Movement patterns and habitat utilization of nonnative feral goats in Hawaiian dryland montane landscapes

Background/Question/Methods

Large populations of nonnative, feral goats (Capra hircus) are present on five of the eight main Hawaiian Islands where they have been notable components of the landscape for at least a century. However, very little information exists on their behavioral ecology (e.g., habitat use, seasonal movement patterns, movement response to vegetation structure and phenology, etc.). Such an understanding is essential to manage not only the goats, but also the native plant communities that they inhabit. The objectives of the current study were to determine: (i) what plant communities feral goats prefer in Hawaiian montane dry forest, and  (ii) if feral goats respond to intra-seasonal vegetation dynamics on small temporal scales. We deployed GPS satellite collars (n=12) to track movement patterns of feral goats every two hours over a one year period in one of the last remaining, relatively intact montane dry forest habitats on the Island of Hawai‘i. Movement data was retrieved remotely from collars and combined with land cover data and remotely sensed imagery (NASA’s MODIS sensor; Carnegie Airborne Observatory LiDAR) to quantify how movement patterns are correlated with plant community composition and seasonal changes in vegetation dynamics (structure, composition, and phenology).

Results/Conclusions

A Euclidean distance-based analysis revealed significant differences in habitat use based on plant community composition, time of day, time of year, and sex. Results of this work indicate that feral goats did not use habitat uniformly, but rather showed preference for native-dominated shrublands during the day and barren lava at night. Males generally had larger home ranges (27.8 km²) than females (12.8 km²), and males demonstrated more frequent fission and fusion behavior between herds. Displacement data demonstrated a bimodal diurnal pattern of activity and habitat utilization, where feral goats tended to be more active during crepuscular times. Displacement data also suggested that three movement phases can be identified: (i) resting; (ii) searching; and (iii) foraging. Ultimately, the results of this study can be used in the context of both the conservation and restoration of native Hawaiian dry forest ecosystems, arguably the most degraded ecosystem in the Hawaiian Islands, if not the world.