Bird that was finally caught in ditch (4)
I believe the answer is:
moat
'ditch' is the definition.
(I know that moat is a type of trench)
'bird that was finally caught' is the wordplay.
I cannot really see how this works, but
'bird' could be 'moa' (extinct flightless bird of New Zealand) and 'moa' is found in the answer.
'finally caught' could be 't' (final letter of 'caught') and 't' is found in the answer.
This accounts for all the letters.
This explanation may well be incorrect...
'in' acts as a link.
Can you help me to learn more?
(Other definitions for moat that I've seen before include "Last ditch defence?" , "Protective ditch" , "Water-filled trench around a castle" , "Water around castle" , "A deep water-filled ditch around a castle" .)