While numerous indicators track biodiversity changes in temperate zones, few exist for the tropics, regions of higher biodiversity. Taiwan has seen the emergence of intensive citizen science programs for biodiversity monitoring, particularly focused on birds. This project assesses the population trends of regularly occurring birds in Taiwan, identifies potential threats, and offers conservation strategies. Among breeding birds, 87 native species demonstrated stable populations, 11 species showed significant growth, and two species saw significant declines. The forest bird population indicator increased slightly faster than the farmland bird indicator, reflecting low deforestation rates versus more rapid farmland changes. Some rising indicators contained declining species, emphasizing the need to disaggregate indices. Common and predatory species were atypical decliners. The rapid expansion of introduced species poses a risk to native birds. For migratory waterbirds, population trajectories varied significantly among three regions. Eight species declined significantly in Yi-Lan, four in Chang-Hua, and one in Chia-Nan. Rice paddies loss and building expansion likely drive these declines. Local land use planning policies are crucial for conserving migratory birds, serving as stopover and wintering sites along flyways. This project utilized high-quality biodiversity data in Taiwan to develop subtropical MSIs and understand changing bird populations.