Jackdaws communicate with one another using their eyes, according to a study published in Biology Letters. (Photo: Wikimedia Commons)

If you've ever looked into the eyes of a jackdaw and thought he was trying to tell you something, you may have been right (or insane-it's definitely one of the two). A recent study published in the journal Biology Letters suggests that jackdaws, a bird in the crow family, use their eyes to warn other jackdaws to say out of their nest. No non-primate has been shown to communicate with their eyes until now.

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"Jackdaw eyes are very unusual," said lead study author Gabrielle Davidson of the University of Cambridge, in England. "Unlike their close relatives, the rooks and crows-which have very dark [eyes]-jackdaw eyes are almost white and their striking pale irises are very conspicuous against their dark feathers." With blue-white irises, jackdaws are among the 10 percent of passerines, or perching birds, that have colored irises.

Jackdaws, which are found in Europe and parts of Asia and Africa, nest in cavities, and the limited amount of available cavities can lead the birds to fiercely compete for space. After observing jackdaws and noticing their eyes blazing brightly- and perhaps menacingly-from within these dark cavities, Davidson began wondering whether jackdaws use their eyes to communicate.

Davidson installed jackdaw nest boxes on the outskirts of Cambridge during the jackdaw breeding season. Into each nest she placed one of four pictures: a picture of just black, which served as the experiment's control; a pair of jackdaw eyes; a jackdaw face with eyes; and a jackdaw face with the black eyes of a rook.

Davidson let cameras roll on the nesting boxes, and at the end of the experiment she had 40 jackdaw videos. The videos revealed that jackdaws were far less likely to hang around nesting boxes containing the jackdaw face and eyes, marking the the first time a study has shown non-primates using their eyes to communicate to one another.

"Before now we knew very little about why some birds have brightly colored eyes," said Davidson. "In jackdaws, the pale eyes may function to improve their ability to defend their nest and chicks from competitors. 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."

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