Last rat standing

A nearly six-month hunt for a lone Norway rat on Te Motutapu a Taikehu (Motutapu) has finally ended. 

The offender was first spotted in late April, on the previously pest-free island in the Hauraki Gulf/Tīkapa Moana. Ultimately, a network of around 50 cameras was the key tool that led to the predator’s demise.

While it is unknown how the rat arrived at its holiday destination, the Department of Conservation (DOC) says Aucklanders play a major role in keeping the island pest-free. “It could have stowed away in a boat, gear or bag, or potentially swam or drifted on debris from the mainland – Norway rats can swim up to 3 km,” said Kat Lane, DOC Inner Hauraki Gulf Islands Operations Manager.

DOC with support from Ngāi Tai Ki Tāmaki and Auckland Council tried multiple methods to catch the rat. The incident team used a variety of trap types and lures such as peanut butter, rat bedding and rat recordings, but the rat did not interact with any of these human-made devices – illustrating the real challenge in keeping valuable islands and areas pest-free.

Two new thermal imaging cameras, named DOC AI CAM and developed by the Cacophony Project, were a key part of the eradication. 

“We used a combination of standard trail cameras and AI cameras that gave us important and surprising information about the rat’s behaviour, routes and favourite locations,” said DOC Island Biosecurity Advisor Claire Warren. 

“The cameras revealed that the rat travelled from a suspected nest site to McKenzie Bay on Rangitoto Island, around 5.8 km away, which is much further than we ever expected. 

“The camera network helped us conclude that there was only one rat on island, and it was instrumental in determining where to lay toxic baits.”

“The AI cameras sent us alerts when the rat was seen on camera. This gave us real-time information about the rat’s location and direction of travel which really helped us target it,” explains Claire.

The rat was filmed stocking up on toxic bait over four days in August, and since 8 August there have been no further sightings on the network of cameras. Last week a DOC rodent detection dog and handler, undertook a sweep of the island with no detections – giving DOC confidence to declare the rat dead. 

The eradication is a big relief as the island is a key recovery site for one of New Zealand’s rarest birds, the tūturuatu/shore plover, with just 250 individuals remaining nationwide. A single rat could have devastated the small island population. 

“Boat owners can help keep islands pest free by checking their vessel and gear for rats, mice, ants and skinks before departure. You can also set traps or bait stations on your vessel and in the area it is stored.”