Nice to see some discussion of this. When I saw the Gyrfalcon a week or so
ago, it caught and began feeding on what I presumed was a meadowlark. While
feeding, it was buzzed by another very similarly sized falcon. The other
falcon disappeared almost immediately, so I was unsure of what it was,
A nice analysis by Dave Leatherman. I'd also point out that part of what gives
Prairie Falcons a dark-armpitted look in flight, the contrastingly dark flanks,
is also quite apparent while perched. This is demonstrated well by Dave's
images; compare the even streaking/barring through the
Dave, thank you for your excellent comparison of markings, a fine discussion
and the two helpful photographs. If I may further add to your description, as
a falconer and someone who has worked with males and females of both species:
I've been told by several experienced raptor watchers who've
