Seasonal variation in community composition and distributional ranges of birds along a subtropical elevation gradient in China

Aim Seasonal variation in community composition and species distributional
ranges along elevational gradients remain poorly known but are essential
to inform conservation. In this study, we aim to understand how species
richness, community composition, and elevational ranges of montane birds
change between the breeding and the non-breeding season. Location The east
slope of the southern Gaoligong Mountains, Yunnan, southwestern China,
elevational range: 700 - 3400 m a.s.l.; latitudinal range: 24°56´- 26°09´
N. Methods We compared bird species richness and community composition in
nine 300-m elevational bands in the breeding (April - May) and
non-breeding (December - January) seasons. We also calculated seasonal
elevational shifts of 97 species with sufficient data recorded in both
seasons and assessed how species’ traits influenced these shifts. Results
Species richness declined in high and low elevations between the breeding
and non-breeding season. The temporal beta diversity shift from the
breeding to the non-breeding season was mainly caused by species losses
rather than species gains in high- and low- elevation communities.
Communities in middle elevations showed a contrasting pattern, with
seasonal composition change resulting mainly from species gains. We also
found that species’ seasonal distribution shifts were mainly associated
with breeding elevation and diet. Notably, high- and middle-elevation
breeders and insectivores significantly shifted their elevational ranges
downslope in the non-breeding season. In addition, species that
participate in mixed-species flocks and that rely on forests also showed
significant downslope shifts in the non-breeding season. Main Conclusions
These results show complex patterns of the interconnectedness of bird
communities along the elevational gradient. Keeping forests at middle
elevations intact appears especially important as they are used in winter
by species that breed at both high and middle elevations. Furthermore, our
results suggested conservation actions maintaining connectedness in low
and middle elevations are urgently needed to conserve regional
biodiversity and highlight the importance of seasonality in montane
ecosystem research.