In "The Nun's Priest's Tale," why is Chanticleer a round character in Chaucer's The Canterbury Tales?

A round character is defined as a character that is
neither purely good nor purely evil. A round character should have both flaws and
virtues that are evident.

A the beginning of the tale,
Chanticleer is praised for his attractiveness and excellent crowing abilities. These
would both be positive qualities. Chanticleer's worry in his dream also indicates that
he is able to feel, and to have concern. Chanticleer also expresses love towards
Pertelote.

Chanticleer's flaw is his vanity. He is wooed by
the fox's flattery enough to be captured. He loves to be flattered. He learned his
lesson by the end of the tale, though, when he smartly escapes the fox's
jaws.