Re the significance of the chestnut collar, I seem to remember Kenn
Kaufman's account in the Audubon "master guide" indicating that
females can sometimes have a chestnut wash on the nape, as well as
some black on the underparts. It's too bad field guides don't routinely
indicate the source of diagnostic characters (personal observation
vs. primary lit. vs. taken-from-another-field-guide, etc.).

David Wright
dwright at u.washington.edu