Assessment of Habitat Change for the Critically Endangered Kiwikiu

Abstract

The kiwikiu (Maui Parrotbill; Pseudonestor xanthophrys) is a critically endangered Hawaiian honeycreeper with fewer than 200 estimated individuals remaining in 30km2 of high-elevation native forest in East Maui. Kiwikiu have experienced vast historical habitat loss and continue to be threatened by predation, disease, non-native species, and associated habitat loss and degradation. The introduced avian malaria disease is currently the primary restriction for kiwikiu range, severely limiting the species’ potential habitat occupancy to higher-elevation forests, with further range restrictions from this threat expected by global climate change. In turn, existing suitable habitat remains highly threatened by non-native invasive plants and ungulates. Therefore, current site-specific habitat assessments are needed to prioritize management actions (e.g., fencing and ungulate management, invasive plant control, outplantings). The primary objective of this project was to document habitat change that occurred over the past 16 years within the Manawainui region of Haleakalā National Park by designing and applying an efficient vegetation survey protocol to pre-existing vegetation plots from a 2005–2006 kiwikiu habitat study. The vegetation survey methodology was designed to accurately and rapidly assess select indicators of preferred kiwikiu habitat identified in the initial study (i.e., community composition and vegetation structure). Vegetation surveys were conducted in July and August of 2022. Habitat variables were analyzed individually in R and via multivariate analyses in PC-ORD to identify changes in habitat over time. Survey results indicated a significant increase in species richness across woody and herbaceous taxa, while non-native plants continue to be minimally distributed within the survey area. Results also showed a significant increase in tree diversity. In contrast, vegetative ground cover decreased significantly. These results indicate substantial habitat recovery due to prolonged low ungulate densities. However, increased understory disturbance indicates recent increases in feral pig activity. To prevent further degradation, the complete removal and exclusion of feral ungulates from Manawainui should be prioritized, allowing for continued large-scale passive restoration. Vegetation surveys should be reconducted at 5–10 year intervals, which will allow continued documentation of habitat recovery necessary to inform management actions for kiwikiu and other forest bird habitat, as well as overall ecosystem health.