Tower guard loses fine bird (3-5)
I believe the answer is:
bee-eater
'bird' is the definition.
(bee eater is a kind of bird)
'tower guard loses fine' is the wordplay.
'tower guard' becomes 'beefeater' (I've seen this before).
'loses' suggests deleting specific letters.
'fine' becomes 'f' (abbreviation e.g. condition of old coins, books).
'beefeater' with 'f' taken out is 'BEE-EATER'.
(Other definitions for bee-eater that I've seen before include "Bright avian insectivore" , "Insect-consuming bird" , "Bright bird" , "Insectivorous bird" .)