Brawler disturbed small songbird (7)
I believe the answer is:
warbler
'small songbird' is the definition.
(I've seen this before)
'brawler disturbed' is the wordplay.
'disturbed' indicates anagramming the letters (the order of letters is disturbed).
'brawler' is an anagram of 'WARBLER'.
(Other definitions for warbler that I've seen before include "songster" , "18's [BIRD]" , "A small songbird or similar singer" , "XWD SETTER" .)