How eradication almost didn’t happen
Lee Barry
October 2021 marked 25 years since rats were eradicated from Ka¯ piti Island, making it one of the first and largest predator-free island sanctuaries. To celebrate, the operational team reunited in the old whare on Ka¯ piti. Biodiversity ranger thinks back to the events leading up to the declaration of the island as officially predator free.
The deafening chatter of the birds is what hits you first. From the musical taunting of the t¯ıeke and the chattering ka¯ka¯riki, to the screeching ka¯ka¯ and cackling tu¯¯ı; these decibels of birdsong are the soundtrack to Ka¯piti Island.
And they’re all here thanks to one intense push 25 years ago to make Ka¯piti officially predator-free.
An iconic island
Ka¯piti is, in a word, iconic; the large barrier island shelters the coast from offshore weather and gives the area a beachy climate, its name, and a classy motif. Classified as a nature reserve, the island sits alongside a few other precious DoC sites as the most protected land in the country. It is highly significant to Ma¯ori, being Te Rauparaha’s stronghold, the scene of tragic battles, and a Te Tiriti signing.
But these days it is most recognised for its birds, thanks to being free from all mammals for decades.
On October 15, 1996, the second poison operation to rid Ka¯piti Island of rats was completed. So how did this happen? Well, it almost didn’t.
Pioneering new methods
The attempt to eradicate rats from Ka¯piti was significant. The possum eradication a decade earlier was a long, tough, gutsy slog by a few tenacious men and their dogs, but the rat eradication was truly brave.
The island is 1965ha of dense bush and long valleys. No one, anywhere, had ever attempted to rid an island of this size of rats before.
The closest in size were around 10 times smaller and had targeted only one species, while this attempt aimed to eradicate both kiore and Norway rats. Significant, yes. Optimistic, absolutely. Foolhardy? Nah; our team was up for the challenge.
Architect of the revolution
The architect of the mission was Raewyn Empson, a threatened species officer for DoC’s Wellington Conservancy.
At the time, DoC was seeing great success from the smaller island eradications of rodents using methods not available in the past: accurate application of toxic bait from helicopters. This, back then, was revolutionary.
Raewyn recalls the operation wasn’t supposed to be so late in the year; winter is the best time for rodent control, when rats are hungry and their numbers are lowest. By spring they start to breed again, which adds more pressure to a population control. Unfortunately, the winter of 1996 brought an unwelcome challenge.
“The bait was still held at the factory — it was due to be delivered the day of each aerial operation, so we didn’t need to worry about storage,” Raewyn said. “The guys at the factory opened the bags of bait to check it when we confirmed the good weather window. They rang me to tell me that the bait — all
30 tonnes of it — was mouldy and couldn’t be used.
“Having had everyone on standby for several weeks waiting for the right weather, ready and raring to go, it was a real blow.
“New bait had to be manufactured and cured, which would take weeks. It was too risky to spread just one lot of bait — the second was a necessary backup in case there were any gaps in distribution the first time around.”
The actual drop was the culmination of years of work — including two trial drops of non-toxic bait and on-the-ground monitoring to keep non-target species safe.
Weka were transferred off the island temporarily after they were shown to be at risk from eating the pellets, while takahe and pateke were held in enclosures to keep them safe from harm.
Time for plan B
The logistics of such a late change to the bait drop plans is mind-boggling.
Raewyn convened the advisory team to confirm that though the drop was postponed it would still go ahead. This involved renewing the necessary permissions, rebooking helicopters, boats, and dozens of personnel, re-issuing public notifications, replanning the captive management of non-target species such as weka and
much, much more.
So Ka¯piti’s rats were spared a few extra months. But ultimately, they were hit by two mostly-aerial applications of brodifacoum poison, — one in September and one in October 1996.
But the work was not done. If any rats survived, there was an agonising wait ahead for Raewyn and the team.
Rats would take two years to rebuild to detectable numbers, so a network of hundreds of tracking tunnels was laid across the island and checked in 1998. Not a single print was found.
In 1999, Conservation Minister Nick Smith declared Ka¯piti Island ratfree and free from all mammalian predators.
25 years later
In October 2021, key members of the team who made the rat eradication possible reunited on Ka¯ piti. The yarns and wine flowed while t¯ıeke serenaded the gathering. There were heated discussions about the date of additions to the old whare, the homestead where workers bunked together for months. Excerpts from the project’s daily logbook were read; this isn’t as dry as it sounds, much of it telling the story of a committed team who looked out for each other.
Those gathered shared their huge sense of pride at their achievement with words shared and a toast raised, both to those who couldn’t attend and those who are no longer with us. Every visitor to Ka¯ piti Island would thank them — if only they knew — for completing the almost impossible mission that changed the face of island conservation in Aotearoa forever.
With dozens of Predator-Free projects on the go around New Zealand, and the aim to eradicate all of these baddies by 2050, anyone who has the chance should visit Ka¯piti Island, which is now 25 years down the track and very loud about it. For those of us lucky enough to live and work on Ka¯piti, we hope everyone in New Zealand will one day be surrounded by a thriving bird population.