For one species of bird, a stare a day keeps its enemies at bay.
New research shows that the Eurasian jackdaw (Corvus monedula), a medium-size, dark-feathered bird in the crow family, scares off competitor jackdaws with a withering look. (Related: “Bird With ‘Human’ Eyes Knows What You’re Looking At.”)
Scientists have long known that directed gazes can impart fear: Think about giving someone the evil eye or stink eye, for instance.
But humans aren’t the only ones with warning glances: Biologists have found that eyes, or even something that just looks like eyes, can be scary. Basking black iguanas, jewel fish, house sparrows, starlings, and jackdaws have all been known to flee from the sight of eyes, which may be interpreted as belonging to a predator. (See: “Revealed: How We Detect Fear in Others’ Eyes.”)
But University of Cambridge researcher Gabrielle Davidson wanted to know if birds also used dirty looks with their own kind—in particular, to scare off competitors.
She chose to study jackdaws because their eyes are especially visible, with large white irises that frame dark pupils against dark feathers.
To test her idea, she showed a group of wild jackdaws one of four different circles: a circle that had the front view of a jackdaw face, complete with white eyes; the same face, but with entirely black eyes; a black circle with a pair of only white eyes; and a control circle that was completely black.
The circles were placed directly behind the opening of a birdhouse so that they were easily visible to the wild jackdaws.
Since these birds make their nests in cavities similar to a birdhouse, seeing the white irises could be a signal to the bird that the area is occupied, the team suspected. (See National Geographic’s backyard bird identifier.)
What’s more, fighting another jackdaw for a nesting site could lead to injury or death, which gives the jackdaws a lot of incentive to be wary of invading another’s turf.
Davidson and colleagues then measured how long the birds stayed near the birdhouse when the different circles were displayed.
If the eyes did act as a threat to other jackdaws, then the birds should spend less time near the birdhouse and visit it less often when the circles that showed white eyes were displayed. This is exactly what the researchers found, according to the study, published this week in the journal Biology Letters.
No word yet on whether an eagle eye has the same effect.