Bird island near the bottom of the cliff (5)
I believe the answer is:
finch
'bird' is the definition.
(I know that finch is a type of oscine)
'island near the bottom of the cliff' is the wordplay.
'island' becomes 'inch' (inch can mean a small island).
'near' says to put letters next to each other (I've seen this in other clues).
'the bottom of' suggests the final letters.
The last letter of 'cliff' is 'f'.
'inch' after 'f' is 'FINCH'.
(Other definitions for finch that I've seen before include "Seed-eating songbird" , "Type of bird" , "Songbird such as a canary" , "Peter - - , film actor; bird" , "Singer" .)