New Zealand to exterminate every rat

On a bright Sunday morning the wildlife-lovers gather in Miramar, a scenic peninsula. They are on an exterminating mission.

Predator-Free Miramar aims to protect birds in this area of Wellington, New Zealand's capital, by ridding it of rats - every last one of them.

After donning hi-vis jackets, the volunteers are handed peanut butter - ideal bait for rodents - and poison.

Each is assigned a patch where they will check coil traps and toxin-laced bait boxes. "Good luck fellows," says Dan Coup, who leads the group.

A GPS app guides Coup through the bush to devices on his route. For each one he replaces the bait and updates the information on the app. None shows signs of a visit by a rat.

But as he surveys the ground for droppings and other clues, his phone vibrates. One participant has posted an image to their WhatsApp group: a dead rat in a trap.

This is not welcome news. "Dave will feel good that he's caught it, but we feel sad that there's still a rat," Coup sighs.

Eradicating rats and other predators is the goal not just for Miramar but for all New Zealand. The government expects the task to be completed by 2050.

It is a tall order. The largest territory to have removed all rats in South Georgia, a 170km (105-mile)-long island in the South Atlantic. New Zealand conservationists believe the feat can in due course be achieved in an area larger than the UK.

Others point to practical and ethical problems.

At the heart of the project is a unique ecology. New Zealand split from an ancient supercontinent 85m years ago, long before the ascent of mammals. Without land predators, birds could nest on the ground or do without flying.

Furthermore, New Zealand was the last major landmass settled by humans. In the 13th Century Polynesians brought mice and Pacific rats. Six centuries later, Europeans introduced larger mammals that feasted on defenceless birds. Almost a third of native species have been wiped out since human settlement.

Efforts to save the others are not new. In the 1960s, conservationists managed to clear rats from small offshore islands. But tackling predators did not become a social phenomenon until about 2010.

"It bubbled up and became a national totem," says James Russell, an Auckland University biologist and champion of the 2050 project.

One factor, Russell says, was the advent of infrared cameras. In the 20th Century the most visible pests, and the targets of major culls, were large herbivores such as deer and goats. But from the 2000s, wildlife enthusiasts were able to show what small mammals were up to at night.

Images of rats pouncing on eggs and chicks were widely shared. "That footage was galvanising," Russell says. An ecologist at the time reckoned that New Zealand was losing 26 million birds a year to predators.

In 2011 a celebrity physicist, Sir Paul Callaghan, popularised the dream of a predator-free country. Russell and other young conservationists argued that it could be done, given sufficient investment and mobilisation.

Politicians then got on board. In 2016 a law marked the worst predators for eradication: the three types of rats (Pacific rat, ship rat, Norway rat), mustelids (stoats, weasels, ferrets) and possums. Mid-century was chosen as an inspirational deadline.

Predator Free 2050 Ltd, a public body, was set up to channel government and private money into local projects to test eradication strategies.

The most ambitious of them is Predator Free Wellington. In a city of 200,000 people, it aims to kill off a range of pests, notably rats which thrive in urban environments.

The project's 36-strong team has turned amateur rat-catchers into proper exterminators. It has supplied them with anticoagulant poison, which is much more effective than traps, as well as the GPS app which stores information from every device in real time.

Cameras have been installed in hotspots. "If any rat shows up," says Predator Free Wellington director James Willcox, "my planning team know where they want to put their resources."

Every rat found dead is sent to the lab for an autopsy. This is crucial because anticoagulants, by design, kill slowly. Rats are intelligent social animals and learn to avoid things that obviously harm them.

As a poisoned rat dies away from the bait box, Predator Free Wellington needs the autopsies to monitor effectiveness.

"We cut them up to see if they've been killed by toxins," Willcox explains. "We also need to understand: is it male, is it female, has it reproduced recently? Are we chasing one rat or a family of rats?"

Miramar has been at the forefront of the city's offensive against predators. Rats are now a rarity on the peninsula and many native birds have made a comeback. The distinctive call of the tui, whose numbers in Wellington had dwindled to just a few pairs in 1990, is ubiquitous.

"In our back garden we now have tui flying over the whole time," says long-time Miramar resident Paul Hay. "The birdlife has absolutely taken off, especially in the last five years."

The city-wide effort benefits from an earlier conservation concept pioneered in Wellington: predator-proof fencing.

The world's first urban eco-sanctuary opened in 1999 a mile from the city centre as the tui flies. Now called Zealandia, it is protected by an 8km fence. Visitors have their bags checked and must pass through a two-door barrier that resembles an airlock.

Behind such rigorous biosecurity measures, birds that were once rare have not just survived but are spreading out to surrounding neighbourhoods.

There are now dozens of fenced sanctuaries around New Zealand. The largest, Brook, covers almost 700 hectares, three times the size of Zealandia, in Nelson in the South Island.

A year after a predator-exclusion fence was erected in 2016, the area was cleared of pests. The challenge now is make sure none get in.

Constant vigilance is of the essence. A rat might be accidentally dropped in by a bird of prey; a tree could fall on the fence, allowing a weasel to creep in.

Any damage to the fence will set off its warning system. "If the alarm goes off in the middle of the night one of us will get up there and have a look," says Nick Robson, Brook's operations manager.

Cameras and ink pads alert staff to any incursion. But the ultimate detection tool, and the predator's worst enemy, is man's best friend. "Dogs are specially trained to detect certain pests and ignore others," says Robson. "It can be that a dog can detect a rat whereas our devices haven't."–BBC