Nonlinear effects of vegetation attributes on bird feeding guilds in urban green spaces: Implications for conservation strategies

Urbanization homogenizes habitats, threatening avian functional diversity. Urban parks, as critical refugia, sustain various bird communities through heterogeneous vegetation structure. However, the guild-specific responses to vegetation attributes remain poorly quantified, thus undermining targeted conservation strategies. Therefore, we conducted fine-scale surveys in 60 plots across six urban parks in Zhengzhou, to quantify the relationships between bird biodiversity and heterogeneous vegetation attributes. Bird communities were classified into insectivores, omnivores, and carnivores; concurrently, vegetation functionality was quantified through 12 metrics grouped into three novel dimensions—resource availability, structural suitability, and community composition—while accounting for landscape-level constraints. We proposed three core hypotheses and applied Spearman correlation analysis, the Boosted Regression Tree (BRT) and accumulated local effect (ALE) models. Results show that: (1) Wetlands sustained peak diversity for omnivores and insectivores, while lawns maximized insectivore abundance. (2) Vegetation structural suitability was identified as the most critical dimension for both omnivores and insectivores. (3) The relative contribution of vegetation attributes differed across bird feeding guilds: while average tree diameter at breast height (ATDBH), tree density (TD), and average herbaceous plant height (AHH) were shared key drivers, average herbaceous plant cover (AHC) and average leaf area index (ALAI) were additional key factors affecting omnivores, whereas average tree height (ATH) was a specific important predictor for insectivores. (4) The influence of key drivers generally exhibited nonlinear patterns characterized by distinct optimal intervals. The current study presents a quantitative management framework emphasizing guild-specific interventions to compensate park size constraints and enhance bird diversity.