Context-dependent effects of land-sparing and land-sharing strategies on urban bird diversity

Urban green spaces play a vital role in sustaining biodiversity, particularly bird communities, in rapidly urbanizing regions. Two contrasting land-use strategies—land sparing (LSP) and land sharing (LSH)—have been proposed to reconcile urban development with biodiversity conservation, yet their relative benefits remain poorly understood across gradients of green-space cover, seasonal dynamics, and species groups. This study aims to compare the effects of LSP and LSH on urban bird diversity and explore how green-cover gradients, bird residency status (resident vs. migratory), and seasonal periods (breeding vs. non-breeding) influence the biodiversity outcomes of the two land-use strategies. Using Nanjing, China, a highly urbanized city along the East Asian-Australasian Flyway, as a case study, we collected 116,387 citizen-science bird records from 2022 to 2024. Avian diversity was quantified using species richness, Shannon–Wiener, and Simpson indices, which were subsequently integrated through principal component analysis. Diversity was compared across three spatial scales (500, 1000, and 1500 m), considering green-cover gradients, bird residency status (resident vs. migratory), and seasonal periods (breeding vs. non-breeding). Generalized additive models were applied to identify the key environmental drivers of bird diversity under each strategy. Our study found that LSP tended to be associated with higher avian diversity, especially for resident birds in areas with green cover below 50%, although these patterns were not always statistically significant. In contrast, LSH tended to favor migratory birds under higher green-cover conditions (> 50%) and during the non-breeding season. Differences between the two strategies were most clearly expressed at the 500 m scale. Human disturbance, especially the Human Footprint Index, was one of the most frequently identified predictors of avian diversity under both strategies. Our results suggest that the biodiversity outcomes of urban LSP and LSH cannot be generalized without accounting for green-space cover, season dynamics, and species residency status, providing an analytical framework that can be adapted to evaluate biodiversity-sensitive planning in other rapidly urbanizing cities.