Small quarry devoured by outsize birds (7)
I believe the answer is:
ospreys
'birds' is the definition.
(osprey is a type of bird)
'small quarry devoured by outsize' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'quarry' becomes 'prey' (synonyms).
'devoured by' is an insertion indicator.
'outsize' becomes 'os'.
's'+'prey'='sprey'
'sprey' going within 'os' is 'OSPREYS'.
(Other definitions for ospreys that I've seen before include "Preys so close to fishing eagles" , "Large birds of prey and a Welsh rugby team" , "Sea eagles" , "Large hawks, they feed on fish" , "Fliers" .)