Cuckoo can oust birds (7)
I believe the answer is:
toucans
'birds' is the definition.
(toucan is a kind of bird)
'cuckoo can oust' is the wordplay.
'cuckoo' indicates anagramming the letters (I've seen this in other clues).
'can'+'oust'='canoust'
'canoust' is an anagram of 'TOUCANS'.
(Other definitions for toucans that I've seen before include "they come with big bills" , "Brilliantly coloured birds of tropical America" , "Brilliantly coloured birds with very large beaks" , "Flyers" .)