Plume sources (6)
I believe the answer is:
egrets
'plume sources' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for egrets that I've seen before include "Greets in way of certain herons (" , "Greets like certain herons" , "Kind of herons with long white feathers" , "White wading birds" , "Fliers" .)