Island creature, flightless bird, caught between both sides (5)
I believe the answer is:
lemur
'island creature' is the definition.
'lemur' can be an answer for 'creature' (lemur is a kind of animal). I am not sure about the 'island' bit.
'flightless bird caught between both sides' is the wordplay.
'flightless bird' becomes 'emu' (emus are flightless birds).
'caught between' is an insertion indicator (I've seen this in other clues).
'both sides' becomes 'lr' (abbreviation for left and right).
'emu' inserted within 'lr' is 'LEMUR'.
Can you help me to learn more?
(Other definitions for lemur that I've seen before include "Arboreal animal" , "Arboreal mammal common to Madagascar" , "Bushy-tailed primate" , "Monkey-like aniaml of Madagascar" , "Monkey-like creature of Madagascar" .)