Quail say, following first of wrens (5)
I believe the answer is:
waver
'quail' is the definition.
(thesaurus)
'say following first of wrens' is the wordplay.
'say' becomes 'aver' ('aver' can be a synonym of 'say').
'following' is a charade indicator (letters next to each other).
'first of' suggests taking the first letters.
The first letter of 'wrens' is 'w'.
'aver' after 'w' is 'WAVER'.
(Other definitions for waver that I've seen before include "Vacillate" , "One making signal" , "hold back" , "someone gesticulating wildly" , "Begin to weaken" .)