Abstract

Montane ecosystems contribute significantly to global diversity, serving as refuges for numerous species, many of which are entirely restricted to mountainous areas. These species are particularly vulnerable to anthropogenic stressors, which are expected to result in heterogeneous shifts in elevational distributions and potential range restrictions. Here, we resurveyed the elevational ranges of birds in Tianmu Mountain, eastern China, in 2021, 60 years after the original survey in the 1960s. We aimed to determine whether the elevational shifting trends of birds in the lowland and highland regions are asynchronous and whether these trends can be predicted by species traits. Over the past 60 years, we observed the upward shifts of the upper limit of lowland birds, exhibiting range expansion. However, highland birds have generally contracted their upper limits downward, resulting in decreased range. Upslope shifts and range expansions were more pronounced in species with smaller range sizes, while widely distributed species were more likely to move downward and lose occupancy of elevational areas. Our results illustrate the heterogeneous elevational range shifts between two lowland and highland bird assemblages, highlighting the complexity of avian responses to environmental changes and the need for caution when applying conventional patterns of elevational upslope shifts to species redistribution in montane ecosystems.