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ZOO-ology: Mutations can make odd birds

By By Judie Farnsworth
Aug. 5, 2012 at 3:05 a.m.

Red-tailed hawk.

I recently received a picture of a peculiar black and white bird.

A few days later, I got a phone call about a similar bird. It looked like a grackle, but it was patchy with white. What was it?

Well, it was indeed a grackle, but why did it look like that?

And, why do some other animals sport rather strange looking colors for their species?

Several interesting conditions involving pigments can result in striking colors and patterns.

Decoding the findings of on-going studies is mind boggling, so in the interest of sanity, mine and possibly yours, a smaller amount of information will hopefully suffice.

The grackle in question may have been a pied or piebald leucistic (loo kis' tic) bird. This is a genetic mutation where, although the various pigment cells (chromatophores) are present, some haven't developed normally or may not be located in typical areas. The result can be a bizarre patchy, bleached or all-white appearance.

Many times, the color or pattern is there, but is just not as recognizable.

Animals/birds with abnormally all-white fur/feathers are usually referred to as just leucistic. They have melanin, but it shows in eye color, skin or pads of the feet.

For comparison, a more familiar, but different condition is albinism. It's a genetic mutation where there is a lack of black (melanin) pigment cells. The entire animal, skin, hair, even eyes are affected instead of only patches.

Albinos, although lacking melanin, may still have faint color from pigment cells other than melanin. In true albinos, the lack of melanin usually results in pink or red eyes, which are a reflection of blood vessels in the eyes.

Albino and leucistic mean the same thing - white. It's a matter of where, how and if color cells are deposited.

Birders sometimes see color oddities; a bleachy looking robin, a white hummingbird, a patchy hawk.

There is an opposite, called melanism, where an abnormal amount of the black pigment (melanin) is present. Color phases or morphs develop when reproductive partners have the same recessive genes.

The red-tail hawk has a dark morph called a Harlan's and a light morph called Krider's.

Typically, birds and animals with abnormal patterns or colors don't live as long, lacking the natural camouflage to avoid predators. In birds, white feathers are often weaker than dark ones and wear out more quickly. They also reflect the sun, which is problematic for birds that sunbathe for warmth.

Abnormal coloring can also make attracting a mate difficult. Some baby birds have spots of color that are a target for parents feeding them. Without a normal coloring, the bird might not be readily fed.

Check out the websites listed below for some great pictures, and the next time you're at the Texas Zoo, see if you can spot some of our peacocks that fit this topic.

Sources:

Red-tailed hawk photo courtesy of Jim & Deva Burns. jimburnsphotos.com

birding.about.com/od/identifyingbirds/a/leucism

birds.cornell.edu/pfw/.../Albinism_Leucism

wildlifeextra.com/go/news/ leucism

Judie Farnsworth is a longtime volunteer at the Texas Zoo specializing in educational programs.

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