Large-scale agricultural development has led to a significant reduction in wetland areas, resulting in habitat fragmentation for birds and biodiversity loss. Recently, the implementation of farmland abandonment policies has helped in the restoration of wetland areas. In order to understand the ecological effects of farmland abandonment, this study investigated the bird communities in the Naoli River National Nature Reserve (NRNNR) in the Sanjiang Plain after abandonment. The field surveys (line transect and point count methods) of bird community diversity in the abandoned areas of the NRNNR showed 92 bird species from 37 families and 16 orders, including 4 species of national first-class protected birds and 17 species of national second-class protected birds (accounting for a combined 22.83%). Additionally, the bird community diversity displayed annual variation in individual and species richness over time, and the diversity indices order was 2019 > 2020 > 2018 > 2016 > 2015. Bird species richness and individual abundance were significantly higher in meadow habitats as compared to other habitat types. With prolonged restoration time after farmland withdrawal, the Pielou evenness index of bird communities significantly decreased, while the total number of individual birds significantly increased (p < 0.05). The abandoned time showed a positive impact on waterbird richness, while the longer abandoned duration led to higher waterbird richness. In conclusion, long-term ecological restoration measures revealed a significant enhancement in bird diversity over time.

The red-crowned crane (Grus japonensis) is a flagship species for wetland biodiversity in East Asia. The Songnen Plain is a vital wetland and habitat for rare and endangered birds in Northeast China. However, rapid land use changes have raised urgent concerns about habitat loss and the survival of these populations. We combined 30 years (1990–2020) of field surveys with ensemble species distribution models (SDMs) to analyze the spatio-temporal changes in suitable habitats for all three key life stages—spring migration, breeding, and autumn migration—across the Songnen Plain. We also assessed how well the current protected-area (PA) network covers suitable habitats and identified conservation gaps. Land use type was the most significant predictor of habitat suitability. Over this period, suitable habitats decreased sharply by 60% (spring migration), 72% (breeding), and 76% (autumn migration), with severe fragmentation and a clear northward shift. Core suitable areas are now mainly found within a few nature reserves, including Zhalong, Wuyu’er River, and Xianghai. We identified three significant conservation gaps: Lindian–Anda, Tailai–Dumeng, and Meilisi Daur–Fuyu. Our results show widespread habitat reduction and demonstrate the inadequacy of the current PA network in supporting the long-term survival of red-crowned crane populations. We recommend expanding protections and restoring wetland connectivity within these gaps to maintain critical habitats and improve landscape resilience for this endangered species.