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Introduced and naturalised predators

Let’s get rid of the lot. Let’s get rid of all the damn mustelids, all the rats, all the possums, from the mainland islands of New Zealand. It’s crazy and ambitious but I think it might be worth a shot.” – Sir Paul Callaghan (2012)

Predator Free 2050

“While once the greatest threat to our native wildlife was poaching and deforestation, it is now introduced predators.  Rats, possums and stoats kill 25 million of our native birds every year, and prey on other native species such as lizards and, along with the rest of our environment, we must do more to protect them.

“This is the most ambitious conservation project attempted anywhere in the world, but we believe if we all work together as a country, we can achieve it.” – Prime Minister John Key (2016).

Apart from three bat species (one of which lives around braided rivers), New Zealand had no land-based mammals until settled by Māori and Europeans. Instead, birds and insects filled the ecological niche that, elsewhere in the world, is inhabited by mammals. Specialists in their habitats, these birds and insects had no reason to evolve defence mechanisms against comparatively more intelligent mammals.

These introduced mammals now take an alarming toll on native wildlife through predation, competition, and habitat destruction.

Braided River Predators

The goal of making New Zealand ‘predator free’ is a call to arms to remove the three most destructive species: rats, possums, and stoats.

Dig a little deeper, however, and we have learned that getting rid one species such as rats forces their natural predators, cats and mustelids (stoats, weasels, and ferrets) to turn their undivided (rather than partial) attention to our native animals. That’s an unfortunate example of the ‘law of unintended consequences’. So management strategies for dealing with predators must be based on how an entire suite or guild of pest mammals operate, not just one or two well-known predators.

And that’s not easy, because different predator guilds operate in different places, especially along rivers. The makeup of those guilds changes with the seasons, availability and type of food, climate, the actions of peoplelike poisoning rabbits, dumping unwanted cats in riverbeds, or trapping rats and stoatsmay lead to a population explosion of mice that prey on our native and often critically endangered invertebrates and lizards.

This section of the website outlines the predator species that wreak havoc our native and endemic braided river animals on braided rivers. It includes less well-known predators such as the Southern black-backed gull, now in plague numbers because of the historic actions of people, and hedgehogs, which may be endearing in Europe where they originated, but are incredibly destructive when it comes to ground-nesting braided river birds here in New Zealand.

Because predator guilds are so varied (and often unknown) if you are considering trapping or predator control  in your area, particularly when mast and mega-mast years are predicted, to avoid the ‘law of unintended consequences’ we strongly urge you to contact your local DOC Predator Free 2050 Ranger, local river care group, conservation group, or contact us for advice and assistance to ensure the best outcome. See for example the 2022 Pest Management Plan for the Ashley Rakahuri River.

DOC will also be able to show you (and help you join) an online mapping database where other traplines have been set so that you can see what’s being done elsewhere and how your project fits with others so that the goal of ‘Predator Free 2050 can be achieved.

Can innovation in detection and trapping help us meet the future challenges of climate change? : 2023 Braided Rivers presentation
Hedgehogs are some of the worst predators on braided rivers, and they can survive in surprisingly high alpine areas.
Black-backed gulls are an increasing problem
Stoat attacking a nesting black-fronted tern: the stoat killed the tern but did not eat it. (Video courtesy of Wildlife International Ltd.)

References and research papers

Setting and using the DOC200 trap