Peryton

The Peryton is said to have the head, neck, forelegs and antlers of a stag, combined with the plumage, wings and hindquarters of a large bird, although some interpretations portray the Peryton as a deer in all but coloration and bird's wings.
According to Borges, Perytons lived in Atlantis until an earthquake destroyed the civilization and the creatures escaped by flight. A Peryton casts the shadow of a man until it kills one during its lifetime, at which time it starts to cast its own shadow. A Sibyl once prophesied that the Perytons would lead to the downfall of Rome.
In Borges' original Spanish edition, the word is given as peritio so the presumptive Latin original would be peritius, which happens to be the Latin name of the fourth month on the ancient Macedonian calendar, (Peritios, moon of January). The connection of this, if any, to the peryton is unclear.