No pictures with this one. As many times as I have tried, I have not been able to get any good shots of the hawks I see through my office window. We have one I call the "resident red tail". Lately I've seen two separate hawks. One is a beautiful hawk with dark wing-tips. And the other is obviously either molting or has been in a bit of a tussle as it is missing both wing and tail feathers. (I saw them both today -- together!)
I've also gotten pictures of a hawk near my home with some primaries missing (see below). Both of these hawks have gotten me to thinking about molting in hawks. So tonight I did a bit of research on the web. From several sites, I read about the "first molt". Juvenile hawks wear their feathers for a whole year (at least) before their first molt. Interestingly, the juvenile feathers are longer than the adult feathers, so a juvenile hawk will appear to be larger than an adult -- though it's only in the length of the feathers, not weight or strength of the bird. Read about that and the order of molting in this Q&A found here.
This interesting article by "The Modern Apprentice" details the different types of feathers on a hawk with pictures!
From the Illinois Raptor Center's Learning Pages, I learned that the feathers look like little paint brushes as they begin to grow. Look at some great pictures of a juvenile hawk undergoing it's first moult. This page also gave me the first hint of what I was really looking for -- when do hawks go into molt?
Finally, I found a research paper entitled "Aging, Sexing and Molt" which explains that while most birds molt over the summer, some will have a partial molt before the breeding season, or before migration. Hawks migrate in the spring and fall -- so maybe these birds are molting either before breeding, or in preparation for the spring migration.