Intersting things about bird vision

I am currently working on a research paper for my evolution class. My topic is the evolution of UV vision in birds. I am reading through a bunch of research on the topic and then summarizing how and why UV vision evolved. It is not original research just a summary of what is out there on the topic. Here are a few interesting things I have learned.

• Most birds have four types of cone cells in their eyes so they can detect billions of colors. In contrast humans have three types of cone cells and can only detect 10's of millions of different colors.
• The pigeon is a pentachrome so it has five types of cone cells in it's eye.
• Some birds select their mates based on UV color patterns in the feathers which are undetectable to human eyes but are clearly seen by the birds.
• The Common Kestrel hunts it's prey the vole by following a urine trail it leaves which also reflects UV light.
• Most animals can see within in the UV range; placental mammals cannot (except bats) and snakes cannot.
• UV reception in birds is the difference of one amino acid mutation in the gene that codes for opsin.

This stuff is pretty interesting to me. Can you imagine seeing things like a bird does? Can you imagine how much brighter and more colorful the world would be? It is pretty cool.