Kara C. Donohue and Alfred M. Dufty, Jr. wrote an excellent paper about using size measurements and weight to determine sex in Red-tailed Hawks, Sex determination of Red-tailed Hawks (Buteo jamaicensis calurus) using DNA analysis and morphometrics, J Field Ornithology, Vol 77, Issue 1, pp. 74-79.
This paper shows how hard it is to tell a Red-tail's sex. I would caution anyone who thinks they can quickly tell a Red-tails sex by simple observation to think twice before declaring the sexes of our two Cathedral fledglings.
Update: This note sparked a discussion between Donna Browne and John Blakeman about this year's fledglings sexes on Donna's blog, palemaleirregulars. My comments above were to start a discussion about the sex variations beyond just height. I think Donna and John are exploring this very well on her blog.