Dodos
(Another definition for morons that I've seen is " fools".)
'dodos' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for asses that I've seen before include "Animals of horse family" , "Idiots" , "More than one fool" , "Dolts" , "Fools; beasts of burden" .)