Ferruginous Hawks (Buteo regalis) prefer open habitats such as grasslands. They're known for eating jackrabbits, which are available along Coleman Valley Road where these pictures were taken (on 19 December 2012).
There are several features to look for:
- large size (bigger than a Red-tailed Hawk)
- mostly white below (paler than most other hawks in this area)
- rufous coloration on the back, shoulders, and leg feathers (hence the name "ferruginous" which means "rusty")
- black markings at the "wrist" or bend of the wing
- wide gape (the corner of the mouth extends beyond the eye)
- white or gray tail
- wavy, rust-colored bars on the belly
Here are two pictures showing some of the wing patterning:
And a few more of the same bird perched high in a tree. Look for the rusty bars on the belly.
The bright light on the hawk's pale belly made photographing this bird a little challenging. Later I was intrigued to read this description in the Birds of North America account (Bechard and Schmutz 1995):
"White belly of light morph reflects sun and makes hawk highly visible even when roosting on ground. This could be an advantage for advertisement in a territorial or mating context in open landscape."
Note that there are two forms of Ferruginous Hawks, light morphs (shown above) and dark morphs. The dark morphs are much less common, making up 0-10% of populations. In November, a dark morph individual was observed in Petaluma (along Adobe Road), but I haven't heard if it's still around.