Bird sound from a hundred and two ducks (3)
I believe the answer is:
coo
'bird sound' is the definition.
'from a hundred and two ducks' is the wordplay.
'two ducks' means two substitutions for 'duck'.
'from' indicates anagramming the letters (from the letters).
'a hundred' becomes 'c' (roman numeral).
'and' means one lot of letters go next to another (I've seen this in other clues).
'duck' becomes 'o'.
'duck' becomes 'o'.
'c' put after 'o' is 'oc'.
'oc' is an anagram of 'co'.
'co'+'o'='COO'
(Other definitions for coo that I've seen before include "Murmur, speak softly" , "Sound made by dove" , "Bill and I go together" , "Make loving sounds -bill and . . ." , "Breathe" .)