The ecosystem altering impacts of feral pigs have been widely documented around the world. However, a general framework for their control and management has been lacking, especially in island ecosystems. One reason for this lack of management is that we have little knowledge of how pigs move through different island ecosystems, especially ones that are topographically challenging such as Hawai‛i. With recent advances in telemetry and movement modeling, it is now becoming practical to understand where these large introduced animals are moving and how they are using habitat. Hence, the primary goal of this study is to understand feral pig movement in terms of terrain, slope restrictions, and distance traveled beyond a natal site, within an island forested landscape. Based upon this goal, the objectives were to (1) assess different methods of time-series analysis in terms of animal movement and home range, and (2) use the information to inform wildlife management and policy. In 2008, a total of 36 feral pigs were collared with Global Positioning System (GPS) units across four different field sites on three Hawaiian Islands (Maui, Molokai, and Kauai) and tracked for an average of 60 +/- 10 days.
Results/Conclusions
Of the 36 collared animals, only four could be used for analysis due to various technological failures. Using three different movement modeling approaches (Brownian Bridge, minimum convex polygon, and the kernel density estimator), we found that feral pigs, within the heterogeneous landscape of Hawaiian watersheds have a spatial recognition limit or ecological neighborhood of between 1.65 and 2 km. All three methods indicated a slight variation of individual home range estimates. These results demonstrated that pigs move less in heterogeneous and heavily vegetated ecosystems. Even under the most conservative estimate, pigs moved 0.2 km/day. Considering that feral pigs disperse exotic plants and increase nutrient loading of streams, our results indicate that even a small abundance of pigs have a very large impact on the native ecosystems of Hawaii, due to their concentration around a natal site or resource center. Based upon this work, we suggest that managers must increase measures to limit habitat connectivity, such as perimeter fences and trapping along remote roadways that are used as feral pig dispersal mechanisms.
