Desire can be deadly: Sex scent snares stoats in Nelson Lakes trap trial

The lure of a fertile female could be the "holy grail" for controlling one of New Zealand's most devastating predators.
Dave Hallett

The lure of a fertile female could be the "holy grail" for controlling one of New Zealand's most devastating predators.

Stoats are learning the hard way that desire can be deadly.

A pest control trial at Lake Rotoiti, south of Nelson, is using the scent of fertile female stoats as a lethal lure.

The trial forms part of a major project by the Department of Conservation, Lincoln University and Zero Invasive Predators to find a long-life lure for stoats, described as "public enemy number one" for New Zealand's native birds.

A stoat with an unlucky bird for lunch.
David Hallett

A stoat with an unlucky bird for lunch.

The method works by filling tea strainer balls with a synthetic, cotton wool-like substance that contains the scent of captive female stoats in oestrus, a period of sexual receptivity and fertility.

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The material, know as "oestrus bedding", is placed inside traditional stoat traps as bait.

Video footage shows a stoat interacting with an oestrus bedding lure. Source: DOC

Despite how it might sound, the lure of a fertile female is not all about sex.

While male stoats are voracious breeders known to sniff out and impregnate entire dens, including infants that have yet to open their eyes, the oestrus bedding has also been attractive to females.

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DOC predator ecologist Elaine Murphy, who is leading the research, said it was not yet known if stoats were attracted to the oestrus odour, or the stoat scent in general.

"I guess we're just learning about social smells and how they're attractive to stoats."

The trial in Nelson Lakes has been comparing traps with a mixture of a rabbit-based bait and oestrus bedding to traps that only have the bedding material.

After six months, there have been no conclusive findings and potential changes to the trial were being discussed at a meeting in Wellington on Thursday.

Murphy said discovering an effective long-life lure for stoat traps would be a "major breakthrough" for pest control in New Zealand, particularly given the Government's goal of being predator free by 2050.

"It's a bit like the holy grail, I guess."

Murphy said a long-life lure was needed to take full advantage of traps that reset automatically, removing the need for frequent monitoring. 

"There's no point in having a resetting device unless you have a long-life lure because you've got to change the lure every three weeks anyway.

"We're hoping that from this oestrus bedding we might be able to extract a liquid that you could use in a long-life lure."

Previous attempts to synthesise the compounds found in the oestrus bedding were unsuccessful, Murphy said.

A preliminary oestrus bedding trial in Abel Tasman National Park in 2014 found that it caught twice as many stoats compared to the traditional dehydrated rabbit bait, Erayz.

And pen trials have found that the bedding material was attractive to more than 90 per cent of male and female stoats.

Field trials in Nelson Lakes and the Coromandel were designed to see how the lure performed in the wild.

The oestrus bedding theory was developed after shredded newspaper bedding from captive female stoats was used to trap a rogue male stoat on Kapiti Island, near Wellington, in 2011.

 - Stuff

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