I took a peak at the photos posted here from September in Larimer county. There is no obvious difference between the two birds, other than the tails. The bird near Casper “appears” to have a somewhat significantly longer tail (how about all that scientific jargon, eh). As you all know, that can be due to angle, extension, etc. The wind was blowing the tail straight in my photos. Also, the bird could have been finishing a molt 11 days ago. The subspecies monachus molts into September (Pyle 1997). That could be a great indication of this bird’s origin. Cool stuff, bird homies.