How to get inked in the name of conservation.
AOTEAROA NEW ZEALAND HAS THE HIGHEST RATE OF THREATENED SPECIES ON EARTH. THANKS TO INTRODUCED PREDATORS LIKE STOATS, FERRETS, WEASELS, POSSUMS, RATS, HEDGEHOGS AND HUMANS, MORE THAN 80% OF OUR BIRDS AND REPTILES, AND MORE THAN 70% OF OUR FRESHWATER FISH, ARE ENDANGERED. PESTS KILL SOMETHING LIKE 26 MILLION NATIVE BIRDS EVERY YEAR. OUR COUNTRY IS THE FRONTRUNNER IN A RACE NOBODY WANTS TO WIN, AND THE FINISH LINE IS EXTINCTION.
Fortunately, predator eradication has become a national movement. Predator Free 2050 is government policy and the Department of Conservation estimates 200,000 New Zealanders are involved in conservation in some way, including controlling introduced mammalian pests through trapping, hunting and poisons. But how do we monitor the success of these efforts? And how to assess their impact on both target and non- target species?
One answer may lie in another area New Zealanders are world-leaders in: ingenuity. In this case, the
ingenuity is in the form of tracking tunnels, armed with bait and a sticky ink pad. Visiting beasts leave behind footprints; calling cards that can be used to identify species, sex and population density.
It’s possible to learn a lot from inky prints, if you know what to look for. Stoats and weasels have furry feet, the hairs clearly visible as ‘fluffy’ marks between the more solid ink spots made by toes and pads. Possums are easy to identify because, in addition to large feet, they have a distinctive opposable ‘thumb’ on the back foot, and hedgehogs, weirdly, have four toes on their front feet and five on the back. Yes, they are cuddly. They are also bad news, preying on lizards, grasshoppers, invertebrates and the eggs of ground nesters like the banded dotterel. Introduced by homesick colonists, there are now between two and four hedgehogs for every hectare in Aotearoa.
Female mammals can be identified by their wide hips, which place their back footprints slightly outside of the front ones, creating a zigzag pattern, whereas males have back and front feet that are aligned, as if on railroad tracks.
“HEDGEHOGS, WEIRDLY, HAVE FOUR TOES ON THEIR FRONT FEET AND FIVE ON THE BACK”
And while tracking tunnels can’t be used to measure absolute population density (at a certain saturation point, the cards simply become too crowded with prints to count), they are a good way to track activity changes over time, or compare relative abundance at different sites. Large-scale predator free operations, such as the Rotokare fenced sanctuary in South Taranaki, also use tracking tunnels to screen for re-invading pests.
It’s not only pest species that the tracking cards pick up, but natives too. Lizards leave drag marks with their tails, as well as the delicate pattern of spots or stripes on the pads of their feet. Rows of dots indicate the passage of insect feet, which range in size from minuscule ants prints, through to cockroaches and the relatively large-footed wētā. Increasing numbers of insect prints are an indicator of ecological recovery after pests have been eradicated; rats and mice, in particular, love to eat bugs.
Tracking animals by their footprints is not a new idea. According to the Department of Conservation (DOC), the first description of tracking tunnels used to monitor mammalian abundance in New Zealand was back in 1977. The tunnels are available from a range of predator-control suppliers but prominent among these, and probably the one with the coolest name, is the Black Trakka.
The Black Trakka system was designed by inventor and conservationist Warren Agnew, whose path to making a name for himself as a predator control innovator began when he was a teacher at a small rural school. His class discovered a grey warbler nest. Full of excitement, they built a hide and used an empty coke bottle as a makeshift telescope
to observe the birds. When disaster struck in the form of a stoat, one of the most devastating predators of New Zealand birds, Warren contacted DOC, looking for information, a call, he says with a laugh, that was answered, “McFadden here, stoat catcher.” After reading through myriad DOC reports on the problem, Warren set about devising better methods to find and control these predators. His new and improved tracking tunnel system was the result.
It’s a simple concept. The tunnel is a rectangular tube of black plastic, open at both ends, pegged into the ground. A pre-inked card is inserted along the tunnel floor, clean and white at each end, with tacky black ink in the centre. A tasty treat, like peanut butter, Nutella or a cube of rabbit meat, is placed on the ink to lure hungry creatures in. Any animal wanting the bait has no choice but to walk across first ink, then white card, leaving a telltale trail of prints behind.
At the time that Warren got involved, DOC already had their own footprint tracking system in place, using a sponge soaked in food colouring as the ‘inkpad’. Instructions for a DIY version of these cards is still available on the DOC website for children and families wanting to get involved with conservation at home. However, for large scale monitoring, food colouring wasn’t ideal, as it evaporated in the heat or smudged in the wet, making many records useless.
Finding materials that would leave clear and lasting marks was the key to the success of the Black Trakka. Warren says his main challenges were finding a card that could stand up to New Zealand’s notoriously wet conditions and a long- lasting ink that wouldn’t dry up. He cracked it, patented it, and made national headlines when it was used to track down a rogue rat on Rangitoto Island. These days approximately half a million Black Trakka tracking cards are deployed each ear, in backyards, on offshore islands, and throughout nature reserves. They’ve also got an international following. In Germany and Switzerland, they’ve been used to track stoats. In Japan, it’s the mongoose, while the Americans are after rats. On Christmas Island, a Trakka trap identified a gecko that was thought to be extinct.
For at-home users, tunnels, Warren reckons, are “the only way for people to know what’s in their sections.” Recommended Trakka deployment spots in include garages, barns, decks, compost sites, and flower and veggie gardens. A tunnel will tell you more about any noxious critters making themselves at home on your property, as well
as letting you know if you’ve got more desirable neighbours like skinks or geckos hanging around.
With the Black Trakka humming along, Warren remains passionate about continuing to find better ways to catch and kill predators, particularly rats and stoats. One idea he has been working on is toxin based on cholecalciferol, or vitamin D3. When dissolved in oil, the toxin penetrates the skin and enters the bloodstream directly, meaning it could be administered by squirting an animal as it runs through a tunnel. Once absorbed, it calcifies the heart valves causing a myocardial infarction (heart attack), a sudden, relatively painless death.
For now, though, it’s all about species identification. Ink doesn’t lie, and every footprint tells a story. Let’s hope that, one day, it will be one with a happy ending.
ERIN IS A SCIENCE WRITER BASED IN TARANAKI AND HAS RECENTLY COMPLETED A MASTERS IN SCIENCE IN SOCIETY AT VICTORIA UNIVERSITY.