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

Results (Organized by Project Objectives):

1. Quantify economic impacts of invasive, unmanaged ungulates to agriculture in Hawaiʻi.

Results

Shwiff et al. 2024, Pest Management Science

Survey results. The survey was administered from February 2023 to June 2023. It received 113 responses, 68 of which were complete and met validation requirements. These validation requirements included surveys that could not be used consisted of not applicable (NA) as a response to all questions, respondents who did not reside in Hawaiʻi, or respondents provided that same value for every response. Given these considerations, out of the 68 responses 45 were usable from the targeted audience of livestock producers (Fig 7, Shwiff et al. 2024).

These 45 surveys were received from five islands, representing approximately 39% of all reported pasturelands in the Hawaiian Islands (Table 1, Shwiff et al. 2024). Surveyed acres covered a significant amount of the pastureland for the islands of Hawaiʻi (43%) and Maui (46%), but lower percentages for Oʻahu (18%), Kauaʻi (6%) and Molokaʻi (6%). The survey results were compared to total pastureland data as reported by the Hawaiʻi Department of Agriculture in the latest reporting year (Hawaiʻi Department of Agriculture, https://hdoa.

hawaii.gov/salub/). There were no participants from Niʻihau or Lānaʻi in our survey. Regarding pasture estimates, we assumed for this analysis that all of the land reported in the survey was designated as pastureland.

Most of the respondents reported that wild ungulate presence in their country and on their operation had increased over the last 3 years. On Hawaiʻi, 96% of respondents indicated that wild ungulate presence had increased in their county and on their operation. For Maui, 100% indicated an increase in their country and 89% on their operation.

For most of the respondents, the livestock concern was beef cattle. The average number of livestock reported by respondents was 877 (range 0 – 15, 125, standard deviation = 2442). Beef cattle, goats, and sheep were the top three livestock species raised by respondents, and on average respondents owned two livestock species. On Hawaiʻi most producers raised cattle, with goats ranking second in terms of overall number of animals on their facility. On Kauaʻi and Molokaʻi surveyed producers primarily raised cattle. On Maui, producers reported that cattle were the primary livestock produced, with sheep ranking second which was the exact opposite of Oʻahu.

Wild pigs (present on all islands except Lānaʻi) and axis deer (present only on Maui, Molokaʻi, and Lānaʻi) were reported to cause the most damage to property and operations (Table 2, Shwiff et al. 2024). Additionally, among livestock producers on the island of Hawaiʻi (n = 28), significant damage was reported from mouflon sheep (17% of respondents), feral sheep (14% of respondents), and feral goats (21% of respondents). Producers from Maui reported a high degree of damage by axis deer (70% of respondents) and feral goats (20% of respondents).

Direct impacts. On a scale of 1 (causing minimal damage) to 5 (causing the most damage) based on the damage to their operations, most respondents rated feral pigs and axis deer as causing damage at a scale of 4 or 5 (Figure 8, Swhiff et al. 2024), while feral sheep, goats, and mouflon sheep were rated lower. Of the islands from which responses were received, axis deer are only present on Maui and Molokaʻi, and feral sheep, mouflon sheep, and hybridized feral and mouflon sheep are only present on Hawaiʻi island. The total annual cost of wild ungulates summed across all ranch operations represented in the survey was reported to be $1.42 million, with most of the costs resulting from direct damage and control costs (Table 3, Shwiff et al. 2024).

Additionally, livestock producers spent around $2.03 million in fence installation costs. The largest costs were from property damage, control, and pasture repoair (Table 3, Shwiff et al. 2024), but respondents were only asked to consider the two highest value livestock species, which were less than all livestock species raised for nearly all the producers. The summation of damage costs by island provides the opportunity to determine damage costs per acre by island. Combining the damage costs per acre with total acres allows for the extrapolation of these costs for the entire state. Two extrapolations were made. First, we utilized the damage cost per acre for the total number of surveyed acres ($4.80) and multiplied this by the total number of pastureland acres in Hawaiʻi (756,579) to determine an annual estimate of over $3.6 million in damage and control costs to Hawaiian livestock producers annually. Second, we utilized the calculated damage cost per acre for each specific island and then extrapolated that value across only that island and then summed across the islands. Extrapolating costs this way led to an overall annual cost to the state of over $7.5 million.

Producers could utilize multiple methods of control so percentage will not add to 100%. The largest cost of control, other than installation of non-electric fences, was reported from shooting wild ungulates. Excluding fencing, a variety of control methods were used, including (listed in order of respondent preference) shooting on sight, hunting with dogs, hunting without dogs, and trapping, but no respondents used repellent. Examining this same information by island reveals that producers prefer control methods suitable for the type of invasive ungulates that occur on that island (Figure 9, Shwiff et al. 2024).

To a lesser extent producer reported that trapping was effective, and the use of repellents was viewed as not effective. Respondents reported that shooting and hunting with dogs were the most effective control methods with respect to reducing wild ungulate damage (Figure 10, Shwiff et al. 2024).

Koppes et al (Under Review), Rangeland Ecology and Management

Indirect impacts. Approximately, 35% of survey respondents indicated reducing their herd size due to wild ungulate damage on rangeland. Of these producers, 76% responded that the reduction impacted their breeding herd, consistent with our previous assumptions that herd reductions diminish birthing capacity. The producers who experience a reduction in the carrying capacity of their rangeland account for approximately 16% of the total acres surveyed and over 96% of all reported damaged acreage. Among these respondents, 6% reported not knowing by how much they’ve reduced their herd, and loss values were subsequently not calculated; 41% reported reducing between 1 to 25%, 35% reported reducing between 26 to 50%, 12% reported reducing between 51 to 75%, and approximately 6% reported reducing their herd size between 76 to 100% (Figure 5, Koppes et al. Under Review).

While wild ungulate damage was reported on the islands of Hawaiʻi, Maui, Molokaʻi, and Oʻahu, reduction of livestock cattle due to forage loss was reported on only three of these islands (Hawaiʻi, Maui, and Molokaʻi). Livestock producers on Maui account for roughly 81% of the reduction in production potential while Hawaiʻi and Maui account for 17% and 2% respectively. The total cost of livestock loss due to forage loss estimated from survey reports is $2.31 million (Table 2, Koppes et al. Under Review). Summation of livestock losses by island provides the opportunity to determine income loss per acre by island. Combining the loss per acre ($7.96) with total acres (705,199) allows for extrapolation of these costs for the entire state. We limited our extrapolation to three islands (Hawaiʻi, Maui, and Molokaʻi) as these were the only islands where ranchers reported herd reductions. Using the extrapolation above, we estimated statewide economic loss of $5.6 million due to herd reduction.

Producers who had to reduce their herd due to forage loss seemed to be, on average, 15 years younger, and the respondents were more often women. Those reducing herd sizes had larger increases in wild ungulates on their ranches, higher supplemental feed costs, a higher concern regarding parasites, and had substantial amount of damage, erosion, and acreage loss (Table 3, Koppes et al. Under Review). They also differed in their management actions to address these impacts and concerns. Those who had greater reductions in herd size also hunted and culled more wild ungulates, more often used dogs to hunt pigs (Figure 6, Koppes et al. Under Review) and worked more closely with government agencies.

To rule out pasture size as a driver for these differences, we examined overall respondent reported acreage between the two groups (reduced vs. non-reduced). The average size of a non-reduced producer’s rangeland (11,061 acres; SD = 32,805) was 44% larger than that of a reduced producer’s rangeland (6,129 acres; SD = 10,804), so the differences in acreage alone did not drive the results.

When damage rates on a scale of 1 to 5 were broken down by species and reduction status, we observed that reported damage for most species (Black-tailed deer, feral goats, feral and mouflon sheep, and wild pigs) remained relatively consistent across the two groups. Where they differed dramatically was reported damage due to Axis deer (Figure 7, Koppes et al. Under Review), suggesting that the impacts are highest on islands with invasive Axis deer.

Discussion

Wild ungulates impose substantial economic costs on Hawaiʻi’s cattle industry, with damages totaling between $9.2 million to $13.1 million in combined direct and indirect costs annually (Shwiff et al. 2024 and Koppes et al. Under Review). These expenses represent a significant portion of the industry’s five-year average gross income of $53.1 million, highlighting the economic strain wild ungulates place on ranchers (State of Hawaii 2023). Despite recent gains in production and revenue, such high costs from wild ungulate damage threaten the industry’s financial stability and growth potential. Addressing these impacts is crucial for sustaining Hawaiʻi’s cattle ranching operations and mitigating further economic losses. The demographic differences between reduced and non-reduced producers also offers insights into potential management approaches. Younger producers who are more affected by these challenges are engaging actively in ungulate management but may have less established practices or resources. This trend points to a critical opportunity for targeted support and education, particularly for newer farmers who may lack knowledge or means to effectively mitigate ungulate damage.

Damage was not equally distributed among islands, a result that is not surprising given that most ranching operations are on the island of Hawaiʻi, the largest island in the Hawaiian Archipelago, and that wild ungulate assemblages differ by island. The total reported property damage costs were highest on the island of Hawaiʻi, which is consistent with the fact that most of the survey respondents were from this island and roughly 39% of the total pastureland was accounted for from the survey respondents. However, when considering the herd reductions as a result of wild ungulates, the impacts were disproportionately felt on Maui, where 81% of all producers who reported reducing herd sizes were located (Koppes et al. Under Review). A result seemingly heavily driven by the impacts of Axis deer.

Respondents on all islands reported moderate to high damage to livestock production from feral pigs, with the highest reports of damage from respondents on the island of Hawaiʻi. Producers tend to underestimate the costs associated with wild pig damage by a factor of three (Carlisle et al. 2021), indicating that combined direct and indirect costs of wild ungulates could potentially range from $25 to $40 million annually. Although the island wide extrapolated estimates from this study are significant, these annual costs likely underestimate the total cost impact to ranchers for several reasons. First, respondents were only asked to consider their two highest valued livestock enterprises, which were less than all livestock species raised for nearly all the producers. Second, the economic burden of wild ungulate damage to pasture and property on livestock operations is not limited to lost production or increased production costs; it also includes the substantial additional cost of control efforts and risk of disease transmission and less tangible ecological costs such as the value of lost soil, reduced soil health, and reduced hydrological function.

Many producers reported applying a suite of control methods, the most common being shooting wild ungulates on sight and hunting with and without dogs. Shooting on sight was also perceived as the most effective in comparison to the other methods, similar to previous studies (McKee et al. 2020). Trapping and the use of repellants were reported as less commonly used and were also perceived as less effective. Producers continue to employ methods such as trapping even though these methods are perceived as less effective, in part because these methods can be used concurrently with other methods such as shooting on sight and hunting because wild ungulates adapt to the use of any particular method over time, emphasizing the importance of not only using a suite of methods but developing new methods over time. More research on effective control methods or combinations of control methods could potentially benefit producers in their fight against wild ungulate damage. Furthermore, given that hunting pressure and the presence of hunting dogs may cause ungulate to change their distribution and behavior (Risch et al. 2022), and the need for increased fencing, collaboration among land managers is likely critical to succesful implementation of these methods.

Our research to quantify wild ungulate damage to the Hawaiian Islands suggests that improved ungulate control may play a crucial role in food safety and safeguarding livestock, as well as promoting a One Health approach to management that considers interconnections between humans, wildlife, and the environment. Targeted, well-informed, collaborative, and consistent management of invasive wild ungulates necessitates an understanding of their economic impact on livestock producers. By understanding this damage, it is posible to provide management solutions that are not only economically viable for the producer, but are considerate of the fragile island ecosystem.

2. Quantify impacts of unmanaged ungulates on forage production in agricultural landscape in Hawaiʻi.

Results

Surveys were conducted from June 2023 to March 2024. In 2023, a total of 17 sites were surveyed: 5 on Hawai'i Island and 12 on Maui. In 2024, 18 sites were surveyed: 10 on Hawai‘i Island and 8 on Maui. Three sites at Ranch D were retrieved after the 13-day period due to the catastrophic fires that began on Maui on August 8, 2023; these sites were not affected by the fires. Additionally, two study sites were established in fire-affected areas at Ranch C following a wildfire event.

On the island of Hawaiʻi where there are populations of wild pigs, mouflon sheep, feral sheep, and feral goats we detected all species except the feral sheep. Wild pigs were detected at 73% of the sites (n = 11), with 368 photos captured, 50 episodes recorded, and a maximum group size of 3 individuals. mouflon sheep were also detected at 73% of the sites (n = 11), with 11,190 photos, 1,516 episodes, and a maximum group size of 52 individuals, the highest recorded species detected on the island of Hawaiʻi. Feral goats were expected to be seen at 27% of sites (n = 4) sites based on distribution models but were only detected at 13% of sites (n = 2), with a total of 92 photos taken, 5 episodes, and a maximum group size of 15 individuals.

On Maui, all expected wild ungulates were detected including wild pigs, feral goats, and axis deer. Wild pigs were detected at 75% of the sites (n = 15), with 3,336 photos, 176 episodes, and a maximum group size of seven individuals. Feral goats were found at 5% (n = 1) of the sites consistent with expectations based on species distribution models, and producing 1,622 photos, 179 episodes, with a maximum group size of 6. Axis deer were detected at 95% of the sites (n = 19), generating a substantial 92,152 photos. There were 4,637 episodes recorded and the maximum group size for axis deer was 127 individuals, the highest recorded across all sites.

A linear mixed-effects model was fitted to assess the effects of elevation (m) and rainfall (mm) on forage production (kg/ha) for samples collected from inside exclusion cages (i.e., without exposure to wild ungulates), with site included as a random intercept. Model selection revealed that the top model included only elevation (m) as a fixed effect, with site as a random effect (Table 2; AICc = 1885.79 weight = 0.53), while models incorporating rainfall received less support (ΔAICc ≥ 1.91). The following linear mixed-effects model evaluated the effects of elevation (m), rainfall (mm), and wild ungulate abundance (RAI_grazing) on forage production (kg/ha) across all samples, including those from both inside and outside exclusion cages. Elevation was identified as the strongest predictor of forage production through model selection (Table 3; AICc = 3688.11, weight = 0.36). The second-best model, which included both elevation and RAI_grazing, received similar support (Table 3; ΔAICc = 0.51, weight = 0.28).

Linear regressions were utilized to assess relationships between average vegetation biomass (kg/ha) and wild ungulate RAI. Feral goats and feral sheep were not assessed individually as they occurred at none or at a small number of sites (Table 2.1). The relationship between wild ungulates RAI and the forage loss showed a slight positive trend (Figure 2.5; Intercept = 212.43, SE = 183.92; Slope = 17.79, SE = 15.49, t = 1.15, R² = 0.04). On the island of Hawaiʻi there was a negative trend between the total wild ungulates detected and forage loss (Figure 2.6; Intercept = 234.57, SE = 248.08; Slope = -50.44, SE = 30.47, t = -1.66, R² = 0.17) and Maui had a positive relationship between the total ungulates detected and forage loss (Figure 2.6; Intercept = 446.18, SE = 235.34; Slope = 25.41, SE = 16.77, t = 1.52, R² = 0.17). For mouflon sheep on the island of Hawaiʻi, there was a negative relationship between RAI and forage loss (Figure 2.6; Intercept = 352.35, SE = 376.84; Slope = -61.86, SE = 39.94, t = -1.55, R² = 0.11). There was a positive relationship between the RAI of axis deer and forage loss (Figure 2.6; Intercept = 451.57, SE = 231.78; Slope = 25.72, SE = 16.64, t = 1.55, R² = 0.11).

Plant species were organized by functional group (grass, forb, shrub, and lichen) see Table A1 Appendix A. The automated model selection using the glmulti function evaluated 32 models of all possible combinations of wild grazing ungulates relative abundance (RAI_grazing) with predictor variables: grass, forb, shrub, bare ground cover, and rainfall. The model with the lowest AIC value was the null model (RAI_grazing  ~ 1) with an AIC of 261.62 and 0.091 weight (Table 4), indicating that none of the predictor variables had a significant effect on the relative abundance of wild grazing ungulates across study sites (weights = 0.0005 - 0.091).

Discussion

            This is the first field study to examine the relationship between forage loss and wild invasive ungulates on ranchlands in the Hawaiian Islands. We found substantial vegetation loss at 66% of the study sites, consistent with substantial losses reported by ranches surveyed in this WSARE project. Further, wild ungulates were detected at sites where ongoing impacts from drought and wildfires resulted in a lack of forage availability for livestock, suggesting that wild ungulates may continue to degrade pastures long after they are unsuitable for ranch production.

Elevation emerged as the primary driver of forage production in both models, highlighting its strong influence on vegetation growth across sites (Table 2 & 3). The top model for forage production inside exclusion cages included only elevation as a fixed effect, suggesting that, in the absence of wild ungulates, elevation has a strong impact on forage availability (Carlyle et al., 2014; Wu et al., 2024; Zhang et al., 2023). This is likely due to environmental differences at varying elevations such as temperature (K. Yang et al., 2022; Y. Yang et al., 2023), soil fertility (Khosravi Aqdam et al., 2023), and vegetation structure (Bora et al., 2021; Han et al., 2022). The strong influence of elevation on forage production in this study aligns with findings from research on native plant cover and fire dynamics in Hawaiian ecosystems (D’Antonio et al., 2000). This study similarly identified elevation as the primary environmental driver of vegetation responses, whereas rainfall did not systematically explain variation in plant cover. When assessing forage production across all samples inside and outside exclusion cages, elevation remained the strongest predictor.

Wild ungulate abundance appeared in the second-best model suggesting that grazing pressure may also influence forage availability, although to a lesser extent than elevation. This result aligns with previous studies demonstrating that ungulate grazing reduces forage biomass alongside other environmental factors (Frank et al., 2016; Ibañez-Alvarez et al., 2022; K. Kramer et al., 2006). The relatively close model weights between the top two models indicate some uncertainty regarding the relative influence of grazing compared to elevation, suggesting further investigation into potential interactions between these factors. Rainfall, while often considered a key factor in plant productivity (Gibson-Forty et al., 2016; Heisler-White et al., 2009), did not significantly improve model performance (Table 2 & 3), but we note that there has been a multi-year drought which may have influenced study results at some sites due to severe soil alteration.

The sites where grazing ungulates were detected (n = 32), 66% had documented forage loss across the island of Hawaiʻi and Maui (Appendix Table 2). Losses per site ranged from 74.72 kg/ha to 1942.81 kg/ha in areas with preferred cattle forage. To put this into context, in two weeks ungulates consumed the food needed for 6 to 161 animal units (AU) (450 kg cow) for one day assuming one AU consumes 12 kg of dry matter per day (Heitschmidt & Stuth, 1991; Holechek, 1989; Scarnecchia, 1990; USDA, 2003). These results align with reports of ranchers reducing stocking rates or no longer rotating cattle through certain pastures due to impacts from wild invasive ungulates.

Multiple factors such as rainfall, drought, and soil health, interact with ungulate abundance to affect forage availability for ranching. Additionally, some sites were in states of regrowth following fire damage (Ranch C, sites 3 and 4), were dominated by non-preferred vegetation (Ranch D sites 4 and 7), or lacked vegetation (Ranch C, site 4; Ranch D, site 10), likely influencing visitation rates by wild invasive ungulates. Despite these conditions, wild ungulates were present, suggesting their ability to persist in areas unsuitable for cattle further exacerbating the continued alteration of pastureland.

Wild grazing ungulates (feral goats, axis deer and mouflon sheep), did not show a preference for specific vegetation types—such as grass, forbs, shrubs, or bare ground—and rainfall was not a significant predictor of their relative abundance. These findings suggest that these introduced wild grazing ungulates are opportunistic generalists, highly adaptive to varying environments (Barroso et al., 2000; Freschi et al., 2021; Newman et al., 1995; Rogosic et al., 2007; White et al., 2023). Wild ungulates may also be limited in their ability to move to areas with preferred vegetation due to barriers such as fencing or urban development. 24 out of the 35 sites had fireweed (Senecio madagascariensis) present which is a known problematic pasture weed (Haselwood et al. 1983, Le Roux 2010). The weeds compete with preferred grasses such as Kikuyu grass (Pennisetum clandestinum), which is an important pasture grass due to its adaptability (Fukumoto & Lee 2003). Due to wild ungulates adding unwanted grazing pressure on ranchlands, grasses become suppressed, allowing noxious weeds and toxic forbs to grow in place (Leopold & Hess 2016, Perkins et al. 2018).

While not significant, detections of axis deer and mouflon sheep had the highest correlation with forage loss on the islands where they occur. Previous studies have indicated that grazers reduce forage production and cause significant vegetation damage when overabundant or introduced (Marchiori et al., 2012). As our study found areas with forage loss but did not detect strong trends or significant relationships with the abundance of wild ungulates, this may suggest that vegetation damage is extensive and immediate control efforts should be implemented.

Study limitations included relatively small sample sizes for feral goats and feral sheep (Table 2.1). Additionally, the short data collection period (two weeks), limited by rotational grazing schedules, likely captured only a snapshot of the complex interactions between wild ungulates and vegetation, potentially missing seasonal variations in forage dynamics or wild ungulate behavior. Ranchers have observed ungulates moving away from certain areas after heavy rainfall (pers. Comm. Lani Petrie.). Future studies should address these limitations by increasing the number of study sites, extending data collection across multiple seasons, and integrating data such as GPS tracking of ungulate movement, vegetation recovery rates, and soil health metrics to provide a more comprehensive understanding of these interactions.

This study advances understanding of the complex relationships between invasive wild ungulates and forage loss, and points toward interactions among ecological factors beyond wild ungulate abundance alone. Further, these results highlight the need for targeted removal of wild ungulates to reduce impacts to local ranch production. Long-term research is crucial to capture the cumulative impacts of ungulates on forage loss and the environmental factors driving their movement, such as vegetation structure or rainfall patterns. Future studies should also explore ungulate impacts across diverse habitats, including native forests and agricultural crops, to develop effective management strategies for mitigating their widespread effects.

3. Identify cultural significance of managed and unmanaged ungulates in agricultural landscape of Hawaiʻi.

Results

Semi-structured interviews were conducted by our project collaborator, Carolyn Wong and digitally documented by Daniel Emhof. Interviews consisted of 18 individuals whose roles span a range of land-based practices and experiences, including ranching, farming, hunting, commercial wild ungulate harvesting, and cultural stewardship. Many participants identified with more than one role, reflecting the interconnected nature of these practices in Hawaiʻi. A total of 18 individuals were interviewed for a combined 244 minutes (4 hours) of interview time. All interview footage was collated by February, 2025 and we were in the early stages of reviewing these interviews for cultural and historical context but due to the stop work order issued by the Trump Administration work is just now resuming. For those reasons, results and conclusions will be included in the final report. We anticipate these interview videos will provide valuable insights in addition to the work already described above.

4. Identify culturally appropriate and economically viable methods of control for unmanaged ungulates, in order to improve food security in Hawaiʻi.

Results

Survey responses revealed that producers across the state rely on a suite of control methods to manage wild ungulate impacts. The most commonly reported approaches included shooting on sight, hunting with or without dogs, and fencing. Shooting on sight was the most widely utilized and was also ranked by producers as the most effective strategy. Hunting with dogs was also commonly employed and considered effective for targeting specific species like wild pigs. In contrast, methods such as trapping or the use of repellents were less frequently used and generally perceived as less effective.

In terms of economic feasibility, fencing represented the highest cost control method, with producers reporting over $2 million spent in recent years on non-electric fencing installations. These investments, while often necessary to protect pasture and infrastructure, present a significant financial burden—especially for newer or smaller operations. Producers commonly noted that no single method was sufficient on its own, and that wild ungulates often adapt to repeated use of one technique. As such, many ranchers reported rotating among several control strategies over time.

To complement these quantitative findings, semi-structured interviews were conducted with 18 individuals representing ranchers, farmers, hunters, cultural practitioners, and commercial harvesters. These interviews, totaling over four hours of recorded dialogue, are currently being reviewed and analyzed. Once completed, they are expected to provide critical insight into the cultural dimensions of ungulate control in Hawaiʻi—highlighting which strategies align with traditional values and community stewardship goals, and where management practices may benefit from cultural grounding. These perspectives will be vital to understanding how control efforts can be made more inclusive, effective, and sustainable in the long term.

5. Educate stakeholders and policy decision-makers about the impacts of unmanaged ungulates on economics, agriculture, food security, and ecosystems in Hawaiʻi. This objective is detailed under the Education Plan. 

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 the Hawaiian Islands.

This project represents the first integrated effort in Hawaiʻi to combine ecological monitoring, economic analysis, and producer-informed perspectives to develop place-based decision support for managing invasive wild ungulates. Our research documented widespread and substantial impacts of unmanaged ungulates on ranching operations across the state, with economic survey data revealing up to $13.1 million in combined direct and indirect losses annually. Concurrently, field-based monitoring demonstrated that 66% of surveyed sites showed measurable forage loss directly attributable to wild ungulate grazing, with some sites exhibiting vegetation losses equivalent to forage needed by up to 161 cattle in just two weeks. These combined findings confirm that wild ungulates are a major production-limiting factor on Hawaiʻi’s rangelands, requiring coordinated, multi-pronged management approaches to mitigate damage and support ranching viability.

While producers employ a variety of control methods, fencing, community hunting, and aerial shooting emerged as key strategies with the greatest perceived effectiveness—particularly for managing axis deer. Commercial harvesting, though currently limited to a few operators, has also shown considerable success in reducing populations and holds promise as a viable business model. However, conversations with ranchers, land managers, and preliminary analysis of interview data revealed important reservations about the long-term viability and social acceptability of these approaches.

Fencing, while widely used and often necessary in high-priority areas, raises concerns among stakeholders regarding land access, maintenance costs, and the potential for increasing ungulate pressure in adjacent unfenced areas. Many acknowledge that fencing is essential in some locations—such as around sensitive habitats or highly productive pastures—but caution that it is not a feasible or equitable solution for landscape-scale or island-wide management. Similarly, aerial shooting has proven to be an efficient population control tool when requested by landowners and implemented by state agencies, but skepticism remains—particularly within the broader community—regarding its perceived wastefulness and lack of transparency in carcass recovery or use. These concerns highlight the importance of balancing technical effectiveness with public trust, transparency, and community buy-in.

Commercial harvest has been met with cautious optimism; while it demonstrates a functional model for both population control and food security, there is concern that as ungulate populations decline in some areas, the economic sustainability of the harvest model may falter. Taken together, these perspectives reinforce the need for a diversified, adaptive IPM framework—one that considers the trade-offs, limitations, and cultural sensitivities associated with each control method.

Additionally, the distribution of impacts and access to resources remains uneven across islands, with Maui Nui experiencing greater investment and coordination compared to areas like Hawaiʻi Island, where Mouflon sheep continue to exert heavy pressure on pasturelands. These disparities underscore the need for adaptable, region-specific guidelines that consider local species assemblages, land tenure, and existing community networks. Importantly, many control strategies are shaped not only by economics or logistics but by cultural values, access rights, and trust in management institutions.

To better capture these dynamics, we conducted semi-structured interviews with 18 individuals spanning ranching, farming, hunting, wild harvesting, and cultural stewardship. These interviews are currently being transcribed and analyzed, and preliminary insights are already informing our understanding of stakeholder needs and values. Once complete, this qualitative data will be integrated with our ecological and economic findings to guide the development of culturally grounded, economically viable recommendations that reflect the complexity of Hawaiʻi’s working landscapes.

These findings have already supported the development of peer-reviewed publications, outreach materials, graduate student theses, producer workshops, presentations at major venues such as the Hawaiʻi Cattlemen’s Convention, Hawaiʻi Conservation Conference, Hawaiʻi Invasive Pest Conference. Continued stakeholder engagement, adaptive management, and long-term monitoring will be essential to provide continued support to the agricultural producers in Hawaiʻi.