A libertine takes on domesticated bird (8)
I believe the answer is:
parakeet
'bird' is the definition.
(parakeet is a kind of bird)
'a libertine takes on domesticated' is the wordplay.
'libertine' becomes 'rake' (rake is a kind of libertine).
'takes on' is an insertion indicator (inserted letters are worn or taken on).
'domesticated' becomes 'pet' (I've seen this in other clues).
'a'+'rake'='arake'
'arake' going inside 'pet' is 'PARAKEET'.
(Other definitions for parakeet that I've seen before include "Bird popular as a pet" , "Brightly-coloured African bird" , "Flier" , "Tropical bird" , "Small long-tailed parrot" .)