Monitoring of North Island fantail / pīwakawaka fantail (Rhipidura fuliginosa placabilis Bangs, 1921, Rhipiduridae) distribution on Tiritiri Matangi Island: using several spatial methods for processing volunteer data

Abstract

The Aotearoa / New Zealand fantail / pīwakawaka (Rhipidura fuliginosa Sparrman, 1787, Rhipiduridae) is an iconic species and conspicuous in a range of habitats. However, island populations of the species are said to fluctuate dramatically. This project set out to investigate the population dynamics of the Te ika a Maui / North Island subspecies Rhipidura fuliginosa placabilis Bangs, 1921) on Tiritiri Matangi Island using a volunteer-based monitoring scheme. To achieve this goal we developed a pilot sampling grid and determined spatial distribution characteristics using several approaches including geostatistical tools in ArcMap, species distribution modelling and occupancy modelling. Fantail presence data was recorded twice a year by volunteers assigned to specific grids at different seasons for two years on Tiritiri Matangi Island. Recorded count data show distinctive differences between the sampling periods and different areas of the island. Significant hotspots as well as clustering of abundance show different patterns with significantly higher abundance and widespread distribution during May compared to November. Spatial analysis identified vegetation, particularly replanted areas, as influencing the fantail counts. Results of species distribution modelling showed areas of the island suitable for the species and occupancy models further described the seasonal spatial characteristics of fantail. The effort also highlights the importance of volunteers in providing bird count data to generate the knowledge base required for the management of an island sanctuary.