Here in Cape Coral, Florida, I have noticed that a small population of our Burrowing Owls have very dark, almost black eyes, while the majority of them have brilliant yellow eyes. We first began noticing this a few years ago when we photographed an owl with the black eyes, which was very rare. Then we photographed an owl with one black eye and one yellow eye. I have seen siblings from one brood with some having black eyes and some having yellow eyes. This phenomenon occurs in both adult and juvenile birds.
Does anyone have a scientific reason for this?