When in choir dress, a Latin-rite cardinal wears scarlet garments — the blood-like red symbolizes a cardinal's willingness to die for his faith. Excluding the rochet — which is always white — the scarlet garments include the cassock, mozzetta, and biretta (over the usual scarlet zucchetto). The biretta of a cardinal is distinctive not merely for its scarlet color, but also for the fact that it does not have a pompon or tassel on the top as do the birettas of other prelates. Until the 1460s, it was customary for cardinals to wear a violet or blue cape unless granted the privilege of wearing red when acting on papal business. His normal-wear cassock is black but has scarlet piping and a scarlet fascia (sash). Occasionally, a cardinal wears a scarlet ferraiolo which is a cape worn over the shoulders, tied at the neck in a bow by narrow strips of cloth in the front, without any 'trim' or piping on it. It is because of <answer>the scarlet color of cardinals' vesture</answer> that the bird of the same name has become known as such.[citation needed]
The Cardinal bird was named as such because of what in relation to Cardinals of the church?
the scarlet color of cardinals' vesture