Himalayan birds that show the greatest elevational shifts remain within the narrowest thermal regimes

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Abstract
Aim: Elevational migration is a globally ubiquitous animal behaviour. Understanding the mechanisms that drive variation in elevational movement can help explain the evolution of this widespread animal behaviour and its role in shaping montane life history. We examine the role of thermal regime (the intra‐annual variation in temperature experienced by a species), dispersal ability and diet in explaining the extent of elevational movements.Location: Eastern and Western Himalayas.Time Period: 2011–2022.Major Taxa Studied: Birds.Methods: We used community science data from eBird to acquire checklist‐based observations of birds and used comprehensive data cleaning procedures and randomization tests to produce estimates of seasonal elevational shifts for 302 species of Himalayan birds. Using these data, we ran phylogenetic least squares regressions (PGLS) to test if the extent of elevational shift is driven by thermal regime, dispersal ability and diet.Results: Most Himalayan birds (up to 65%) showed downslope shifts in the winter, although some (5%‐10%) low elevation species shifted upslope. Elevational shift was negatively associated with a species' thermal regime. Species that showed the greatest elevational shifts in both eastern and western Himalayas moved within the narrowest intra‐annual temperature regimes, but did not match their breeding range temperatures as closely as possible. Diet influenced elevational shift in both eastern and western Himalayas, while dispersal ability did not drive elevational shifts.Main Conclusions: Species that show the biggest elevational shifts track thermal regimes most closely. However, in addition to tracking thermal regimes, diet and potentially habitat availability/preferences may drive seasonal elevational shifts. Our results show convergent evolution of elevational shifts across clades. Low elevation habitats are important not only for conserving low elevation birds but also for conserving wintering sites of most high elevation breeders.

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