Song about head of zoo working in one of the US states (7)
I believe the answer is:
arizona
'one of the us states' is the definition.
(Arizona is a US state)
'song about head of zoo working' is the wordplay.
'song' becomes 'aria' (aria is a kind of song).
'about' is an insertion indicator.
'head of' suggests taking the first letters.
'working' becomes 'on' (on can mean working or activated).
The first letter of 'zoo' is 'z'.
'z'+'on'='zon'
'aria' placed around 'zon' is 'ARIZONA'.
'in' is the link.
(Other definitions for arizona that I've seen before include "US state, home to the Grand Canyon" , "Site of Grand Canyon" , "American state, capital Phoneix" , "American state, capital Phoenix" , "State of southwest USA" .)