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Collective action to eradicate rats and mustelids from a large, peopled landscape: A social-ecological approach
ZEALANDIA Ecosanctuary

Collective action to eradicate rats and mustelids from a large, peopled landscape: A social-ecological approach

Read the latest report by Zealandia Centre for People and Nature researchers, Dr Julie Whitburn and Dr Danielle Shanahan about the social-ecological approach of Predator Free Wellington. 


The control or eradication of introduced mammalian predators is one of the most urgent tasks for conserving native wildlife in Aotearoa New Zealand (Elliot et al., 2010; Innes et al., 2010). Predator Free Wellington (PFW) is a collaboration between several key organisations, community groups and the wider public which seeks to eradicate mammalian predators (rats, possums and mustelids) from Wellington City to enable native biodiversity to thrive. In 2019, PFW began a large-scale eradication of rats and mustelids from the urban landscape of Miramar Peninsula; this has driven a significant reduction in the presence of predator mammals in the area.

This report seeks to:

  1. Harness the social and ecological learnings from this pioneering eradication effort.
  2. Examine the evidence of both social and ecological outcomes resulting from the project.

This report is underpinned by four primary sources of material that inform these aims:

  • • Key informant interviews that provide an in-depth exploration of PFW’s methods for mammalian predator eradication and engaging community action, as well as information on social and ecological outcomes

  • • Documentation supplied by PFW about their methods and structure and their annual reports

  • • PFW Engagement Field Officers’ reflection and action sheets

  • • Existing data sets and reports that provide evidence of social and ecological outcomes.

This report outlines the social-ecological approach that PFW has taken for the eradication. PFW’s strategy had two interconnected arms – the technical plan and the community engagement plan. A ‘remove and protect’ model was the basis for the technical plan (Bell, Nathan & Mulgan, 2019). This model requires the complete removal of predators from an area and then protecting that area against reinvasion, including establishing a virtual barrier. PFW had a general communication plan to build their presence in the community, a targeted strategy to engage community environmental groups as collaborative partners and a tailored engagement strategy to recruit landholders’ participation within each community.

In this report we have positioned PFW’s operation within the Collective Impact Framework (Cabaj & Weaver, 2016; Kania & Kramer, 2011) which includes the process of organising and implementing both the technical aspects of a project and engaging people.
PFW Ltd. (the core team) was an independent organisation that acted as the back-bone entity of the collective and managed the many facets of the project. Such an independent entity is uncommon in community restoration collaborations in New Zealand (McFarlane, 2021; Salignac et al., 2018). Providing funding, resources, labour, technical expertise, building the capacity of the PFW team and the wider community, and promoting evidence-based learning were key functions of the core team that underpinned the impact of the project.

Evidence for ecological outcomes
The biodiversity on Miramar Peninsula has shown some signs of recovery since PFW began its eradication of predators in July 2019, but the full impact of this intervention will only be evident over the coming decades. The ecological outcomes observed include: • Mustelids (Mustela nivalis and M. erminea) and Norway rats (Rattus norvegicus) were declared eradicated in January 2021 and abundance of ship rats (R. rattus) has been dramatically reduced. The abundance of mice has not decreased in recent years.

  • • The abundance of native forest birds increased by over 50% following predator eradication. The increase was largely driven by a 49% increase in the mean number of tūī (Prosthemadera novaeseelandiae).

  • • The abundance of tūī, riroriro (Gerygone igata) and pīwakawaka (Rhipidura fuliginosa) were significantly higher in 2021 compared to 2017.

  • • There was no evidence of improvements in the abundance of tauhou (Zosterops lateralis), kōtare (Todiramphus sanctus), or kererū (Hemiphaga novaeseelandiae).

  • • Kororā, little penguins (Eudyptula minor), breeding was unchanged over the last seven breeding seasons, suggesting no benefits from the removal of rats and mustelids at this stage.

  • • Tree wētā (Hemideina crassidens) increased by over 100% at sites where rats were considered absent.

  • • The number of beetles and cockroaches decreased at sites where rats were considered absent.

  • • The recovery of native flora was not examined here. However, recovery is likely to be happening. Te Motu Kairangi-Miramar Ecological Restoration have planted thousands of natives on the Peninsula and Wellington City Council invest in planting natives across the city and support volunteer planting projects

  • • Recovery of coastal bird populations can be assessed once Greater Wellington Regional Council repeats their baseline Coastal Bird Survey from 2017-18.

Evidence for social outcomes included:

  • • In a Wellington study, people who participated in trapping were more likely to report lower levels of depression, anxiety and stress and stronger feelings of social cohesion than those who did not participate in trapping. However, this research does not prove a causal relationship, and planned repeat surveys will assist in unpacking this pattern.

  • • PFW achieved equitable deployment of traps and bait stations across the landscape, irrespective of the socio-economic context or the amount of tree canopy cover in neighbourhoods. This is an uncommon occurrence with social imbalances in environmental outcomes common globally (Hart et al., 2022). A community-by-community approach to recruitment of private businesses and householders was a key feature that promoted these equitable outcomes, and it may ultimately lead to equitable improvements in biodiversity over time.

  • • Surveys indicate an increase in support for predator eradication in Wellington City since 2017 (prior to eradication). Although 93% of Wellingtonians surveyed supported predator eradication in 2021, only 44% of people currently participated in predator control. This attitude-action gap may have consequences when PFW hands over the responsibility for biosecurity maintenance to the community. Some of the ecological outcomes reported here differ from what might be expected after undertaking predator control. Riroriro and pīwakawaka are increasing in Miramar but these species do not generally respond well to predator management (Fea, Linklater & Hartley, 2020; Miskelly, 2018). In contrast, Kererū are as yet found in low numbers on Miramar Peninsula. Kererū have been at low numbers on the Peninsula for many years and have a low reproductive rate (Casey, 2001), so may take longer to re-establish. The recovery of native bird populations is also limited by habitat quality, especially in urban areas such as Miramar Peninsula which has little native forest.

While some evidence of social outcomes has been presented here, there is much more to explore. There are many potential social and economic benefits of the eradication effort for which we have little evidence (Russell & Stanley, 2018; Wilson et al., 2018). Social outcomes are a key reason for investment in biodiversity restoration (Shanahan et al., 2018) and can motivate participation where concern for the environment is low (Russell & Stanley, 2018). Further, additional knowledge is needed to inform the transition to community-led biosecurity maintenance. In particular, how can community engagement be sustained at the level necessary to maintain biosecurity? Do the socio-ecological benefits associated with the eradication support community engagement?
The PFW project is an opportunity to partner with mana whenua, to learn from Indigenous knowledge and to uphold Indigenous rights and interests (Lyver et al., 2019; Wehi & Lord, 2017). PFW have long expressed a desire to develop a true partnership approach to running its projects, but progress along this pathway is still in the very early days. Research that explores the nature of the relationship to date, potential challenges to implementation of a partnership approach and potential pathways forward would be valuable.

PFW’s landscape-scale eradication effort on Miramar Peninsula is an exemplar of collective action which involves a long-term collaboration between community and across-sector organisations to achieve greater impact than the groups could otherwise accomplish. PFW developed a social–ecological approach, deemed necessary to address complex conservation issues, such as predator eradication, in peopled landscapes (Berkes, Colding & Folke, 2003). In addition, the project demonstrates the full range of amplification processes described by Lam et al. (2020a) as PFW worked to scale-up the existing community-led predator control activities on Miramar Peninsula.

The learnings from this research can inform the next phases of PFW’s plan in Wellington City and have particular relevance for achieving the PF2050 goals. The learnings also have long-term implications for improving large-scale community engagement in ecological restoration projects locally, nationally and internationally. The strategy’s used by PFW to interweave technical expertise and community engagement could be applied to other ‘wicked’ problems that require a systems approach, such as developing a regional response to address aspects of climate change which could culminate in community-wide behaviour change.

Read the rest of the report here: 



Tūī photo: Janice McKenna 

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