Unexpectedly greets birds (6)
I believe the answer is:
egrets
'birds' is the definition.
(egret is a kind of bird)
'unexpectedly greets' is the wordplay.
'unexpectedly' is an anagram indicator.
'greets' is an anagram of 'EGRETS'.
(Other definitions for egrets that I've seen before include "waders" , "Greets like fishing eagles" , "Kind of herons with long white feathers" , "Fliers" , "Greets like certain herons" .)