Jackdaws Use Eyes to Communicate, Study [Video]

Jackdaws communicate with eyes to fend off rivals, a new study from Universities of Cambridge and Exeter shows.

Humans say a lot with their eyes. And, at least one theory says that the colored irises floating against a white background and black pupils isn't by chance and is an evolutionary strategy to help us follow our fellow humans' gaze.

The latest study found that even Jackdaws use eyes to discourage others from coming near their nests. Jackdaws nest in natural cavities in trees and guard them fiercely. According to researchers, this is the first time that eye-communication has been documented in birds.

The jackdaw (Corvus monedula) belongs to the crow family and is known to be highly sociable. These birds also have "mercy killings," in which sick or injured birds are killed by other members.

It's in the Eyes

Most birds have black or dark brown eyes, but about 10 percent of perching birds have bright eyes. Researchers in the current study wanted to know if jackdaws use these bright eyes to deter other jackdaws from coming close to their nests.

"Jackdaw eyes are very unusual. 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," said Gabrielle Davidson of the University of Cambridge, lead author of the study, according to a news release by University of Cambridge.

For the study, researchers placed four different pictures of jackdaws in 100 nest boxes. The pictures were either

• pair of jackdaw eyes,
• jackdaw eyes and face,
• jackdaw face with rook's eyes or
• black (control)

Researchers then filmed the behavior of other jackdaws when they saw the eyes in the nest. The video footage showed that these birds were least likely to approach the nest-boxes that had the face of jackdaws and eyes when compared to other nests.

"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. And because jackdaws nest in close proximity to each other, they fight a lot to gain the best nesting sites," Davidson explained.

The study is published in the journal Biology Letters.