The Department of Conservation has brought in specialist equipment after a possible rat sighting on Hauturu/Little Barrier Island.
The island is a pest-free nature reserve and home to 40 species of endangered native birds, lizards and wetapunga.
A DoC ranger was looking under a shelter on Wednesday when they saw something moving that may have been a rat.
"The area under the shelter was very dark," says DoC Auckland inner islands operations manager Keith Gell.
"The ranger caught a brief glimpse of something retreating into the darkness.
"His initial thought was that it could have been a rat or a robin, a bird that spends a lot of time on the ground eating insects."
A rodent-tracking tunnel, which uses ink to track rat footprints, was checked and no rat tracks were found - but it is believed the ink may have been too dry to work.
Upon inspection with a magnifying glass, the ranger believes small hairs may be present on the card.
The ink card has now been flown to the mainland for specialist testing while a conservation rodent-detector dog was flown out to the island via helicopter, which also didn't find any traces of rodent.
In the meantime, a network of devices has been set up to catch the possible rat including three motion sensor cameras, tracking tunnels with fresh ink cards, chew cards that record teeth marks and traps.
A ranger will remain on the island to monitor the cameras and other devices for a week.