That's an awful lot of birdsong on island first (8)
I believe the answer is:
trillion
'that's an awful lot' is the definition.
(large number)
'birdsong on island first' is the wordplay.
'birdsong' becomes 'trill' (I've seen this before).
'island' becomes 'i' (geographical abbreviation).
'first' says to put letters next to each other.
'on' put after 'i' is 'ion'.
'trill'+'ion'='TRILLION'
'of' acts as a link.
(Other definitions for trillion that I've seen before include "A great number" , "10,0003" , "1,000,000,000,000" , "enormous figure" , "A million multiplied by twice itself" .)