Why are the Jackdaw’s eyes so steely blue? It’s a question that has been unanswered for years. But researchers from the University of Cambridge and University of Exeter have finally found a potential answer.

This great video explains the project and what the researchers found.

The team used pictures of jackdaws eyes and placed them inside nest boxes. They then recorded  approaching jackdaws to determine their reaction. When a pair of bright jackdaw eyes were present, approaching jackdaws spent less time investigating the nest boxes. When eyes were blacked out, jackdaws would often investigate boxes further.

The jackdaw’s eyes might therefore act as a warning signal to indicate that a nest site is occupied. Jackdaws often compete for nesting sites, resulting in injury or death, so being able to inform others that a nest site is already occupied could prove to be an adaptive advantage.

Researchers haven’t measured the brightness of individual jackdaw eyes, but would brighter eyes mean less competition over selected nesting sites? Only time and further research will tell.