Pigeons initially disconcert rabbit (7)
I believe the answer is:
prattle
'rabbit' is the definition.
(both can mean to talk excessively)
'pigeons initially disconcert' is the wordplay.
'initially' suggests taking the first letters.
'disconcert' becomes 'rattle' (I've seen this before).
The initial letter of 'pigeons' is 'p'.
'p'+'rattle'='PRATTLE'
(Other definitions for prattle that I've seen before include "Inconsequential chatter" , "rabbit" , "Be vapidly garrulous" , "Blether" , "Idle talk" .)