Success for pest elimination trial

anti-1080 sentiment sometimes focus on the methods and not on the goal, says Bramley. The goal is to clear New Zealand of these predators to preserve and then grow biodiversity, he says.

For 55 days after the last 1080 drop, rangers monitored a ‘‘core detection area’’ of 394ha with cameras, chew cards and tracking tunnels that reliably turn up evidence of live possums and rats.

This was the representative sample plot and worked something like political polls that sample small populations to extrapolate what the entire voting public thinks about politicians.

And like polls, there’s room for error. Finding no live possums or rats in the sample plot doesn’t mean they weren’t there, just that they weren’t detected. It’s also the case that possums and rats may have been alive outside the sample plot.

But representative sampling is statistically valid and Zip thinks it got to fewer than one possum per 400ha, the point where the population is ‘‘no longer functionally viable’’.

‘‘For possums it looks like it’s doable [complete elimination],’’ says Bramley. ‘‘For rats we’re not so sure and that’s largely because in Haast our starting population was very low.’’

With the experiment over, it is presumed possums and rats have started re-invading the wedge.

But Zip has plans for another trial that will attempt to permanently defend this area from re-invasion. The location is still to be confirmed. Bramley expects rivers will do most of the defending, especially for possums.

But Zip will also deploy trapping knowledge and techniques it has been refining at a research facility in Marlborough for several years. That research shows possums moving into a new area will be caught by traps placed about every 50ha.

Zip will also expand the drop zone to about 10,000ha, an area about four times larger than was targeted this year.

Zip tends not to publish its research in scientific journals but posts reports and results to its website, zip.org.nz. were required to exterminate those few rats already in the province and kill all that came in subsequent years. More than 65 years later they’re still working, mostly with toxins.

Alberta has many natural advantages when it comes to rats. Long, cold winters suppress rat numbers. Their spread in warmer months is stopped by the tall Rocky Mountains along the west border, ‘‘badlands’’ along the south border with the US, and boreal forests in the north. It is landlocked.

The vulnerability is the largely rural border with southern Saskatchewan, which is a manmade line on a map running northsouth. Every building in a rat control zone 29km deep and 600km long is inspected annually. Farmers in the zone are encouraged to maintain traps or call publicly funded exterminators if an infestation is detected.

A province-wide public education campaign motivates Albertans to be vigilant about rats and report sightings. It’s said Albertans are proud to be free of rats. Keeping them as pets is illegal.

When rats inevitably arrive by plane, train and truck, they are detected and killed, Alberta officials maintain. Most that arrive are singletons that don’t breed, they say.

Of course, there are sceptics especially on the internet who say rat-free Alberta is impossible.

But it’s also possible to see in Alberta New Zealand’s future once a pest species is eliminated from an area: plenty of public education, official vigilance and extermination teams that arrive commando-style when an infestation is detected.