This stunning and unusual American Robin with a white breast was the highlight of our final day of banding for the fall 2009 season on 8 Nov 2009.
American Robins with abnormal plumage are not terribly uncommon, and a number of them are shown on our introductory page on odd plumages. It’s not too unusual to find photos of robins that were the “opposite” of our bird, with pale backs but normal breasts (in Minnesota, Saskatchewan, Iowa, Pennsylvania, and Utah). This robin — with a completely white breast with a normally-colored back, wings, and head — is the first we have heard of or encountered.
Most of the gray plumage on this robin, which was a hatching-year bird (born in 2009), was normally-colored. It did have a few partially white feathers on each wing. Most of these feathers were short and/or deformed. On the left wing there was one slightly brittle short feather with a bit of white, and one mostly white feather next to it.
This condition is usually called “leucism,” which is an abnormal reduction in the deposition of pigment in the feathers. Some leucistic birds appear entirely washed out or pale if the reduction of pigment is roughly equal in all feathers (some authors now call this “hypomelanism”). More often, pigment is absent in only some feathers, and this is known as pied leucism, or “partial amelanism.” Both the grayish-brown and orange/rust feathers on robins are colored by various types of melanin pigments.
There are a number of causes for this type of plumage abnormality. Some are environmental, including injury, disease, or malnutrition. Others are genetic. In the dozens of pied leucistic birds handled by RRBO, brittle or deformed white or pale feathers have never been noted. This tends to make me believe that this robin’s problems were genetic in some way. The bird appeared healthy otherwise.