Birds to illustrate, perched on plastic rest (6)
I believe the answer is:
egrets
'birds' is the definition.
(egret is a kind of bird)
'perched on plastic rest' is the wordplay.
'perched on' becomes 'eg' (I can't justify this - if you can you should believe this answer much more).
'plastic' indicates an anagram (plastic can mean easily moulded).
'rest' with letters rearranged gives 'rets'.
'eg'+'rets'='EGRETS'
'to illustrate' acts as a link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for egrets that I've seen before include "waders" , "Kind of herons with long white feathers" , "White wading birds" , "creatures" , "Fliers" .)