Quetz is part of a bird-family that is quite ancient and was believed to be extinct. They were called Harpies, after the half-human/half-bird creatures in Roman and Greek mythology because of the bird's human-like features. Parvati was able to save one egg which hatched into Quetz, for who she has taken care of, later being joined by Zonas with whom she really connected on a deep level, despite their language barrier.
Being a bird, Quetz doesn't have any way of talking to the humans. She however can express human emotions through her face. She can understand them and they can understand her, which causes for Quetz to be able to form a connection with someone, best displayed in Zonas. She is an energetic bird who likes to sing and only gets sad when people are really mean to her.
The Harpies are said to be a protective charm to their owner. When their owner is in a dire situation, they will get out of it unscratched due to the protection of the Harpy, as if it were manipulating how the events would go normally. However this is all believed to be this way and never has been confirmed to be real.