well we share visas with them. if you're an australian citizen then you're free to enter new zealand at any time. an australian passport basically doubles as a new zealand one and vice versa
hence why so many kiwis move to australia + we cant stop them sadly
the aussies stealing kiwi icon theme stems from the fact that people like russell crowe, keith urban + tonnes of new zealand sportsman that were born or lived in nz eventually moved to australia and claim to be australian.
hell we even stole their air force!(nz retired a lot of their airforce in the early 2000's so most of the pilots moved to australia and now work for us :icon_chee)