I went all the way to North Dakota and deserve to have seen a Ferruginous, don't you think? I had my life Swainson's Hawk in Cape May years ago and a textbook-looking one that Bill of the Birds showed us on my birthday on the first day of the Potholes and Prairie Festival.
Then, we surprised this hawk the following day in the hills of the Coteau Region. Tell me what makes this a Swainson's... maybe I'll take your word for it.
As an aside: I'd thought separating Eastern hawks was difficult. Pfft!
The Swainson's has 3 age classes and is polymorphic (whatever the heck that means!) The Ferruginous has 2 ages classes and is also polymorphic. (I think!)