Taiwan's Breeding Bird Survey reveals very few declining species

Abstract

Multi-species indicators (MSIs) have been useful tools for reflecting the state of taxa and ecosystems at global, regional, and national levels. However, most indicators are from Europe and North America, and there are few from the world’s major tropical and subtropical biodiversity hotspots, often in large part because of insufficient data availability. We modelled the population trajectories of 107 regularly-occurring breeding bird species in Taiwan (100 native and seven introduced species) and developed MSIs for (i) forest, (ii) farmland, and (iii) introduced bird species based on the Taiwan Breeding Bird Survey dataset between 2011 and 2019. Individual population trajectories for 87 species did not show a significant change, those for 11 species grew significantly, and those for two species declined significantly. All MSIs show significant growth. Based on the phylogenetic generalised least squares (PGLS) results, the forest bird indicator increased somewhat more rapidly than the farmland bird indicator, perhaps reflecting very low rates of deforestation contrasting with more rapid land use change on farmlands in Taiwan. Some of the forest and farmland species, however, showed rapid declines, and most of these atypical decliners were common species or carnivores. Further, the PLGS results show that the introduced species indicator had more rapid growth than native species indicators, posing a potential risk for the integrity of native bird communities in the near future as well as compromising broader ecosystem intactness. Our study provides important information on bird population changes in subtropical Asia. The MSIs will be updated regularly and will be used to provide information to support conservation policies in Taiwan.