HAWAIʻI
UNGULATES
Publications
Insights Into Ungulate Distributions Show Range Expansion, Competition, and Potential Impacts on a Sub-Tropical Island
Derek R. Risch, Jason Omick, Shaya Honarvar, Hailey Smith, Brendan Stogner, Mackenzie Fugett and Melissa R. Price (2025)
Summary
This study examined the distribution of three introduced ungulate species, wild pigs, black-tailed deer, and feral goats on the island of Kaua‘i, where these animals both harm native ecosystems and serve as hunting resources, creating management challenges. Using motion-activated cameras and species distribution models, researchers tracked the presence of these species across the island from July 2020 to July 2021. Wild pigs were most widespread, followed by deer and then goats. The models revealed potential competition between pigs and deer and significant overlap between deer habitat and critical areas for native species conservation. Habitat preferences varied, with pigs favoring mid-elevation, moderate rainfall areas, and goats favoring arid regions. The findings underscore the differing ecological impacts of these species and offer guidance for targeted management strategies that balance conservation and hunting interests.
Figure 3. The annual distribution of wild pigs on Kaua‘i as predicted by the best-fit annual “Ensemble” model.
Figure 4. The annual distribution of black-tailed deer on Kaua‘i as predicted by the best-fit annual “Ensemble” model.
Figure 5. The annual distribution of feral goats on Kaua‘i as predicted by the best-fit annual “Annual” model.
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Environmental drivers of seasonal shifts in abundance of wild pigs (Sus scrofa) in a tropical island environment
Derek R. Risch, Shaya Honarvar and Melissa R. Price (2022)
Summary
This study investigates the distribution and abundance of non-native wild pigs, which are major ecological and economic threats and a source of human–wildlife conflict. Despite increasing research, key life history data remain limited, especially in tropical regions where pigs can shift ranges in response to climate and resources, complicating management. The study aimed to model pig distribution and abundance across two seasons, identify key environmental drivers of these changes, and explore seasonal differences with management implications. Using zero-inflated models based on field surveys and remote sensing data, the research provides insights into how pig populations vary seasonally and how this information can inform more effective control strategies.
Figure 2. Best-fit distribution models for each dataset (spring, fall, and combined).
Figure 3. Differences in relative abundance of wild pigs on Maui between the spring and fall model (a), spring and combined model (b), and fall and combined model (c).
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The global impact of wild pigs (Sus scrofa) on terrestrial biodiversity
Derek R. Risch, Jeremy Ringma and Melissa R. Price (2021)
Summary
This study used the IUCN Red List to assess the global biodiversity threat posed by wild pigs, a species with widespread ecological impacts. Despite their broad distribution and known ecosystem damage, the full extent of their threat to global biodiversity had not been well quantified. The analysis revealed that wild pigs threaten 672 species across 54 countries, including many critically endangered or endangered species, and have directly contributed to the extinction of 14 species. The study highlights that island endemics and species in non-native pig ranges are especially at risk, underscoring the widespread and serious threat wild pigs pose to global biodiversity.
Figure 1. Number of taxa described as threatened by wild pigs on the IUCN Red List of Threatened Species for each of the 17 regions. Percentage of taxa threatened by wild pigs in relation to all taxa present in each region is included in parentheses. The non-native ranges provided by Lewis et al. 2017 (dotted hatched areas) and native ranges provided by the IUCN Red List (solid hatched areas) are shown.
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A comparison of abundance and distribution model outputsusing camera traps and sign surveys for feral pigs
Derek R. Risch, Jeremy Ringma, Shaya Honarvar, and Melissa R. Price (2020)
Summary
Species distribution models are vital tools for wildlife management, but their accuracy depends on the quality and type of input data, which can vary due to methodological biases. This study compared two common monitoring methods, camera traps and visual surveys of pig sign, to model the relative abundance of feral pigs in Hawaiʻi. Although direct site-level observations from the two methods were only moderately correlated, the predictions generated from both data types using zero-inflated models showed strong agreement. Findings suggest thee two common methods of obtaining abundance data may be used interchangeably to produce comparable distribution maps for decision-making purposes. However, for monitoring purposes, sign and camera trap data may not be used interchangeably at the site level.
Figure 1. Relative abundance of pigs (Sus scrofa) on O‘ahu as predicted by (a) the average number of camera detections per site and (b) average counts of sign per site. Areas of highest relative abundance are indicated in red based on 42 spatially independent sites accessed between June and November of 2016 and 2017. Black circles indicate the locations of survey sites.
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