© Edward Kendall
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Among the most difficult birds to identify are the birds that have abnormal plumage, whether it be color variation, a bill deformity, or missing head feathers. These plumage variations aren’t in any field guides, and sometimes the unusual plumage removes key field marks. If you see a strange-looking bird, use size, shape, and behavior to help identify the bird. Comparing the strange bird with other birds nearby can be helpful.
Project FeederWatch collected data about plumage variations from 2000 to 2011. Between 2000 and 2007, 1,605 unusual-looking birds were reported with a variety of plumage oddities. Although that sounds like a high number of strange-looking birds, given that FeederWatchers report about 5.5 million birds each winter, only a very small fraction of birds seen by participants have any kind of plumage abnormality.
Albinism is a genetic mutation that prevents the production of melanin in the body. Leucism is a genetic mutation that prevents melanin and other pigments from being deposited normally on feathers. Leucism comes in two main varieties — paleness, an equal reduction of pigment in all feathers; and pied, an absence of pigment in some feathers creating white patches.
Interestingly, some colors come from pigments other than melanin, such as carotenoids. Albinism only applies to an absence of melanin; consequently, it is possible for a bird to be albinistic and still have color. Leucism, on the other hand, applies to all pigments.
Albinistic birds have pink eyes because without melanin in the body, the only color in the eyes comes from the blood vessels behind the eyes. It is possible for a bird to be completely white and still have melanin in the body, as when a white bird has dark eyes. In this case the bird would be considered leucistic because the mutation only applies to depositing pigment in the feathers.
To further confuse things, occasionally a bird will lose feathers in a close call with a predator. When this happens the new feathers sometimes grow in white and then change back to the normal color at the next regular molt. This kind of white coloring looks like leucism but is not.
Learn more about albinism and leucism terminology.
Melanism is color variation referring to the excessive deposition of the pigment melanin. This results in feathers that are darker than normal. This color variation is far less common than leucism.
The color variation called xanthochroism refers to yellowish or orange pigments replacing normal coloration, usually red. FeederWatchers often report seeing strangely colored House Finches that they believe have xanthrochroism. However, House Finch coloration varies widely, and research has shown than most of the variation is diet-related rather than a pigment abnormality.
FeederWatchers often report seeing strangely colored House Finches that they believe have xanthrochroism. However, House Finch coloration varies widely, and research has shown than most of the variation is diet-related rather than a pigment abnormality.
All male House Finches have the same potential for yellow, orange, or red coloration. Researchers who kept House Finches in captivity found the red plumage replaced by yellow unless a carotenoid pigment was mixed in with their food during molt. In the wild, three carotenoid pigments found in natural foods give House Finches their color. Beta-carotene produces yellow to orange colors, isocryptoxanthin produces orange colors, and echinenone produces red colors. Yellow House Finches are frequently seen in the southwest and Hawaii where natural foods are low in some of these carotenoids. In the east birds often feed on the high-carotenoid fruits of ornamental plants.
Sometimes FeederWatchers observe birds with odd looking bills. Scientists are studying this phenomenon in Alaska, where the problem seems to be most prevalent. Colleen Handel, a biologist with the United States Geological Survey’s Alaska Biological Science Center, has compiled reports of deformities in more than 25 species. Deformities are reported most frequently in Black-capped Chickadees. A cause for the deformities has yet to be determined. Learn more about Colleen’s research.
From 2000 through 2006 Project FeederWatch collected 215 reports of bill deformities, representing 38 species from 38 states and provinces. As with Colleen’s data, Black-capped Chickadees were reported most frequently, making up 30% of the reports. House Finches were reported the second most frequently with 21% of reports. The majority of bill deformity reports came from Alaska–31% of all reports received, while 12% of reports came from California, the state with the second highest total. FeederWatch is providing summaries of reported bill deformities to Colleen to assist in her research.
Each year FeederWatchers report several cases of bald-headed birds, mostly Blue Jays and Northern Cardinals.
One possible explanation for this phenomenon is an abnormal replacement of feathers (molt). Most bald-headed-bird reports occur in summer and fall, which are typical molting times. Many of these strange-looking birds may be juveniles undergoing their first prebasic molt, which produces the first winter adult plumage. For some unknown reason, the bald birds may have dropped all of their head feathers at once. Staggered feather replacement is the normal pattern.
Other cases of baldness may result from feather mites or lice, or some environmental or nutritional factor. But no one knows for sure, and the condition has not been well studied. Fortunately, new head feathers grow in within a few weeks.
An interesting article on the topic of bald birds was published in the Buffalo News. You can read it here.
Once in a while we see something incredibly unusual, like this very strange looking Blue Jay that Jean Kuns found in her yard in Germantown, Ohio, in December 2006. Jean wrote “We’ve nicknamed him Papa Smurf!” We’ve never seen anything like it; have you?