Clue: Spies seizing port with tip-off for treecreepers (7)
Answer: CERTHIA
Explanation: Definition: treecreepers
**CIA **(Central Intelligence Agency, so "spies") *seizing* (p)**ERTH** (Australian "port" with its *tip off*) *[EDIT – may be (b)ERTH?]* 
*Certhia is the genus of birds that includes treecreepers (not in any of my three go-to dictionaries, but found on Wikipedia)