Objective In lake ecosystems, islands, as isolated terrestrial areas and stepping-stone habitats, are scarce yet high-quality habitats for birds, especially waterbirds, providing them with suitable environments for resting, breeding, and foraging. The construction and habitat optimization of lake islands are effective means to promote the conservation of waterbirds and enhance wetland biodiversity. Currently, research on urban lake islands remains limited, particularly regarding the relationships among spatial configuration, habitat characteristics, and bird diversity. This research aims to assess the effectiveness and ecological impact of the habitat optimization design of the island in Xinglong Lake, explore the relationship between bird diversity and island habitat structure, and provide a scientific basis and replicable design framework for improving habitat quality on artificial islands in urban lake ecosystems.

Methods Concentrating on three key island spatial categories: Island interior, island shoreline, surrounding waters, this research selects waterbirds as indicator tax, and takes Xinglong Lake’s island in Tianfu New Area, Sichuan as the main research object. Field survey is conducted to document species composition, abundance, spatial distribution patterns, and habitat conditions of bird communities. To assess the ecological outcomes of habitat optimization, comparative analyses are performed using three control sites within the Chengdu metropolitan area: Jincheng Lake’s island and Qinglong Lake’s island (both exhibiting similar natural setting, while differing in morphology and lacking ecological restoration), as well as Qinhuang Lake (containing no constructed islands). Habitat classification and mapping are carried out through GIS-based spatial analysis and habitat unit delineation, following standardized protocols from the urban habitats biodiversity assessment (UHBA) standard and the urban habitat categories (UHCs) classification system. Island habitats are systematically categorized, visualized, and quantified to investigate the relationship between habitat structure and bird community attributes. This approach enables the identification of key habitat variables influencing bird diversity and the underlying ecological mechanisms driving relevant habitat patterns.

Results According to the UHCs system, a total of 12 habitat types are identified across all research sites. The restored Xinglong Lake’s island exhibits the highest habitat diversity, comprising 11 distinct types, compared to 8 and 4 types recorded on Qinglong Lake’s island and Jincheng Lake’s island, respectively. The restored island also displays more complex habitat structures and element assemblages, forming a nested spatial mosaic of habitat types across vertical and horizontal gradients — from the island’s interior to its shoreline and adjacent waters. By constructing diverse composite habitat structures such as dense forests, sparse forests – grasslands, sparse forests – meadows, forests – ponds, micro-wetland, island shoreline grasses, grasslands, fallen logs, dead branches, bare soil, and island surrounding waters forests – swamps along waters surrounding the island, grasses –swamps, shrubs – grass swamps, shallows, and deep pools – shallows, Xinglong Lake has formed a composite pattern of alternating habitat types, providing key support for different bird community types. The contagion index, dispersion index and aggregation index further verify the highly mosaic habitat pattern and high habitat heterogeneity of Xinglong Lake’s island. The habitat diversity index (DIVh = 2.043) of Xinglong Lake’s island is significantly higher than that of Jincheng Lake’s island (DIVh = 0.883) and Qinglong Lake’s island (DIVh = 1.188). A total of 26 bird species (14, 510 birds in total, Dmg = 2.61) are recorded on Xinglong Lake’s island, where many birds are attracted, including the Aythya baeri (a critically endangered CR bird species identified by IUCN and listed as a national first-class protected bird in the “National Key Protected Wildlife List”), significantly more than the control group’s 13 species (1, 984 birds in total). The ecological restoration strategy for Xinglong Lake’s island based on the key spatial categories of “island interior – island shoreline – surrounding waters” can effectively optimize the island’s spatial configuration, and enhance its habitat diversity and heterogeneity, while providing essential functional habitats for waterbirds’ nesting, breeding and foraging. Waterbird diversity on the restored island is significantly higher than that observed at the control sites, demonstrating notable ecological restoration benefits. Pearson correlation analysis shows that waterbird diversity has no significant correlation with lake area or general lake-scale indicators, indicating minimal interference from lake size. Island area, water depth gradient around the island, and the types, forms and structures of island habitats are core variables affecting waterbird diversity. These findings highlight the importance of habitat spatial heterogeneity and effective niche construction as primary mechanisms driving the enhancement of waterbird diversity in urban lakes.

Conclusion The ecological restoration strategies implemented on Xinglong Lake’s island have provided crucial functional habitats for waterbirds that can support nesting, breeding, and foraging activities, thus being able to effectively enhance the bird diversity of urban lakes. Habitat optimization strategies for urban lake islands, designed based on “topography – vegetation” coordination, “forest – water” composite habitats, and “underwater topography reshaping with food web construction”, have significantly enriched island habitat heterogeneity and improved spatial configuration. Research on the internal mechanisms of “habitat structure – habitat configuration – bird diversity” provides a scientific basis for the design and optimization of waterbird habitats on artificial islands in urban lakes. The aforesaid findings may offer scientific guidance and establish a replicable and promotable innovative technical paradigm for ecological restoration and biodiversity conservation of urban lakes.