Crests formerly seen in parrots (6)
I believe the answer is:
apexes
'crests' is the definition.
The definition and answer can be both locations as well as being plural nouns.
Perhaps you can see a link between them that I don't see?
'formerly seen in parrots' is the wordplay.
'formerly' becomes 'ex' (prefix meaning former or onetime).
'seen in' is an insertion indicator.
'parrots' becomes 'apes' (I've seen this before).
'ex' put inside 'apes' is 'APEXES'.
Can you help me to learn more?
(Other definitions for apexes that I've seen before include "they're the tops!" , "Tips as of triangles" , "Summits, top points" , "Peaks, highest points" , "Tips or highest points" .)