Animal in fewer numbers (3)
I believe the answer is:
ewe
'animal' is the definition.
(I've seen this before)
'in fewer numbers' is the wordplay.
'in' indicates a hidden word.
'EWE' can be found hidden inside 'fewer numbers'.
(Other definitions for ewe that I've seen before include "Source of milk" , "One needing pastoral care" , "A palindromic sheep" , "Dam of a sheep" , "Partner to ram" .)