A bird elephants should be wary of! (3)
I believe the answer is:
roc
'a bird' is the definition.
(mythological bird of prey)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for roc that I've seen before include "Gigantic bird of eastern legend - cor!" , "Legendary thing" , "Legendary flier" , "Big bird" , "Fabulous giant bird of Eastern legend" .)