Execute rabbits and birds (6)
I believe the answer is:
dodoes
'birds' is the definition.
(dodo is a kind of bird)
'execute rabbits' is the wordplay.
'execute' becomes 'do' (synonyms).
'rabbits' becomes 'does' (I can't explain this - if you can you should give a lot more credence to this answer).
'do'+'does'='DODOES'
'and' is the link.
Can you help me to learn more?
(Other definitions for dodoes that I've seen before include "Old-fashioned types" , "people with little intelligence" .)