Some species

of birds are furnished additionally with spurs,
but no bird with crooked talons is found so provided. The birds with
talons are among those that fly well, but those that have spurs are
among the heavy-bodied.

Again, some birds have a crest. As a general rule the crest sticks
up, and is composed of feathers only; but the crest of the barn-door
cock is exceptional in kind, for, whereas it is not just exactly
flesh, at the same time it is not easy to say what else it is.