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Using animal behaviour to eliminate the last survivors and achieve predator freedom

“Just like a teenager,” says Manaaki Whenua researcher Dr Kyla Johnston, “he’s too lazy to do anything.” The video Kyla is reviewing shows a stoat quite content to just lie in front of a trap and not do much.

Kyla has hours and hours of video to watch as she and her research colleagues try to measure stoat ‘personality’ traits in an attempt to understand why some recalcitrant stoats are able to evade traps and other devices intended to eliminate these invasive predators.

The researchers have developed  a novel behavioural technique to quantify the responses of ‘average’ and ‘survivor’ stoats to a range of control devices and novel situations. It is the first time wild mustelid personalities have been quantified, which sees the team notching up another success in the ongoing search for a way to meet the goal to get Aotearoa New Zealand predator free.

‘Predator freedom’ is one of the country’s top priorities for protecting native biodiversity, yet complete eradication of possums, mustelids, and rats would be prohibitively expensive using current pest control methods. Current invasive predator control tools can remove most individuals in a target population but always leave some survivors. 

“Individual differences will influence whether an animal goes into a trap, how it responds to scent lures, or indeed any management action,” says Manaaki Whenua Senior Researcher Dr Patrick Garvey. “These potentially important aspects of individuality, including difference in life histories, motivations and personalities, may undermine the effectiveness of any pest control program. Therefore, it is critical to understand individual variability in pest responses as we move towards predator freedom in Aotearoa.”

“If we focus on the ‘average’ pest we fail to mitigate the damage done by ‘rogues’ (those individuals that cause disproportionate impact) and ‘recalcitrants’ (those individual animals we know avoid standard control measures),” he says. “These two groups of pests are the ones that cause most damage and are very expensive to remove.”

And it is to those survivors that Manaaki Whenua’s ‘Eradication Science’ MBIE Endeavour programme is shifting the focus of its research. For the first time, researchers are looking away from reducing pest populations and towards cost-effectively eliminating the last few surviving individuals. Understanding the behaviour of those survivors, and what motivates them, will guide the development of better-targeted control tools. 

Testing stoat personalities
Stoats were placed in an arena and we recorded their behaviours in a novel environment, such as how they respond to high risk areas (light). This allows us to quantify a range of personalities, from bold to shy. Personalities can then be linked to responses to control tools, so we can improve how we target “shy” individuals.

The ‘Eradication Science’ programme is the first worldwide to apply animal personality research to pest animal management. It seeks to reveal the behavioural characteristics contributing to some individual pests surviving control, and how we can manipulate those behaviours using novel cues and combinations of cues to overcome these survival behaviours.

Within the programme, researchers are focused on four different research aims: 

  • identifying the behavioural traits that distinguish survivors from the ‘average’ individual in uncontrolled possum, stoat, and rat populations
  • testing a range of cues that alter predators’ perceptions of risk and reward
  • investigating kaupapa Māori and kaupapa Moriori aspirations and approaches to pest control/eradication
  • using field trials to quantify improvements in control device efficacy based on the findings, but with broader areas and longer timeframes.

Four years into the programme, researchers are chalking up remarkable success. They have tested the responses of stoats to various audio lures – including prey distress calls, other stoats’ calls, and predator vocalisations. Stoats responded strongly to some of these cues including one notable success, where a stoat that evaded capture for months was lured into a trap using the sounds of baby stoats, that was collected for lure trials in the Eradication Science programme.

The potential to protect this intellectual property is being explored as it could potentially be used across a wide range of species and applications.

In a follow-up to this research, the team is testing whether a range of visual, sound, and scent cues are able to increase the interaction rates of recalcitrant animals (possums, stoats, and rats) with control devices. They will then field-test the most promising combinations of cues to measure their effectiveness in removing recalcitrant predators. This work includes evaluating the costs of novel versus standard approaches to eradication.

In an aligned project, Manaaki Whenua is investigating the effectiveness of non-lethal (sound) cues in changing predator ranging behaviour by focusing on cat movements in and around urban reserves.

Moving from exploring sound to scent, Dr Patrick Garvey is focused on developing an effective predator lure by creating a synthetic replicate of the natural predator odour of ferrets, the largest mustelid species in Aotearoa New Zealand. This was trialled in three large-scale conservation programmes, with stoat capture rates doubling at these sites when the lure was used. Iwi partners in Taranaki have recently begun a trial with the Manaaki Whenua lure to reduce the impacts of stoats on native biodiversity. 

Researchers have also discovered that female stoats are more trap-shy than males. It has been suggested differences in capture success rates between male and female stoats relate to encounter probability, as males with their larger home ranges are likely to encounter more traps. However, female stoats are much more trap-resistant, with trap recalcitrance greatest for ‘shy personality’ female stoats. Female recalcitrance could be a fundamental issue influencing stoat control efforts country-wide.

It’s not just stoats and ferrets under the spotlight. Possums, rats, and cats have all been subjected to field and pen behaviour studies.

For example, research in collaboration with the University of Canterbury has demonstrated ‘social learning’ in possums, whereby ‘observer’ possums learned to solve a puzzle device by observing a ‘demonstrator’ possum in an adjacent pen. If predators can learn about control devices in the same way, social learning could impede predator eradication campaigns.

And contrary to a popular maxim, it seems that fortune does not favour the bold. Control methods usually remove the boldest animals from the population. Groups of rats captured from sites with a history of control with toxic baits in stations were shyer and less willing to engage with various devices than rats from sites with no history of control. Bait stations are, therefore, a selective tool when used for rat population control.

The ‘Eradication Science’ programme is an ambitious endeavour, which only works because of the massive amount of collaboration between Manaaki Whenua teams, stakeholders, and management agencies. For example, the research component looking at why some possums survive standard baiting operations was complex and time-critical. All potential mechanisms needed to be investigated, including behavioural differences, microbes (such as bacteria, fungi, viruses, and their genes, which naturally live on and inside bodies), diet, demographics, feeding behaviour, and movement data. This involved a complex study design, animal capture, handling, transport, husbandry, and behavioural assays before transport back to the capture locations, all done prior to a DOC aerial baiting operation.

These programmes have solidified Manaaki Whenua’s long track-record of quality research into vertebrate pest control techniques.

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