Fourteen Doc rangers and volunteers enticed the first flock of 30 yellowhead birds from the Dart Valley, near Glenorchy, into pre-staged nets by recorded mohua song.
Up to 60 birds will be caught with mist nets and flown from the valley to the remote Secretary Island, part of the Fiordland National Park and at the entrance to Doubtful Sound.
Doc Wakatipu biodiversity manager Barry Lawrence said the formerly-threatened mohua population in the Dart Valley had strengthened to more than an estimated 3000 and would become the nucleus of a new breeding colony in Fiordland.
"The Dart's mohua population has gained sufficient size and genetic diversity to allow us to populate an area like Secretary Island on a large scale."
Mr Lawrence credited an aerial drop of pest poison 1080 over 56sq km in October 2006 for the recovery of the species.
"Quite simply, areas where rats were controlled with aerial 1080 are teaming with life. The uncontrolled areas have no birds at all - mohua have become locally extinct."
University of Otago associate professor of zoology Ian Jamieson said the faculty's collaborative research with Doc showed Dart mohua had the greatest genetic diversity of any mohua population.
"Translocating birds from the Dart to Secretary Island will not only reduce their risk from predators but will ensure that the newly established population will have the maximum genetic diversity possible.
"Past island transfers have involved small numbers of birds. This can lead to low genetic variability resulting in poor reproduction and lower disease resistance. When returned to mainland sites, individuals can struggle to compete for food and fall prey to predators."
Mr Lawrence said Secretary Island was rat-free and the focus of intensive deer and stoat eradication.
"Now lush with silver beech, the habitat for mohuas' favourite foods, beetles and caterpillars, the island is an ideal place to build up numbers for a return to the mainland."
