Vibrant blue plumage of breeding male fairy-wren may be linked to their higher visual sensitivity to ultraviolet (UV) light.
Researchers found that different species of fairy-wren can have either violet or UV-type vision. Species with UV-type vision have greater sensitivity to UV/blue light and have blue mating plumage.
The UV vision makes the blue male plumage stand out more from their environment and is therefore more attractive to potential mates.
Read more at Monash University