Again end up getting duck (5)
I believe the answer is:
eider
'duck' is the definition.
(eider is a type of duck)
'again end up' is the wordplay.
'again' becomes 're' (prefix meaning 'again').
'end' becomes 'die'.
'up' shows that the letters should be reversed in order (in down clue: letters go upwards).
're'+'die'='redie'
'redie' reversed gives 'EIDER'.
'getting' acts as a link.
(Other definitions for eider that I've seen before include "Downy sea duck" , "Duck from which down is obtained" , "I've noted down" , "Sea duck with soft down" , "Sea bird" .)