Stoats make a splash

September 16, 2013, University of Waikato
Stoats make a splash
Ten stoats from Lincoln University, were put into a water-filled flume with a continuous current flowing through it, to watch how far they could swim.

Stoats are generally considered capable of swimming up to about 1.5km, but the discovery of a stoat on Rangitoto Island (3 km offshore) in 2010, and another on Kapiti (5 km offshore) in 2011 suggested they may be able to get their little legs paddling for much greater distances.

Experiment on the distance a stoat can swim

University of Waikato Associate Professor Carolyn (Kim) King and a team from the Faculty of Science and Engineering decided to find out just how far.

So she bought ten stoats from Lincoln University, flew them to Hamilton, allowed them to jump into a water-filled flume with a continuous current flowing through it, and watched them go.

One female – clearly the Lauren Boyle of the stoat world – covered 1.8km in nearly two hours non-stop swimming, while three others swam strongly for more than an hour and another four chalked up between 20 and 40 minutes paddling.


Only one struggled with the swimming, having the stoat equivalent of a panic attack after about ten minutes in the water while the other was suffering from a , so was retrieved after a few minutes. After their swimming efforts, the stoats were taken for blood tests to measure their blood glucose. Those which swam longest had consistently lowered , consistent with induced by .

While the results were not conclusive, the study did show that stoats were capable of swimming much greater distances than previously thought, a fact which has implications for offshore island wildlife sanctuaries once believed to be at little or no risk of invasion by stoats.

About 250 of New Zealand's are reserves, and many of them shelter various threatened and endangered .

Issue of reinvasion on offshore reserves

More than 100 islands have been cleared of invasive mammals, but the problem of reinvasions from the mainland remains a serious issue.

Maud Island in the Marlborough Sounds is only 900m from the mainland and has been reinvaded by pregnant female stoats three times since 1982, while stoats long ago populated Chalky Island in Fiordland, which is 2.5km from the mainland but accessible via three intermediate islands.

The generally accepted risk-zones around islands 1.5km offshore "have been seriously underestimated," Associate Professor King says.

While her tests showed that at least one captive stoat could swim 1.8km in nearly two hours, "a fit and active wild stoat free to choose its own time, motivation and swimming speed might swim much further, especially given the added buoyancy of salt water".

One stoat in the tests also showed an ability to rest while floating, which could extend their range even further, Associate Professor King says. Favourable currents, floating logs or stepping stone islands would also increase their range.

Females, though smaller than males and invariably pregnant, showed no signs of being inferior swimmers, and posed a "special risk" to islands they reached through their ability to start a new population through sibling breeding – as happened on Kapiti.

The team concluded the tests, plus independent modelling, show islands less than 3.5km offshore should still be considered at risk of invasion by stoats and the common assumption that permanently maintained traplines on such islands were not necessary was "a false economy".

Associate Professor King's research is due to be published in the academic journal Biological Invasions. She will also deliver a talk about her study at the Ecological Society conference in Auckland in November.

Explore further: On genetic treasure island, voles show DNA antiquity

Related Stories

On genetic treasure island, voles show DNA antiquity

September 6, 2013

( —With its snubby, blunt nose, small, furry ears and short tail, the Orkney Islands vole may not seem significant, but it harbors genetic secrets that can help shed light on novel evolutionary and colonization ...

Rare parakeets to populate gulf islands

January 29, 2008

An ambitious plan to translocate 100 kakariki (red-crowned parakeets) from Little Barrier Island to two other Hauraki Gulf islands as well as a mainland site means more people will be able to see the rare birds.

New Zealand bird outwits alien predators

June 4, 2008

New research published in this week's PLoS ONE, led by Dr Melanie Massaro and Dr Jim Briskie at the University of Canterbury, which found that the New Zealand bellbird is capable of changing its nesting behaviour to protect ...

Recommended for you

Packing a genome, step-by-step

January 18, 2018

Genome folding now has a playbook. A new step-by-step account spells out in minute-time resolution how cells rapidly pack long tangles of chromosomes into the tiny, tightly wound bundles needed for cell division. Cells reel ...

First look at pupil size in sleeping mice yields surprises

January 18, 2018

When people are awake, their pupils regularly change in size. Those changes are meaningful, reflecting shifting attention or vigilance, for example. Now, researchers reporting in Current Biology on January 18 have found in ...

Hunter-gatherers have a special way with smells

January 18, 2018

When it comes to naming colors, most people do so with ease. But, for odors, it's much harder to find the words. One notable exception to this rule is found among the Jahai people, a group of hunter-gatherers living in the ...


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.