Ecological traits affect the seasonal migration patterns of breeding birds along a subtropical altitudinal gradient

Abstract

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. To explore the potential drivers of seasonal altitudinal migration for birds in the middle of Hengduan Mountains, we conducted a three-year investigation on breeding and non-breeding season bird communities at eight elevational bands (1200–4200 ​m) in the Gongga Mountains. We examined the altitudinal migration patterns and relationships between seasonal distribution shifts and species' traits of 50 species with sufficient data recorded in both seasons. We found that a large proportion of breeding birds underwent altitudinal migration and showed three migration patterns (downslope shift, upslope shift, no shift). Seasonal distribution shifts were mainly correlated with certain ecological traits. Species breeding at high and mid-elevations, nesting in scrub and being omnivorous are more likely to show downslope movements during the non-breeding season. In addition, territorially weaker species exhibited more diverse migration patterns. Notably, we found the hand-wing index (HWI) was actually more convincing than body mass in explaining altitudinal migration. These results consolidate the studies of seasonal altitudinal migration in montane birds. Our study could be used to bridge existing knowledge gaps that currently impeding effective conservation for montane avifaunas in the Hengduan Mountains.

Keywords

• Altitudinal migrant
• Breeding birds
• Functional traits
• Gongga mountain
• Migration patterns