Aim Mountain ecosystems harbour significant biodiversity across elevations and seasons. This biodiversity, however, is increasingly under threat from climate change and human land use. While much work has been done to characterize biodiversity in tropical mountains, far less is known about the environmental, seasonal and spatial factors that impact diversity and community structure in subtropical and temperate regions. Location Mt. Gongga, Sichuan, China: the eastern‐most peak in Asia above 7000‐m elevation and the main peak of the Hengduan Mountains. Method We examined elevational patterns and ecological variables underlying taxonomic diversity (TD), phylogenetic diversity (PD), functional diversity (FD) and community structure in birds on the eastern slope of Mt. Gongga between 1100‐ and 4400‐m elevation. We assessed biodiversity patterns between species with different elevational range sizes (small‐ vs. large‐ranged species) and between seasons (breeding vs. non‐breeding season). Results We recorded 230 bird species across seven field surveys. TD, PD and FD showed similar hump‐shaped elevational patterns in both seasons. In the breeding season, TD, PD and FD for small‐ranged species were highly correlated with climatic factors (mean daily temperature, seasonal temperature range) and vegetation factors (enhanced vegetation index), while large‐ranged species were correlated with spatial factors (mid‐domain effect). In the non‐breeding season, TD, PD and FD for all species groupings were positively correlated with climate factors. For small‐ranged species in both seasons, community structure was more overdispersed at low and high elevations, and more clustered at middle elevations. For large‐ranged species, community structure differed between seasons, showing a general trend towards clustering as elevations increase in the breeding season and trends towards overdispersion and/or evenness as elevations increase in the non‐breeding season. Conclusions We found that different factors shape elevational patterns of diversity for small‐ and large‐ranged species in the breeding season; small‐ranged species are shaped by climate and vegetation structure, while large‐ranged species are shaped by spatial factors. This difference is likely explained by differences in ecological niche breadth (physiological tolerance and/or habitat specialization) between small‐ranged species and large‐ranged species. In the non‐breeding season, however, when climate is seasonally harsher, we found that patterns of diversity for all range‐size groupings were driven by climatic factors. We also found that community structure generally becomes more overdispersed as resource availability decreases and environmental conditions become harsher, like at higher elevations and in the non‐breeding season, suggesting that competition for limited resources is important for shaping communities in seasonal environments. These findings highlight how avian diversity and community structure are dynamic across a local elevational gradient and season...

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Background: Altitudinal bird migration involves seasonal shifts up and down the altitude gradient annually. Asia as the place with the largest number of altitudinal migrants, has quite few related studies, especially for montane and temperate avifaunas.Method: To explore the potential drivers of seasonal altitudinal migration for birds in the middle of Hengduan Mountains, we conducted a two-year investigation on breeding and non-breeding season bird communities at eight altitude sections in the Gongga Mountains. Then, we examined the altitudinal migration patterns and relationships between seasonal distribution shifts and species’ traits, of 20 species with sufficient data recorded in both seasons.Results: We found that a large proportion of resident birds underwent altitudinal migration and showed 3 patterns (downslope shift, upslope shift, no shift). Species’ seasonal distribution shifts were mainly correlated with territoriality, nest height, diet, and temperature tolerance range. The species nesting in scrub and omnivores were more likely to present a downhill movement in the non-breeding season. In addition, territorially weaker species migrated more widely and performed multiple patterns. Notably, HWI dominated upslope shifts in altitudinal migration.Conclusion: Studying the seasonal altitudinal migration patterns of birds is essential to understanding their distributional responses to seasonal changes in climate (energy), which has important conservation implication for avian biodiversity. These results further consolidate the study of seasonal altitudinal migration in montane birds and verify that body mass is not correlated with altitudinal migration. This could be used to bridge existing knowledge gaps that currently impeding effective conservation.