There’s a female Tufted Duck on the lake at The Regent’s Park in London. Looking at it I marvel at how brilliant its eyes are:
Whenever I look at ducks I’m struck by how brilliant and contrasting their eyes are. Dark-headed ducks often have light coloured eyes and light-headed ducks often have dark eyes.
Why so brilliant though? What’s the evolutionary purpose of having extreme eye contrast? It can’t have anything to do with eyesight of the duck because the colour is simply a pigment on the surface the iris.
The answer I think, the reason that ducks have brilliant contrasting eyes, must be that ducks are delicious. Ducks are a prey species and vigilance is everything for their survival. With their eyes on the sides of their heads they can have a 340 degree angle of view. All that vigilance is worthless if they’re asleep and have their eyes closed though.
Having brilliant eyes tells all potential predators “I’m wide awake and watching your every move”, and tells all its flock, “I’m on guard and I’ll quack if I see anything that threatens us.” It’s such a simple, elegant, visual signal which uses so little energy to produce, yet has such a great effect on survival.
Here’s a male Tufted Duck.
It’s wide awake.