Linnets disturbed by good little bird (8)
I believe the answer is:
'little bird' is the definition.
(I've seen this before)
'linnets disturbed by good' is the wordplay.
'disturbed' indicates anagramming the letters (the order of letters is disturbed).
'by' is a charade indicator (letters next to each other).
'good' becomes 'g' (abbreviation).
'linnets' with letters rearranged gives 'nestlin'.
(Other definitions for nestling that I've seen before include "Young bird not yet fledged" , "in a huddle" , "Baby bird" , "Sitting snugly" , "Little bird" .)