Strange Birds

Sometimes a strange-looking bird shows up at your feeder. The bird may look somewhat familiar, but it has odd coloration, white patches in all the wrong places, a featherless head, or a misshapen beak. We'll describe these abnormalities and try to explain why they occur.If the bird looks normal, but is simply an unfamiliar species to you, visit our online Bird Guide for identification help. Birds occasionally do wander outside their typical ranges, and we offer some reasons such rarities might occur.

Color Variants
Common birds show a surprising amount of color variation—watch a flock of American Goldfinches in spring and notice how the males range from pale lemon to vivid golden yellow. Other color oddities are a bit more confusing—you might see a bird that looks like a Dark-eyed Junco with a white head, a pure white bird shaped like a Blue Jay, or a European Starling whose plumage color looks much paler then usual. Most likely the bird really is what you think it is. Remember that size, shape, and behavior often help to identify a bird even when its plumage looks odd. Comparing the strange bird with other birds nearby can be very helpful. Try using color variations to help you keep track of individual birds—you may discover that your "special" bird has quite a personality!Some color variation—such as albinism or leucism—results from a bird's genetic makeup. The upper photo at right shows a leucistic Northern Cardinal. Notice its plumage, while not pure white, is very pale but it has some color in its wing feathers. Its crest and stout, red beak are still useful identification characters. In the lower photo, a partial albino Spotted Towhee visits a feeder. Its body and wings have pure white patches, but its distinctive rufous flank patch remains.
Other color variants are related to diet. A common example is color variation in male House Finches, as pictured at left—typical red plumage is shown in the top photo, orange in the middle and yellow at the bottom. Coloration may also reflect an individual's health and age.
Here are more details about some common color variations:
Albinism: All- or partially-white plumage. Albinism results from a genetic mutation that interferes with production of the pigment melanin. Birds that lack not just melanin but all pigments are called true or complete albinos. As well as pure white plumage, they lack pigment in their skin and eyes. Partial albinos have a pied appearance, with patches of pure white feathers.
Leucism: Extra-pale plumage. Leucism is related to albinism, but in this case the normal pigmentation is diluted rather than lacking, resulting in birds whose plumage is lighter than normal, but not pure white. Plumage patterns, such as a mask or wingbars, often remain detectable.
Melanism: Extra-dark plumage. Melanistic birds have a genetic mutation that results in an excess of dark pigmentation. Some cases also result from diet. Some species have a naturally occurring melanic form (or "morph"), for instance the Red-tailed Hawk.
Xanthochroism: (sometimes xanthism or xanthochromism) Yellowish or orange plumage (usually instead of red). May be caused genetically or by diet.
Erythrism: Reddish or rufous plumage. Some species have commonly occurring rufous form, for instance the Eastern Screech-Owl.

Bald-headed Birds
Every year the Cornell Lab of Ornithology receives reports of "bald-headed birds", mostly Blue Jays or Northern Cardinals such as the male at right. Most bald bird reports occur in summer and fall, which are typical molting times, when birds go through a normal replacement of feathers.Many of these strange-looking birds may be juveniles undergoing their first pre-basic 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. Other cases of baldness may result from an infestation of feather mites or lice, or from some environmental or nutritional factor. But no-one knows for sure, and the condition has not been studied widely. Whatever the reason, bald birds usually recover successfully from their serious "bad hair days", growing normal head plumage within a few weeks, and able to face the world again without shame!

Birds with Deformed Beaks
Sometimes birders observe birds with odd-looking beaks. Numerous Black-capped Chickadees with greatly elongated and down-curved upper beaks (such as the one on the left) were reported in 1998-1999 in southern Alaska, for instance. Scientists studying this phenomenon have yet to determine a specific cause. Bird beaks are much like human fingernails—soft structures that actually grow at a constant rate all the time. Many factors have been implicated in causing birds' beaks to grow abnormally, including structural damage to the beak, disease, parasites, nutritional deficiencies, genetic defects, exposure to extreme heat, and exposure to environmental contaminants.A slight malformation may not affect a bird's survival, but an extreme deformity may make normal feeding difficult if not impossible.Learn more from this article from Birdscope: Mysterious Bill Deformities Seen in Alaskan Chickadees.
Rare Birds
As many birders will attest, nothing is more exciting than identifying a new species in your yard, especially a rare bird—one that is out of its typical range. What causes birds to roam far from their normal range is never certain. Below are some possible explanations:
Certain species, such as crossbills and Pine Grosbeaks, may arrive en masse in response to scarce food in their northern homes. These irregular migrations are termed irruptions.
Migrating birds may be blown off course by the strong winds of hurricanes and other violent storms, or grounded by fog, heavy rain, or other adverse weather conditions.
Some birds, often juveniles, disperse northward after the breeding season in what is referred to as post-breeding or vagrant wandering.
Occasionally birds occur in new areas by migrating in a direction opposite to that expected, referred to as reverse migration. One theory to explain this is that their internal navigational system is malfunctioning.
Finally, range is a dynamic concept, and a species' range often changes, albeit slowly. Tufted Titmice and Northern Cardinals, for instance, live much further north than they did 100 years ago.
If you are fortunate enough to see a rare bird, you should probably report it to your local bird club, Rare Bird Alert, or Audubon chapter. Take careful notes about what you see, recording plumage, beak shape, eye color, and any other features that will aid in identification. Draw a sketch of the bird noting any distinctive characteristics. Also, try to take a photograph or video of the bird in action, and confirm your sighting with another knowledgeable birder. Your careful documentation of this bird will ensure that your report becomes part of the scientific record.