A big red-tail has no problem at all completely toting off a good-sized chicken, I've seen 'em do it before. Foxes will usually carry a chicken off with no trace before stopping to eat it in a safe place, too. Chickens might as well have DORITOS wrote on their backs, because they're the tater chips of the animal world. I kept chickens for many years, and I've lost them to foxes, yotes, bobcats, hawks, owls, skunks, dogs, weasels, possums, coons, wharf rats, minks, and lord knows what else. Your rooster was probably either terrified of whatever got the hen and ran off, or was following the critter trying to protect the hen, one or the other.