Plumage that is abnormally whiteAn an abnormal reduction in the deposition of pigment in the feathers is known as leucism. 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.” Causes include genetics, or injury, disease, or malnutrition.
This unusual American Robin was banded on 7 Oct 2007. It was an adult female undergoing its fall molt. The breast feathers were normal. However, nearly all of the incoming feathers on the wings, tail, and body that are gray in normal robins were full or partially "frosty" looking. Typically when abnormal white feathers are seen on birds, the entire feather is white, as in the first example. Partially white feathers like this are something RRBO encounters only rarely, and not to the extent found on this bird. The bird was re-sighted the following week.
Plumage that is abnormally orange
Tricks Exotic Shrubs Do: When Baltimore Orioles Stop Being Orange (pdf) by Tom Flinn, Jocelyn Hudon, and Dan Derbyshire -- article from Birding magazine.
Diet explains red flight feathers in Yellow-shafted Flickers in eastern North America. Hudon, J., R.J. Driver, N.H. Rice, T.L. Lloyd-Evans, J.A. Craves, and D.P. Shustak. 2017. The Auk: Ornithological Advances 134:22-33.
orange- or yellow-colored House Finches (Carpodacus mexicanus). Perhaps some lack in the diet combined with ingestion of a red pigment like rhodoxanthin that contributed to the orange color as well as the crimson color of the red plumage. Other orange cardinals have turned up in the literature and on the Internet, beginning in the late 1990s, lending some credence to the role of honeysuckles and rhodoxanthin in this plumage variation.
An 'orange variant' Northern Cardinal. (pdf) Hansrote, C. and M. 2000. North American Bird Bander 25:1-3.
And now, a white/pink cardinal! Ohio Birds and Biodiversity.
The yellow cardinal lives on. Ohio Birds and Biodiversity.
RRBO has banded a half-dozen Ruby-crowned Kinglets (Regulus calendula) with at least some orange crown feathers rather than salmon red, all since the year 2000. Examples of two individuals are shown below. This may also be due to a dietary deficiency.
Abnormally dark plumageWhen birds have plumage with excess pigment, usually the dark melanin pigments, they are known as melanistic. This Mourning Dove (Zenaida macroura) was seen in the Dearborn yard of Julie Craves and Darrin O'Brien on 8 Apr 2006. The second photo shows it compared to a normally-colored Mourning Dove.
The first secondary feather on one wing of this American Goldfinch (Spinus tristus), banded 20 Aug 2010 was completely black on the underside, rather than having a white base. When melanism occurs, it seems that it typically affects all feathers. RRBO has not documented a single melanistic feather or patches of melanistic feathers on any birds, much less the thousands of goldfinches banded on campus.
More information on abnormal plumage coloration
Davis, J. N. 2007. Color abnormalities in birds: A proposed nomenclature for birders. Birding 39:36–46.
David Sibley's web site: Abnormal coloration in birds: Melanin reduction.
British Trust for Ornithology's Abnormal Plumage Survey page.