No way to really tell! The only way one can tell the difference from a distance is if it were to just be huge beyond no possibility of it being a male and even then, who really knows, it is still an educated guess. There are so many size variations in red-tails, even when we trap them the only sure fire way is to have them DNA tested. I wouldn't just enjoy the view, I can't keep my eyes on the road most of the time because I am scanning trees, power poles, etc along the highways. LOL