Male and female Blue Tits looks almost the same to the human eye but not to each other. The pulmage of both sexes includes strong ultraviolet, reflectance, which makes the birds more conpicuous to each other agianst the background colors of the woods in which they live. Males also have a brillant purple crown patch that we cannot see. The males display ultraviolet crown prominently during courtship, especially in the early morning light. Consistent with the process of sexual selection, females prefer males with brightest crown patches. They also pair assortatively: those with the brightest UV reflectance in their own plumage pair with the most brightly colored males.
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