Effects of grassland degradation on the bird community in the Zoige alpine grasslands on the eastern Qinghai-Tibetan plateau

Grasslands provide important ecosystem services and are crucial for conserving biodiversity and global biogeochemical cycles. However, due to climate change and human disturbance, alpine grasslands in China have degenerated to different degrees. Exploring the impact of grassland degradation on bird community is of great significance, as birds in the alpine grassland ecosystem are sensitive to the environmental changes. We conducted bird surveys in four different types of degraded grassland in Zoige alpine grassland on the eastern Qinghai-Tibetan Plateau in May, July, and September of 2018 and 2019, and recorded 40 bird species in total with the majority being small-sized omnivorous passerine species. The effect of grassland degradation on bird diversity was complex: Bird community compositions in lightly degraded grassland and moderately degraded were most similar with lower taxonomic diversity but higher phylogenetic and functional diversity. Original grassland and severely degraded grassland had greater taxonomic diversity but lower phylogenetic and functional diversity. Besides, the dominant species (e.g., Onychostruthus taczanowskii) contributed greatly to the variation of bird community composition. Our research found that the multidimensional bird diversity did not monotonically decrease with the increase of grassland degradation, and dominant species and community complexity and stability can reflect bird community changes in Zoige alpine grassland.