Effects of grassland degradation on bird communities in the Zoige alpine grassland on the eastern Qinghai-Xizang Plateau

Grasslands sustain vital ecosystem services and represent key reservoirs of biodiversity and global biogeochemical processes. Under the combined pressures of climate change and anthropogenic disturbance, alpine grasslands in China have undergone widespread degradation, yet the ecological consequences for avian assemblages remain poorly resolved. To address this knowledge gap, bird surveys were conducted across four degraded grassland types in the Zoige alpine region on the eastern Qinghai-Xizang Plateau during May, July, and September of 2018 and 2019. A total of 40 bird species were recorded, dominated by small omnivorous passerines. Patterns of bird diversity were complex: lightly and moderately degraded grasslands exhibited reduced taxonomic diversity but elevated phylogenetic and functional diversity, whereas original and severely degraded grasslands supported higher taxonomic diversity but lower phylogenetic and functional diversity. Community structure was strongly shaped by dominant species such as Onychostruthus taczanowskii, which disproportionately influenced assemblage composition. These findings demonstrate that multidimensional avian diversity did not decline monotonically with increasing grassland degradation, and shifts in dominance, community complexity, and stability provide sensitive indicators of ecological change in Zoige alpine grasslands.