partial leucistic red-tailed hawk
(the following picture was added after the original post)
Thanks to a tip from Larry “the raptor magnet” Broderick of West County Hawk Watch, I was able to see another amazing bird yesterday. Leucism is a recessive gene defect that affects the pigment cells’ development in some parts or an entire animal, causing either the whole animal or some of its feathers, fur, hair or skin to be white. It’s similar to (but different than) albinism, which only affects the melanin pigment cells. The effect can be really cool to see, as it is in this red-tailed hawk that I photographed in Sonoma County yesterday.
Viewing the bird from the front or from underneath, it’s difficult to tell that it has different plumage than a typical red-tailed hawk, though on close inspection of it flying from underneath, you can see a couple of flight feathers that are all white. From a rear or top-down view while flying, it is obvious (and not easy to photograph!! I forgot to bring my jet pack yesterday).
A bald eagle that I photographed last winter also has leucism, and it was striking. See those posts with pictures again here.
Another local raptor expert, George Eade, photographed an almost completely white red-tailed hawk here in the Bay Area a few years ago, his pictures can be seen here. The bird and the pictures are absolutely amazing.