Seasonal variation in the dependence of avian order composition on vegetation characteristics: A case study from Heilongjiang Province, northernmost China

Although bird dependence on vegetation is well established, its seasonal variation remains poorly understood, particularly in high-latitude cold regions. Based on citizen science data from the China Bird Report (CBR), this study investigated the seasonal variation in the effects of vegetation characteristics on avian order composition in Heilongjiang Province, the northernmost in China. The study period was divided according to vegetation phenology into a growing season and a dormant season, which were analyzed separately. We first combined permutation-based multivariate analysis of variance (PERMANOVA) with non-metric multidimensional scaling (NMDS) to test whether bird order composition differed between the two seasonal periods. Then random forest (RF) regression models were applied to further explore the importance of bird orders in predicting vegetation characteristics and generated partial dependence plots to visualize these relationships. The results revealed pronounced seasonal differences. Specifically: (1) during the growing season, open understory vegetation promoted the diversity of birds with different ecological habits, whereas dense, well-developed multilayered vegetation facilitated trophic interactions between raptors and small forest birds; (2) during the dormant season, tall trees provided favorable resources for some Accipitriformes and Anseriformes , and dense evergreen terrestrial vegetation offered essential overwintering resource for Strigiformes ; and (3) across seasons, the effective maintenance of wetland vegetation were crucial for sustaining waterbird diversity, while the retention of mature trees within moderately dense forests supported the abundance of Piciformes . These findings highlight pronounced phenological differences in bird–vegetation interactions and offer new insights for bird conservation and vegetation planning in cold-region ecosystems. • Different bird orders show markedly different dependencies on vegetation characteristics between different seasonal periods. • During the growing season, open understory vegetation strongly promotes the diversity of waterbirds, shorebirds, ground-feeding birds and forest birds. • Multilayered dense vegetation supports food chains for raptors ( Accipitriformes , Falconiformes ) and insectivorous forest birds ( Coraciiformes ). • In the dormant season, tall trees support Accipitriformes and Anseriformes , while evergreen vegetation is essential for overwintering Strigiformes. • Across seasons, effective wetland vegetation management and maintaining sufficient mature woodland trees help sustain waterbird diversity and abundant Piciformes.