© Edward Kendall
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Among the most difficult birds to identify are the birds that have abnormal plumage or other characteristics, whether it be color variation, a bill deformity, or missing head feathers. These variations aren’t in any field guides, and sometimes the abnormality 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 unusual-looking birds from 2000 to 2011. Between 2000 and 2007, 1,605 unusual-looking birds were reported with a variety of oddities. Although that sounds like a high number of strange-looking birds, FeederWatchers report about 5.5 million birds each winter, making the number of reports of unusual-looking birds a very small fraction of birds seen by participants.
Albinism is a genetic mutation that prevents the production of melanin (but not other pigments). 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, although most consider true albinism to be an absence of all pigment.
Leucism refers to an abnormality in the deposition of pigment in feathers. There is some disagreement as to whether the condition is genetic or caused by pigment cells that were damaged during development. Whatever the cause, the condition can result in a reduction in all types of pigment, causing pale or muted colors on the entire bird. Or the condition can cause irregular patches of white, and birds with these white patches are sometimes described as “pied” or “piebald."
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 melanin in the feathers, not the absence of melanin in the body.
A third type of mutation that results in pied birds--birds that have white patches--is called partial albinism by some and leucism by others. The white patches are caused by an absence of pigment in some 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 and most frequently happens in the tail, causing a bird that lost its tail feathers to a predator to have an all white tail.
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 that 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 that the red plumage was replaced by yellow plumage 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. From 2000 through 2006 Project FeederWatch collected 215 reports of bill deformities, representing 38 species from 38 states and provinces. 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 provided summaries of reported bill deformities to researchers at the United States Geological Survey’s Alaska Biological Science Center.
Biologists there have been studying bill deformities, also known as Avian Keratin Disorder, for some time. In 2016 a team of researchers from the California Academy of Sciences, University of California San Francisco, and the USGS identified a novel virus that has been linked to Avian Keratin Disorder. Learn more about the research.
Each year FeederWatchers report several cases of bald-headed birds, primarily Blue Jays and Northern Cardinals. In most of the cases observed in late summer and fall, the affected birds have dropped their head feathers simultaneously during molting, resulting in individuals being nearly bald for about a week. Many of these strange-looking birds may be juveniles undergoing their first prebasic molt, which produces the first winter adult plumage. For Blue Jays, this molt pattern is considered normal, and this molt pattern happens with enough frequency in Northern Cardinal populations to be considered within the normal range. See two photos of a bald-headed Blue Jay posted in the Participant Photo Gallery by Bob Vuxinic. They show the jay bald and then 4 days later, with feathers starting to grow in.
If you notice a bald-headed bird of another species, it could be the result of an abnormal molt. Staggered feather replacement is the normal pattern for most birds.
Baldness also may result from feather mites, lice, or an environmental or nutritional factor. Often in these cases, there is evidence of growths or a scabby coating on the skin. For example, Northern Cardinals have black skin, and a different color skin on the head of a bald-headed cardinal would indicate an ailment.
No one knows for sure what causes baldness in birds, and the condition has not been well studied. Fortunately, in most cases new head feathers grow in within a few weeks.
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?