyes were much more likely to deter other birds from landing on the box, and that the offending birds spent less time near those particular nest boxes.

"Before now we knew very little about why some birds have brightly colored eyes. In jackdaws, the pale eyes may function to improve their ability to defend their nest and chicks from competitors,” she said. “It also raises the question of whether this is unique to jackdaws, or if other cavity nesting birds also use their eyes in a similar way.”

A question that invites more research to help us understand how birds and other animals communicate with each other? Now that’s worth keeping an eye out for.