Definitely a raptor, but as a silhouette the dimension and proportions of the bird become foreshortened, hiding the full form.
I'd say an eagle, though, based on the wing shape -- the "fingers" are typical of eagles and vultures -- but the shape of the head has been softened and rounded (maybe it was a view from above, looking down onto the top of the bird's head). I'll go with "abstract eagle." It's kind of a nice, mysterious figure.
I'm only on p.63 of the book thusfar (arrived yesterday), but really enjoying the read.