DISTRIBUTION OF BIRDS IN A HETEROGENEOUS TROPICAL PACIFIC ISLAND FOREST AUTHOR: Isaac Natanael Aguilar ABSTRACT: Invasive species are one of the largest threats to global biodiversity and islands are particularly susceptible. Birds are a model biological indicator of forest ecosystem function because they respond rapidly to environmental change. The forests on Moorea, French Polynesia have been changing rapidly since human arrival and European colonization. I conducted point-count surveys throughout the Opunohu Valley to provide insight on the distribution of endemic and introduced birds. Avifauna abundance and composition differed significantly between native, Polynesian-introduced, and European-introduced canopy sites, revealing differences in habitat suitability. Vegetation cover, elevation, and avifaunal distribution were used to inform a habitat suitability model for endemic avifauna. Together, the results indicate that both native and Polynesian-introduced trees provide important habitat for endemic avifauna compared to recent European-introduced trees in the heterogeneous Opunohu Valley forest. The forest includes populations of two threatened endemic birds, the Moorea kingfisher (T. youngi) and grey-green fruit dove (P. purpuratus), and this study suggests that invasive species control, endemic habitat protection, and sustainable natural resource management strategies will be important to protect the endemic avifauna on South Pacific Islands like Moorea. Key words: Aves; invasive species; Moorea, French Polynesia; forest habitat; Todiramphus youngi; Ptilinopus purpuratus; natural resource management; conservation INTRODUCTION Invasive species are the greatest threat to endemic island species and second most significant threat to global biodiversity (Bellard et al. 2016b, 2017). The most recent estimates are that 86% of island endemic extinctions were caused by invasive species (Bellard et al. 2016a). Endemic island species are particularly vulnerable to invasive species because they tend to have relatively small population sizes, low reproductive rates, reduced defensive traits, and restricted distributions (Soares et al. 2021). The arrival of invasive alien species reduces the availability of resources for the native island population. Invasions therefore threaten island ecosystems because resource availability is responsible for the structure and dynamics of ecological systems (Nowlin et al. 2008). Extensive research on systems perturbed by invasive species is necessary for the conservation of native and endemic island species. The ecological impact of invasive species is complex and can be difficult to quantify. Native indicator species can provide insight on the impact of invasive species on the landscape and ecological community. Birds are a model biological indicator of ecosystem function because they respond rapidly to environmental change (Briggs et al. 2013). The island landscape is reciprocally shaped by symbiotic relationships between bird communities (avifauna) and island vegetation that support ecosystem function and productivity (Rodríguez-Rodríguez et al. 2017). Avian pollination is especially important for ecosystem function on islands where pollination limitations 61 Fall 2020 / Perennial
can impact rare plants and forest structure (Sekercioglu 2006, Carlo and Morales 2016). Avian pollination provides insight on the complex coevolutionary history between avifauna and vegetation (Jordano 1987, Guimarães Jr et al. 2011). Endemic bird species share a deep evolutionary relationship with island vegetation and changes to the landscape are likely to impact their population. Anthropogenic land use and change threatens endemic island avifauna and forests have been suggested as potential refuge (ZoBell and Furnas 2017). However, present-day island forests have a heterogeneous community structure with trees of varying origin, including both native and non-native species. A better understanding of how endemic birds navigate modern heterogeneous forests is essential for their conservation and maintaining overall ecosystem function. Historical environmental processes and anthropogenic activity develop a forest’s community structure – here defined as the abundance and distribution of canopy-forming tree species in a forest. The native forests of islands throughout the South Pacific have been rapidly changing since human arrival and European colonization. The main cause of this change is the facilitation of alien species naturalization by anthropogenic natural resource management. The Polynesians were the first inhabitants of the South Pacific and introduced culturally significant species between islands for resource production such as food and raw materials. Polynesian-introduced tree species include the “Mape” or Tahitian chestnut (Inocarpus fagifer), Malay apple (Syszygium malaccense), and candlenut (Aleurites moluccana). Since European arrival, the abundance and diversity of alien species throughout