Jackdaw Birds Use 'Stink Eye' To Ward Off Competitors, First Time The Behavior Seen In Non-Primates

If you ever thought a bird was giving you the stink eye, but quickly wrote it off as just a figment of your imagination -- you were probably right in the first place. New research is helping scientists better understand how birds use their eyes to communicate, a characteristic thought to exist only in humans and primates.

A new study of Western jackdaws found that the dark-feathered birds, which are in the crow family and can be found in Eurasia and Africa, use their piercing stare to ward off competing jackdaws. The jackdaw's eyes, with their dark irises surrounded by white pupils, bear some resemblance to those of humans.

The report, published in the journal Biology Letters, looked at whether jackdaws could scare off a competitor just by using its eyes. Researchers rigged up several jackdaw nest boxes with photos that were either completely black (the control), showed 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.

"Animals often respond fearfully when encountering eyes or eye-like shapes," the researchers wrote. "Although gaze aversion has been documented in mammals when avoiding group-member conflict, the importance of eye coloration during interactions between conspecifics has yet to be examined in non-primate species."

After filming the jackdaws' reactions to these photos, researchers discovered that the birds spent the least amount of time near the nest boxes that contained the picture of a jackdaw with bright eyes.

So why jackdaws? According to Gabrielle Davidson, a scientist at the University of Cambridge who led the study, male jackdaws have a habit of competing with each other for the best nesting spots. Fights often occur when one jackdaw approaches another's nest. They also have a unique set of peepers.

"Jackdaw eyes are very unusual," Davidson said in a statement. "Unlike their close relatives, the rooks and crows -- which have very dark eyed -- jackdaw eyes are almost white and their striking pale irises are very conspicuous against their dark feathers."

Previous studies involving jackdaws' behavior have also noted the jackdaw's unique use of its eyes. A 2009 study found that birds that were hand-reared could study a human's gaze and tell what the person was looking at.

"We can communicate a lot via the eyes, and jackdaws do that as well, in my opinion," Auguste von Bayern, a zoologist at the University of Oxford, told National Geographic in 2009. "They are sensitive to human eyes because they are sensitive to their own species' eyes."