Call volunteers close to Mull to save island animal (8)
I believe the answer is:
ringtail
'animal' is the definition.
(ringtail is a kind of animal)
'call volunteers close to mull to save island' is the wordplay.
'call' becomes 'ring' (telephone call).
'volunteers' becomes 'TA' (abbreviation for Territorial Army).
'close to' suggests the final letters (the 'close' to the word).
'to save' is an insertion indicator.
'island' becomes 'i' (geographical abbreviation).
The last letter of 'mull' is 'l'.
'ta'+'l'='tal'
'tal' enclosing 'i' is 'tail'.
'ring'+'tail'='RINGTAIL'
(Other definitions for ringtail that I've seen before include "Type of cat" , "Possum" , "Sleepwalker" , "creature" , "Sort of cat" .)