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
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 people—like poisoning rabbits, dumping unwanted cats in riverbeds, or trapping rats and stoats—may 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.
References and research papers
- DOC: Animal pests A-Z
- DOC: Trapping guide
- DOC: Predator Free 2050
- DOC: Predator Free 2050 Rangers
- DOC: 2019 Mega mast
- Landcare Research: Vertebrate Pests
- Interactive field guide: Pest Detective
- Landcare Research: Wildlife & Ecology Management (research team)
- Landcare Research: Mast years and ‘mega mast’
- Predator Free New Zealand Trust (includes a wide range of resources, tips and tricks)
- 2022: Ashley Rakahuri Pest Management Plan
- 2021: Barrett The commercialisation horizon of new pest tracking and control technology (Braid Seminar)
- 2017: Schori; Introduced mammals as drivers of population decline in braided river grasshoppers (BRaid seminar)
- 2017: Norbury; Messing with the mind: using unrewarding prey stimuli to reduce predator impacts (BRaid seminar)
- 2017: Pickerell; Mammalian predator presence on braided river islands: implications for management (BRaid seminar)
- 2016: Sir John Key’s Predator Free by 2050 announcement (NZ Government)
- 2014: O’Donnell et al; Impacts of introduced mammalian predators on indigenous birds of freshwater wetlands in New Zealand New Zealand Ecological Society (Open access PDF)
- 2013: Pickerill et al; How can we detect introduced mammalian predators in non-forest habitats? a comparison of techniques New Zealand Journal of Ecology (Open access PDF)
- 2013: Norbury et al; Invasive mammals and habitat modification interact to generate unforeseen outcomes for indigenous fauna ESA doi: 10.1890/12-1959.1
- 2012: Sir Paul Callaghan’s crazy idea (The Listener)
- 2001: Dowding & Murphy; The impact of predation by introduced mammals on endemic shorebirds in New Zealand: a conservation perspective Biological Conservation (Open access PDF)
- See also Ecology/references