What colors do birds see?

Five things that I have learned about the color vision of birds:

• Humans are sensitive to three peak wave lengths while birds are sensitive to four or five making them tetrachromats
• The structure of a bird's retina is much more complex than that of a human
• Birds have a deeper fovea which creates a larger surface area to hold more cones
• There is a strong connection between the habitat and the spectral senses of a bird
• Some birds, like the Kestrel, use their ultraviolet sight to detect the urine and feces of mice in a large cultivated field, therefore allowing them to find and capture them