Duck — extremely succulent and fatty bird (7)
I believe the answer is:
ostrich
'bird' is the definition.
(ostrich is a kind of bird)
'duck extremely succulent and fatty' is the wordplay.
'duck' becomes 'o' (resembles zero - 'duck' in cricket).
'extremely' means to remove the middle letters (only the extremes of the word are used).
'and' is a charade indicator (letters next to each other).
'fatty' becomes 'rich' (as in rich foods).
'succulent' with its middle removed is 'st'.
'o'+'st'+'rich'='OSTRICH'
(Other definitions for ostrich that I've seen before include "One refusing to face facts; flightless African bird" , "The head-in-the-sand bird" , "A bird for the shirt co." , "World's largest bird" , "Nut-burying type" .)