Some fascinating stuff over at the British Museum website. This about “human owls”:
Aztecs had a strong belief in fate; the day in which a person was born had a particular significance. People born on 1 Rain, whether noble or commoner, man or woman, had a tendency to become a tlacatecolotl(human owl). These creatures could cause sickness and even kill people.
The day you were born could mark you as a “creature.”