Do seabirds have polarised vision?
Do birds that hunt in water or below water have polarised vision, as it would be a good advantage for them to be able to see through the water?
A lot of animals have polarised vision, so that's actually a good suggestion. The other thing that I think is really interesting is birds that dive under the water. Earlier on we were talking about the way that humans become long sighted when they look under water; well birds that dive under water don't. They can actually accommodate up to 60 diopters, meaning that they can really change the shape of their lens. They do this by ramming their lens up against a very solid iris, and they form a great big bulge at the front of their lens.