April 14th, 2017
Several weeks ago Hawks Aloft staff made the trip to Monte Vista, Colorado for the Monte Vista Crane Festival. Upon their arrival they started to hear rumors of a Red-tailed Hawk haunting the edges of the wildlife refuge. But this was no ordinary Red-tailed; defying the colors that dominate the species, this was a largely white Red-tailed Hawk, with only the occasional rust or brown feather that birders might expect when it comes down to identifying such a bird.
This particular hawk—a leucistic one—isn’t an entirely common sight, and Hawks Aloft staff and volunteers were thrilled to spot it on their first day out. It is hard to get an accurate grasp on how common leucism is in birds, but Project FeederWatch, an extensive online database of bird species observed and reported by citizen scientists, has recorded only about 1,600 leucistic birds of any species out of 5.5 million distinct birds indicated. But what exactly is leucism? And why does it happen at all, albeit infrequently?
Leucism is a blanket term for abnormal plumage conditions caused by genetic mutations. This genetic inheritance prevents a pigment—melanin—from being carried and deposited in the bird’s plumage. This condition can end up looking like the Red-tailed Hawk spotted in Colorado, or it can also be displayed as white patches throughout the body, in places where they wouldn’t normally occur in a species. Sometimes the condition also manifests as an overall paler plumage in the bird, as if its color was diluted.
Leucism is quite different than albinism, another similar (and similarly unusual) condition in birds. Considered to be extremely rare in the wild, albinism is marked by a total lack of melanin. Leucism, notably, only impacts the bird’s feathers, while albinism is apparent in the feathers and elsewhere. For example, albino animals almost always sport red eyes, as well as pale pink or red skin, feet and bills. Leucistic birds usually have normally colored eyes, skin and feet; the condition of leucism only impacts the feathers.
Although it is quite exciting to see a leucistic bird in the wild, they do face certain challenges that make their lives difficult. These birds, without the protective camouflage that other animals have, become more vulnerable to predators. Additionally, plumage colors play an important role in courtship and mating; as such, many leucistic birds may be unable to find suitable mates. Last but not least, the dysfunctional melanin production in leucistic bird’s feathers may even make it harder for them to fly. Since melanin is an important structural component to feathers, birds lacking the proper amount of this pigment may have weaker feathers that are more prone to breaking and less able to insulate the body against cold and damp.
Leucism can be a great burden on the bird, however, it does remain rare. As such, when a birder spots a bird such as this, it allows for a moment of pause as we consider the great complexity of avian life, and the beautiful and observable variety among these amazing animals.
Maggie Grimason is senior editor and an educator at Hawks Aloft