He says they present a bigger and easier target than rats or stoats, both prolific breeders. Besides being proven predators of native birds by raiding nests, possums spread bovine Tb, which can impose heavy costs on the beef, dairy and deer industries.
"We know an awful lot about possums. They're a threat to birds, our native forests, to agriculture and horticulture. They're serious broad-spectrum pests."
By blitzing Northland, Dr Clout believes a large, possum-free region would show New Zealanders that turning back the tide of predators is possible. He senses it could encourage communities to support the eradication of invasive species and assist in the survival of threatened birdlife.
"The alternative is we'll continue to lose species and we'll be the poorer for it."
Rats and stoats especially have wiped out scores of native bird species, which evolved in the absence of predators. The proportion remaining classed as threatened is one of the highest in the world.
Last week Dr Clout became a joint winner of the Marsden Medal, an award conferred by the NZ Association of Scientists and which recognises outstanding achievements in science. This week he was made an honorary life member of the NZ Ecological Society. Over the course of his career, the 64-year-old ecologist has promoted conservation and advocated for the survival of threatened species. He is an expert on the kakapo, the world's largest parrot found only in New Zealand and whose survival hinges on keeping its southern island refuges free of predators. Just 126 birds remain.
His possum vision for the north deploys Auckland, with its strategic location straddling the isthmus, as a kind of predator-proof fence against re-invasion.
"Once you've got rid of them from the northern part of New Zealand it's going to be very hard for them to get back. They're not going to swim and they'd struggle to cross the motorways.
"So it's an opportunity and chance to motivate the community and show what can be achieved."
Dr Clout accepts that the removal of possum would run into resistance from trappers who trade in fur. Landcare Research estimates the value of plucked fur in the clothing industry is up to $70 million a year.
So is it possible to have pest control and fur production? Dr Clout thinks not. "You'd have to bring the trappers on board ... The goal might take decades but we'd have to decide what we want to achieve."
He also expects poison 1080 to be around for a while. "The point is it works. It's the best tool we have for pest control on a big scale."
Dr Clout likes the idea of 2040 being the year for New Zealand to become predator-free, not just of possums but rats, stoats, weasels, hedgehogs and feral cats.
"Two hundred years after the signing of the Treaty ... it would be a great way to mark the occasion."
Spitfire set to scramble
Researchers are refining high-tech devices to destroy predators which threaten New Zealand's native birdlife.
The weapons include a "toxin delivery device" called the Spitfire which can be adapted to deal to rats, stoats and possums, an electronic pad which detects with almost total accuracy the species of pest stepping on it - which can in turn ensure the correct poison is directed at the animal - and new pesticides which enter the bloodstream and end the life of pests humanely.
The researchers say the new tools will not replace the poison 1080 - which arouses controversy because it causes deaths of non-target species, upsets deerstalkers and this year anglers who were warned not to eat trout from back country areas hit by aerial 1080 dumps.
Spitfire models designed for possums, stoats and rats have been trialled in the field. The devices have a lure to attract pests, a nozzle to spray poison gel on to the animal's fur and a pedestal which weighs the visiting predator. By setting the instrument to work for a specific weight, the device does not squirt toxin on to non-target species such as larger forest birds. Target animals sprayed with gel leave the site to groom their fur, thereby ingesting the poison.
In Abel Tasman National Park near Nelson, Project Janszoon, a trust working to restore the park's ecology, is monitoring Spitfire traps. The trust has put radio collars on 30 possums to learn how the animals respond to the traps over time.
Trust director Devon McLean said the trial was at an early stage "but it's an interesting piece of technology".
Ecologist Lee Shapiro, a PhD student and research head at Connovation, an Auckland pest control company which worked on the Spitfire development with Lincoln University and the Department of Conservation, said sealed units and the targeted spray meant only the specific predator species was killed.
Zinc phosphide, used as the toxin, awaited registration so it could be put to commercial use, which could take two years.
Dr Elaine Murphy, a senior Department of Conservation scientist, used Spitfire traps for stoat control in Central Otago. Early model traps did not cope well in the harsh winter, but modified devices showed promise.
