It was the first GPS-tracked, long distance flight record of an Australasian harrier that the Department of Conservation (DOC) has documented.
The adult male left Whangamarino Wetland on 26 September, cruising at heights of 300m across the Cook Strait, before arriving in Middlemarch on October 7.
DOC said it was trying to better understand how this bird of prey interacted with threatened native bird species and how they used the environment.
Kāhu prey on small to medium-sized birds and mammals, insects, lizards and frogs, including critically endangered species like Australasian bittern/matuku-hūrepo and black-fronted tern/tarapirohe, and also scavenge road-kill.
Technical advisor Thomas Emmitt said they did not know the scale of kāhu's impact on threatened species and the GPS tracking recorded more detailed movements than previous studies.
"This research will help us understand whether we need to further protect these species from kāhu as part of wider conservation efforts," Emmitt said.
"By tracking harriers, we hope to understand how much time they spend foraging around places where vulnerable native species live compared with farmland or other areas, and whether it's just individual birds that pose a threat or kāhu more widely."
Kāhu are a common native bird that are known to disperse over large areas and DOC wanted to find out whether they were going into new territories.
"We've also seen a young female fly 150km between the St James Conservation Area and Hororata in Canterbury three times in just over a month. She seems to have settled in Hororata for now."
The early results showed some tagged kāhu were sticking to one area with criss-cross flight paths, he said.
Kāhu are partially protected under the Wildlife Act, but it is legal to control them to protect fully protected wildlife and DOC has controlled them to protect kakī/black stilt in the Tasman Valley and tara iti/NZ fairy tern in Northland.
