Mac,
I'm not doubting your comment that there are wild ferrets in New Zealand.
 They certainly shipped enough over there and let them loose.  The
referrences I have though do call that to question.
 
"While ferret-like animals are found, especially in the region of Pukepuke
Lagoon, it is felt by many that these animals are actually polecats.  Dr. De
Vos and his colleagues, in their study of ferrets in this ecosystem, list
domestic ferrets as an 'unsuccessful introduction.'  Eventually stoats,
weasels and polecats were imported to replace them." - "1990 Information
Manual" W.B. Phillips; F. Shimbo; CDFA
 
Anyone from New Zealand out there who might know for sure?
 
Dick B.
[Posted in FML issue 1003]