Integrating long-term bird observation data with landscape connectivity for conservation network: a case study of the Yangtze River Delta, China

The accelerated expansion of high-density urban agglomerations driven by global urbanization poses a severe threat to avian migratory networks. Focusing on the Yangtze River Delta (YRD) region of China as a representative case, this study integrated 116,102 time-series bird observation records collected over 15 years with multi-source remote sensing data, and coupled them with a three-dimensional landscape resistance model. This approach revealed the mechanisms by which urbanization degrades bird habitats and migratory routes, and further simulated optimized multi-level conservation network scenarios. The results indicated that: (1) Between 2010 and 2019, urban expansion in the YRD led to a drastic 61.39% reduction in highly suitable habitats for birds, exhibiting a cliff-like decline; although partial recovery occurred during 2020–2024, the net loss over the entire 15-year period remained substantial. (2) Vertical barriers intensified ecological corridor fragmentation, with current density within high-rise zones decreasing by up to 89%, reducing the total number of ecological corridors from 556 to 459 and causing a 35.3% decline in patch connectivity. (3) The existing protected area system neglects the vertical requirements of migratory birds, as a 211% increase in the number of buildings taller than 50 m around protected areas compelled birds to fly at considerably higher altitudes. (4) Simulations of three scenarios (status quo maintenance, bird habitat conservation, and urban expansion balance) showed that the collaborative conservation framework, which includes reinforcing the core habitats, rebuilding resilient corridors, and supplementing urban ecological functions, was more effective. By transcending the limitations of traditional two-dimensional analyses, this study leveraged dynamic data to uncover cumulative thresholds of habitat degradation and the compensatory potential of semi-natural habitats, thereby providing theoretical insights for constructing avian ecological networks in highly urbanized regions worldwide.