A single pregnant female stoat that got into Whangaparāoa’s Shakespear Open Sanctuary last spring gave birth, resulting in the biggest challenge to face the sanctuary since it opened 10 years ago.
Two juveniles have been caught, but it is thought that as many as seven stoats could remain at large within the pest free fence.
It’s the biggest single stoat incursion since the sanctuary became pest free in 2011 – in that time, five stoats and one weasel have come in as single animals and all were found and eliminated before any gave birth.
The voracious predators are described by the Department of Conservation as “public enemy number one for NZ birds”. In 2015 a single stoat wiped out an entire population of 50-60 saddlebacks (tieke) at Orokonui Ecosanctuary in Otago and open sanctuaries senior ranger Matt Maitland says this is very much in his mind as they try everything to eliminate the stoats.
All birds are vulnerable to stoats, especially species that spend time on, or near, the ground such as tieke, kiwi and stitchbirds (hihi).
The impact on Shakespear’s North Island tieke population is already being felt. Fifty were released in the sanctuary in 2018, and have settled in and bred well – volunteers expected to find around 100 in a survey in March, but found only 30, which Matt says is likely to be because of stoats.
The sanctuary is also home to a growing population of little spotted kiwi – a small species that never gets large and strong enough to fend off a stoat. Matt says this is key to why this kiwi species is absent on mainland NZ, except in sanctuaries.
Recent investigations within the sanctuary have revealed a number of sites where stoats keep birds they have killed to consume later. The sites included dead kereru, tui and bellbirds.
Since the stoat was first discovered on camera footage, finding and eliminating it, and its young, has been the key focus. Stoats are wary of the standard trap boxes that are the mainstay of predator control programmes.
A specially trained stoat dog has been brought in once a month, helping to reduce the size of the search area. Technology is also being harnessed including thermal imaging cameras. Matt hopes to introduce traps that can be monitored remotely and volunteers are continuing their surveillance. Advice has been sought from the sanctuary’s wide network of conservationists.
Matt says because this is a mainland open sanctuary it was always understood that something like this could happen.
“Yes, this is our worst fear, but it is also the reality of being open to the public and having highly vulnerable species living here,” he says. “The need to help these populations is such that it’s seen as an inevitable risk.”
He says the most likely way the stoat got in is via the coastal ends of the pest proof fence.
“The fence across the peninsula’s ‘neck’ is cheaper than ring fencing like some sanctuaries, but the fence does end, and those ends can be found. Extensive buffer control on regional parkland by Council staff and Shakespear Open Sanctuary (SOSSI) volunteers, along with wider pest control by Pest Free Hibiscus Coast, aims to reduce the number of pests that gain entry.”
Transport via vehicles, or even boats, are other possibilities. With more than 600,000 visitors per year, Shakespear is the country’s most accessible and visited wildlife sanctuary. The movement of people, vehicles and camping and picnic gear is largely unrestricted.
“We ask all visitors to be vigilant and check for stowaway pests before they visit. However, the cooler months often mean vehicles provide attractive hiding spaces for small mammals and infrequently used equipment like camping gear can benefit from a good shakedown to check for pests before entering the sanctuary.”
Matt says the sanctuary is proud of the native species that have been brought in, and is doing everything possible to keep them safe.
“We are really concerned. Only with time will we find out what it really means. We have to confront the reality that the reason these species disappeared outside the sanctuary is now amongst us. The resilience of those populations will be important, including their ability to bounce back.”
Stoats are mustelids, along with weasels and ferrets. All three were introduced to NZ as early as 1879 to control rabbits that were destroying sheep pasture. From very early on, stoats had a devastating effect on NZ’s unique birdlife.
• They are found from beaches to remote high country, at any altitude up to and beyond the tree-line, in any kind of forest, in scrub, dunes, tussock, and farm pastures. They are known to live near human settlements.
• Stoats are agile climbers, and hunt at any time, day or night. They can swim across water gaps of up to 1.5km to reach islands. They disperse freely and individual juveniles have been known to travel over 70km in two weeks.
• Dens are well hidden. They include holes in tree trunks and rabbit burrows.
• Stoats are voracious, relentless hunters, described as having only two reasons for living – to eat and reproduce.