Hear large mammal howl (4)
I believe the answer is:
wail
'howl' is the definition.
('wail' can be a synonym of 'howl')
'hear large mammal' is the wordplay.
'hear' indicates a 'sounds like' (homophone) clue.
'large mammal' becomes 'whale' (I've seen this before).
'whale' sounds like 'WAIL'.
(Other definitions for wail that I've seen before include "Whimper" , "Lament loudly" , "Long cry, sounds like cetacean" , "Lament noisily" , "Cry piteously" .)