Going round by way of American railway? It's for the birds (6)
I believe the answer is:
aviary
'for the birds' is the definition.
(I've seen this in another clue)
'going round by way of american railway?' is the wordplay.
'going round' is an insertion indicator (some letters go around others).
'by way of' becomes 'via' (I've seen this in another clue).
'american' becomes 'a' (common abbreviation - e.g. in organisation names).
'railway?' becomes 'ry' (abbreviation for railway).
'a'+'ry'='ary'
'via' placed within 'ary' is 'AVIARY'.
'it's' acts as a link.
(Other definitions for aviary that I've seen before include "Building for keeping birds" , "Large birdcage" , "House for birds" , "Its inhabitants probably like flying" , "Large cage for birds" .)