In a previous video we learned about birds that have unusually shaped eyes, like the
square pupil on a King Penguin. While doing the research for that video, I found THIS bird.
This is a Wood Pigeon. See that unusual oval shape? So I asked about it.
And a birding Youtuber called My Birding Year dug up a fact which upended my
assumptions and sent me on a hunt across the internet for facts about pigeon and doves.
And after all that research I still need your help! So let's
dive into this weird mystery of dove eyes.
See how its eye is oval-shaped? My first thought was, wow, wouldn't that make its vision worse?
Oddly shaped pupils exist in animals, but they are all symmetrical. Goat.
Cat. Cuttlefish. This pigeon has an asymmetrical pupil, so the light entering its eyes would be
asymmetrical. I asked "Their irises look so different! Any idea why they have the oval shape?"
My Birding Year wrote back,
"due to a spot of dark pigment in the iris, the pupil seems to be non-circular."
So I went back and looked at pictures of pigeons. Looking at pictures of pigeons
honestly isn't that unusual for me, because I write about birds almost every day,
but this time I was staring intently into their eyes. Pigeons. Doves. What is up with your eyes?
[Montage of pigeon and dove pictures,
ending with a well-lit wood pigeon eye showing the iris pigment]
There it is. Dark pigment on the iris. And a round pupil. So the vision mystery is solved.
They have a round pupil just like most birds, and their vision is normal.
But now why do they have this pretend oval eye?
My Birding Year "No idea what advantage the dark pigment on the iris gives"
So I dove into more pigeon and dove pictures, to see if I could find more fake oval pupils.
[montage
of pigeon and dove pictures]
There are so many! This is one of those times when you discover a new fact in the world that
has been right in front of you all along, and you can never un-see the fake oval eyes in pigeons.
I even found out how it works. The pigeon iris has a base layer of dark pigment,
with red and yellow pigment cells on top. So all you need to make a dark spot is
for there to be a small gap in the upper cells, letting the darkness show through.
But the thing is, there is no answer I can find anywhere on WHY this exists. There
is only one clue, and it comes from a completely different bird.
Oystercatchers are shorebirds that eat whatever small animals they can
find, from worms to molluscs to fish. The male and female plumage is exactly the same,
and the only sure way to tell them apart is by DNA testing. That is,
until 2008, when some researchers studying Black Oystercatchers found that there was a visual
identification technique that was 94% effective. They call it eye flecks. Female oystercatchers
have a big dark patch on their yellow iris, or several dark flecks. Males either have no dark
flecks or small ones. This might be a method that Oystercatchers use to identify possible partners.
This sounds like a promising avenue of study to solve the pigeon eye mystery. But I don't have
a set of pigeon information to work with, with identified male and female pigeons and a picture
of their eye. Also it is usually very hard to identify male vs. female pigeons without a DNA
test. So I'm asking you for help. If you have access to a pigeon or dove which is known to be
male or female, would you please tell me a) what species of pigeon or dove it is and b) does it
have the false oval pupil. Or if you know someone with a pigeon or dove, would you please ask? I'm
hoping that if we collect enough observations that we can get to the bottom of this mystery.
I look forward to hearing from you. Until then, you can subscribe to keep
learning about birds or watch one of these other videos which reveal bird secrets.
Thanks for stopping by this week to learn what makes Life awesome!