A change involving island enclosure for birds (6)
I believe the answer is:
aviary
'enclosure for birds' is the definition.
(I've seen this before)
'a change involving island' is the wordplay.
'change' becomes 'vary' ('vary' can be a synonym of 'change').
'involving' indicates putting letters inside.
'island' becomes 'i'.
'vary' going around 'i' is 'viary'.
'a'+'viary'='AVIARY'
(Other definitions for aviary that I've seen before include "Where flights are limited" , "Bird enclosure" , "Large birdcage" , "Collection of birds" , "Bird-house" .)