Jackdaws are the first birds known to communicate with their eyes.
In the past very little research has been conducted on whether or not birds communicate with their eyes, a University of Cambridge news release reported. New research suggests they use eye contact to intimidate other birds coming near 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," Gabrielle Davidson of the University of Cambridge, who led the study said in the news release.
Most birds have black eyes, but jackdaws and a number of other perching birds have colored irises; the researchers wanted to know if they used these bright eyes to communicate with each other.
Right before breeding season researchers installed different pictures in 100 jackdaw nest boxes. The pictures were black (for the control group), a depiction of jackdaw eyes, eyes on a jackdaw's face, or a jackdaw's face with black eyes.
"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 said.
The researcher looked at 40 videos of the jackdaw nests, and found the ones fitted with a jackdaw face and bright eyes were less likely to be landed on by other birds. The researcher suggests this mean the birds use their eyes to communicate and deter invaders.
"Before now we knew very little about why some birds have brightly coloured eyes. 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," Davidson said.