A Whiter Shade of Pale

Despite the colder temperatures and snow of late across most of Colorado, the birds have definitely been signaling that spring is on its way. In fact, astronomically, the spring equinox happens next month (this year it’s March 20th). When you think of spring, what comes to mind? For some people, me included, one of the most common indicators of spring is the reappearance of the American robin in your backyard.

Partially leucistic or "piebald" American robin in northern Colorado. Photo by Jamie Simo.
Partially leucistic or “piebald” American robin in northern Colorado. Photo by Jamie Simo.

The American robin (Turdus migratorius) is one of the most ubiquitous song birds in North America. While it’s commonly believed that they migrate south in the fall (and some do, particularly those in the upper reaches of Canada and the U.S.), a lot of robins actually spend their winters where they spend their summers. They just might not be as visible because they’re clustered together in trees eating berries instead of on the ground foraging for worms.

A few weeks ago, I noticed that the robins had returned. Spurred on by hormones, their winter flocks were breaking up and they were starting to lay claim to spring breeding grounds. One day, I was watching a couple of robins on the roof of my neighbor’s gazebo when I did a double take; one of the robins had a partially white head! What was going on?

Color in animals is dictated by the amount of pigments in the cells of their skin, hair/fur, scales, or feathers. One of those pigments is called “melanin.” The darker the animal’s features are, the more melanin is being produced. Albinism is the total absence of melanin and results in an all-over white or pale pink coloring (the pink is the blood vessels showing through) and, often, red eyes. Last summer, I visited the Colorado Gators Reptile Park in Mosca, Colorado, and saw several albino alligators, but this robin clearly wasn’t like them; Aside from his head, the robin was a normally colored bird. What else could explain his unusual look?

Albino alligator at the Colorado Gators Reptile Park in Mosca, Colorado. Photo by Jamie Simo.
Albino alligator at the Colorado Gators Reptile Park in Mosca, Colorado. The green is from algae. Photo by Jamie Simo.

Similar to albinism, leucism also involves a reduction in color in the skin, hair/fur, etc. However, scientists believe that leucism differs in that pigments (melanin as well as other pigments) are produced, but not deposited in particular areas. This can result in an animal that’s completely white with normal-colored eyes, one that is a muted shade of its usual coloring, or even one where only patches of the animal are white (called piebald). The latter is probably the category my robin fits into. Piebald is a common color pattern in domestic animals such as horses, dogs, cats, and cows.

Leucism, like albinism, can make an animal more susceptible to predators by reducing its natural camouflage. In addition, because melanin provides structural support to feathers (hence why the wing tips on even white birds are typically black), an albino or leucistic bird where the leucism affects the wings, may experience more feather wear. This, in turn, could cause problems during migration. It’s also been theorized that albinism and leucism could cause problems in animals, such as some birds, that rely on color for mating displays, or that it may cause problems trapping heat in cold climates because paler colors reflect more solar radiation than darker colors.

So far there doesn’t seem to be much of an impact on my leucistic robin neighbor, but the real test will be this upcoming breeding season.

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s