While I was driving in a residential area in Fredericksburg recently, a dark colored hawk flew in front of my car not far above the top of the tree canopy. Instantly I realized that this was not a bird I had seen before; my first thought was that it was a melanistic Red-shouldered Hawk, even though I have never seen a melanistic Red-shouldered Hawk before. What I saw was a medium- sized hawk with the profile of a red-shoulder. A normal colored red-shoulder plumage would have an orange barred breast, dark brown to gray blotchy-patterned head, wings and tail, the latter also barred. Its red shoulder patch would not likely be discernable.
The plumage I saw on this bird included a dark gray head, body and tail. The wings were checkered with gray and white and its tail was not barred; no indication of any orange or rufous coloration was visible. Red-shouldered Hawks are woodland birds that have adapted to urban woodland habitats, so this bird was in the right habitat for a Red-shouldered Hawk. Red-tailed Hawks are more open country birds and not likely to be in the center of an urban, residential woodlands setting. The only other possibility was a Zone-tailed Hawk, a raptor that looks like a Turkey Vulture with white bars in its tail. The profile of the bird in question did not match a vulture’s profile with or without the bars in its tail.
At first chance, I went to my bird books to see if any photos or drawings matched the bird I had seen. Red-tailed hawks are well known to have dark-morphed plumages; they even have their own name, Harlan’s Hawk; however, I instinctively knew it was not this hawk. Interestingly, none of my bird books profiled a melanistic Red-shouldered Hawk. My next information source was the internet. If it exists, it will likely be on the internet. My search was successful giving me several choices to consider from many photographs of melanistic Red-shouldered Hawks. I decided my first impression had been correct.
Now, let us consider “melanistic” birds. Melanistic birds have an unusually high amount of the pigment melanin. Birds with unusually low amounts of the melanin pigment are referred to as being “leucistic.” Birds and mammals that have no melanin pigment are called “albinos.” The latter is a recessive genetic character, and the individuals often also have malfunctions in body chemistry. So, what is the difference between partial albinism and “leucistic” individuals? To the layman, there is no difference; the geneticist may have other explanations concerning differences.
In contrast to the problems associated with pure albino animals having weak body chemistry, melanistic animals have stronger associated body chemistry. For, example, increased melanin pigment strengthens the structure of feathers. It is interesting that many white birds such as White Pelicans, Snow Geese, and Whooping Cranes, have black primary feathers in their wings indicating the strength these feathers must have in order to bear the brunt of the action in propelling these birds through air currents. Another advantage that melanin adds is that the darker plumages allow the individuals to hide or blend into the background for safety, or possibly affording an advantage in hunting.
After many years of observing and studying nature, I am fascinated to discover the many subtle differences in plumages, body chemistry, behavioral habits, and other biological traits that factor in concerning why some birds survive and others go extinct. The key to survival often hinges on animals (birds included) being able to adapt to changes in climate, habitat, physiology and competition. Observing a bird with an unusual plumage can lead to interesting discoveries, if you are willing to let your inquisitiveness guide you in learning more about nature.