Thanks very much for this, Zac. I regularly see odd-looking, darker Red-Tails around the southern Champlain Valley in wintertime and couldn't really do much more than wonder about them. I'd also been seeing them for years on various winter birding trips to the area before I moved here 15 years ago. Now I know what to look for. (Although I do wish the eBird discussion had more pix to illustrate the text. At least there are links to other discussions, and hopefully photos, of these guys.) Jane (Shoreham)