I’ve taken a few fairly close snaps of Wood Pigeons (Columba palumbus) and noticed that the pupils of their eyes do not seem to be perfectly round. Same with a few other birds, I assumed it was just an aberration, however, I wanted to be sure.
It didn’t take much web searching to discover that other people have noticed this too. Someone asked about it recently on the RSPB website and got a reply from Hein van Grouw, who is apparently Senior Curator, Bird Group at the Natural History Museum:
“Yes, wood pigeons seem to have non-circular pupils. The pupil, however is circular but due to a spot of dark pigment in the iris the pupil seems to be non-circular. I have no idea what the reason (advantage) is for this. What I do know is that several other (tropical) species, mainly Fruit Doves, have it too.”
I must say though, it doesn’t look like pigmentation in the iris, it looks like a distortion of the edge of the pupil itself, at least in the photos I’ve taken. Oystercatchers have a pigment fleck too and you can tell what sex they are from this, apparently.
Wood Pigeons do seem to have really good eyesight regardless of the shape of their pupils, and perhaps partly because of them, they will veer off their flight path if they spot you walking below their course even through trees and can definitely see you from trees in the garden when you’re inside the house. That said, they will also completely ignore you if you don’t look at them and then take flight when they catch your eye. The eyes have it. (Hat tip to my Ladybird Farmer friend Simon for pointing that out).