Omnivorous mammal in Channel Islands eating grass (5)
I believe the answer is:
coati
'omnivorous mammal' is the definition.
(I've seen this in another clue)
'channel islands eating grass' is the wordplay.
'channel islands' becomes 'CI'.
'eating' means one lot of letters goes inside another.
'grass' becomes 'oat' (I've seen this in other clues).
'ci' going around 'oat' is 'COATI'.
'in' acts as a link.
(Other definitions for coati that I've seen before include "South American animal" , "S. and Central American raccoon-like animal" , "Tropical animal" , "wild animal" , "American mammal related to raccoon" .)