Five hundred automatic rat and stoat traps have been laid around a remote area of Fiordland to help protect 150 South Island robins, or toutouwai, translocated a fortnight ago.
The last of the traps were laid out last Friday on a 2600ha "island" in the area surrounding Martins Bay, in the lower Hollyford Valley, where the Hollyford Conservation Trust has been working for five years to control predators.
The area is only accessible by air, or three to four days' walk.
Sam Gibson, of technology company Goodnature, said single-use traps set over the same area would require "hundreds of hours of maintenance over a year".
The pests were attracted into the trap by a long-life rat lure, which remained fresh for six months.
As they brushed past the sensitive leaf-trigger, a CO2 pressurised piston struck the pest's head, killing it instantly, then retracting on a light spring.
The dead pest fell to the ground and the trap automatically reset.
Hollyford Conservation Trust chairman Rod Andersen said the pest control work to date had made a "real difference" - predators were now consistently tracking at below 5 per cent.
The land the trust protects includes an important dune system home to thousands of nesting seabirds including the rare Fiordland crested penguin, a lagoon, wetlands, mixed beech and podocarp forests and many native bird species, including the kākā and kea.
"In the four breeding seasons since we've been trapping here, we've seen an incredible increase in these species in the area," Andersen said.
"The new [trap] network will really help to achieve our vision of abundant native wildlife in the area, safe from predation."