Wildlife Impacts on Agroecosystems and Culture: Achieving Integrated Pest Management of Invasive Ungulates in Hawai‘i

View the project final report

Commodities

• Animals: bovine

Practices

• Animal Production: range improvement
• Education and Training: decision support system, extension, farmer to farmer, networking, on-farm/ranch research, participatory research, workshop, youth education
• Natural Resources/Environment: wildlife
• Pest Management: competition, disease vectors, economic threshold, field monitoring/scouting, integrated pest management

Hawai'i lacks native ungulates, but introductions of hoofed mammals have resulted in population explosions of wild ungulates on each of the islands in the archipelago (Figure 1). Aside from domesticated livestock, these nonnative ungulates are feral, invasive, or both (Table 1). Although ungulates are a potentially unifying issue linking diverse stakeholders in meeting common challenges regarding food security and environmental health, the needs of ranchers, farmers, state wildlife managers, and hunters have largely been viewed as competing, rather than complementary. State agency management of game in Hawai‘i, in contrast to the continental states, does not extend to private lands, creating a tremendous management burden for producers on private lands. Meanwhile, producers on state lease lands find themselves in a position of accommodating hunting access and regulations that may directly hinder their operations or prevent them from optimizing conservation practices. By identifying individual landowners and managers as decision makers for land parcels, while simultaneously addressing issues of land adjacency and potential synergistic solutions amongst stakeholders, we are contributing to collaborative change in ungulate management to increase stability and sustainability for agriculture in Hawai‘i. In this project we determined relationships between ecological and economic health of ranch and agricultural lands, identified densities of unmanaged ungulates, and developed data-driven Integrated Pest Management (IPM) decision guidelines to improve on-farm wildlife management and profitability.

Related WSARE projects have successfully quantified economic damages from wildlife to livestock (Elser et al 2019) and highlighted benefits of native wildlife to agroecosystems (Smith and El-Swaify 2006; Price et al 2021). Negative impacts of unmanaged ungulates are well-documented in native, non-agricultural ecosystems (Leopold & Hess 2017), but prior to this project, economic damage and forage loss from wild nonnative ungulates inhabiting agricultural lands had not been quantified in the Hawaiian Islands.

In this project we surveyed for ungulate presence and impacts using economic, social, and ecological criteria. The economic component of this project demonstrated that wild unmanaged ungulates are major pests in the Hawaiian Islands, decreasing productivity and seriously threatening the viability of ranching in Hawai‘i. Further, the field component of this research demonstrated that more than 60% of sites had a decrease in forage due to invasive unmanaged ungulates, and a number of sites had a substantial amount of bare ground due to ongoing drought conditions compounded by overgrazing by wild ungulates. While not quantified in this study, we received reports of a number of small ranchers ceasing ranching activities or even selling their ranches due to these combined impacts of drought and wild ungulates, and most ranchers reported reductions in herd size.

We note that wild ungulates are still valued by both hunters and producers for recreation, cultural practices, and food security (Conover 1998, Lohr et al. 2014, Luat-Hūʻeu et al. 2021, Luat-Hūʻeu et al. 2023). Thus, in this project we also identified management actions that improve ranch production, profitability and accessibility, reduce pests, and increase native biodiversity, while respecting cultural values. To achieve these integrated values, our project leadership team includes native Hawaiians, hunters, ranchers, and conservationists. Further, our research is co-developed with native Hawaiian practitioners and experts, and we work alongside agricultural and natural resource management experts to implement, interpret, and publish our research. Thus, the experimental design, the implementation of research, and the interpretation of results are guided by native Hawaiians, ranchers, and other land managers, ensuring that results are efficiently integrated into on-the-ground actions.

Over the last three years, a combination of commercial harvest, fencing, targeted hunts by community members and land managers, and aerial shooting by land managers has substantially curbed the exponential growth that Axis deer were previously experiencing. A considerable increase in investments in deer fencing by the state legislature, counties, USDA, and other grants has reduced the movement of Axis deer (and other wild ungulates) between regions, decreasing impacts in some places but also increasing impacts to some places where removal efforts have not yet been intensified. Ranches are working with community hunters where feasible to reduce Axis deer and Mouflon sheep impacts to ranches while feeding communities. Commercial hunting, while largely limited to a single operator contracting with multiple land managers, has been hugely effective in knocking down populations while demonstrating a viable business model. Funding provided by the state to support aerial shooting knockdown efforts, where requested by ranchers, has been implemented by state agencies, who hold the only permits for such activities. Thus, despite impacts from devastating wildfires and ongoing droughts during the project period, substantial progress has been made in increased collaboration among land managers, funding for fencing infrastructure, and a deeper understanding regarding the level of effort needed to minimize impacts to ranches from invasive unmanaged ungulates.

These substantial reductions in Axis deer abundance are expected to improve forage, crop, and soil quality/quantity for producers, improve livestock production, incentivize hunting of invasive ungulates, and improve public relations, marketing, and conservation values for producers (Sergio et al. 2006, Ribaudo et al. 2010, Wilcox & Giuliano 2011, Brondum et al. 2017). Ecological benefits include better biodiversity conservation and decreased soil erosion in watersheds and coastal ecosystems. However, we note that the recovery of vegetation and soil is dependent upon how degraded the system became prior to the reduction in wild ungulate grazing, as well as factors outside of producers' control such as the ongoing drought conditions and upstream management of water and vegetation. Monitoring of these systems over the coming years, following the completion of fence building and expansion of control activities, will be critical to determine appropriate levels of wild ungulates within different fencing units. While the appropriate number in many units will be zero given the sensitivity of crops or ecosystems, a desire for commercial and community hunting opportunities may result in some non-zero number. Future studies are critical to support producers and land managers in determining what these numbers are and how to maintain them. Further, we highlight that while considerable progress has been made within the county of Maui Nui where Axis deer occur and impacts are dire, Mouflon sheep on the island of Hawai'i have not yet received equivalent efforts. It is our hope that the collaborative efforts and investments in Maui County will serve as a model for other islands experiencing similar impacts from other wild ungulate species.

Extension activities included publications, webinars, workshops, producer events, targeted youth outreach, and website development. To provide structured recommendations to producers based on our research results, we considered criteria from multiple stakeholders to determine IPM recommendations, seeking conservation of native species and culture while providing local food security through protection of crops, increased accessibility of protein from ranching and hunting, and decreased sedimentation run-off to coral reef fisheries. Results have been shared with communities in workshops with ranchers, producers, and other community members, annually at the Hawai'i Cattlemen's Convention both via tabling and in formal presentations (~500 attendees each year), at the Hawai'i Conservation Conference (~1200 attendees each year), in online public presentations, as well as via ongoing meetings with collaborative partners at ranches and government agencies. Two peer-reviewed publications regarding the direct and indirect economic impacts to ranches have been produced, one of which was published in 2024 and the other is currently under review. A two-chapter Master's thesis regarding forage impacts was also completed in May 2025 and is being prepared for publication in peer-reviewed journals. Video-based interviews with cultural practitioners regarding wild ungulates were obtained in spring 2025 and a synthesis of interviews was completed in the summer of 2025.  Table1_ungulates_WSARE

Research Objectives:

1. Quantify economic impacts of invasive, unmanaged ungulates to agriculture in the Hawaiian Islands. (completed fall 2024)
2. Quantify impacts of unmanaged ungulates on forage production in agricultural landscapes in Hawai‘i. (completed spring 2025)
3. Identify cultural significance of managed and unmanaged ungulates in agricultural landscapes of Hawai’i. (completed July 2025)
4. Identify culturally appropriate and economically viable methods of control for unmanaged ungulates, in order to improve food security in Hawai’i. (completed spring 2025)
5. Educate stakeholders and policy decision-makers about the impacts of unmanaged ungulates on economics, agriculture, food security, and ecosystems in Hawai'i. (completed fall 2024)
6. Develop decision support guidelines that facilitate stakeholder choices for economically viable and culturally appropriate Integrated Pest Management Practices (IPM) for these ungulate populations, in order to mitigate damage to agricultural lands and ecosystems in Hawai‘i. (completed July 2025)

Education Objectives (ongoing throughout project)

1. Educate stakeholders and policy decision-makers on the impacts of wild ungulates on agriculture and food security through Peer-to Peer learning modules and workshops.

2. Use Peer-to-Peer learning modules to increase awareness, and knowledge, skills, and abilities of stakeholders to recognize and discuss potential impacts of wild ungulates.

3. Educate stakeholders on culturally appropriate IPM practices developed to control wild ungulate populations and mitigate damage to agricultural lands.