In April, GrrlScientist posted a picture of a blue house sparrow seen in April among normal colored birds. She commented on the nature of its mutation.
Birds and butterflies aren’t blue because of pigment but because of their surface texture of their feathers or scales, so I’m guessing that this is a structural change in the feathers.
It would be very interesting to get the local university to put up a mist net, band their catch, and perhaps pluck a feather or two. I’m curious about the genetics of family members — I wonder if some of the brown ones are heterozygous for blue feathers and how many ordinary sparrows it would take to find out. And will the chicks dig it?
GrrlScientist has a follow-up and more photos from the one who spotted this bird in Sydney, Australia, in April.