DOI: 10.5061/dryad.rxwdbrv6c
title: Seasonal variation in community composition and distributional ranges of birds along a subtropical elevation gradient in China

description: 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.
description: From April 2016 to December 2020, we conducted avian community
 surveys using standard line transects along the elevational gradient in
 breeding and non-breeding season. We divided nine 300-m elevational bands
 from 700 m a.s.l. (around the lowest elevation in Salween valley) to
 3400 m a.s.l. (the mountain peak). For each elevational band, we located
 two to four transects varying in length, but the total lengths of
 transects in each elevational band were approximately seven km to ensure
 comparable efforts. For the breeding seasons, we conducted our surveys
 eight times in all transects in April and May (i.e., two replicates per
 year) when birds were actively breeding. We conducted non-breeding surveys
 along the same transects in two non-breeding seasons from December 2018 to
 January 2019, and in December 2020.  We used N-mixture
 model structures for our occupancy models and estimated both occurrence
 and detection probability of 97 species in each elevational band in each
 season with temporal replicates.  We determined the upper-elevation limit,
 the lower-elevation limit, and the elevational range size of these 97
 species using these criteria for true absences in elevational bands in
 each season. We then calculated the abundance-weighted mean elevation for
 each species. The seasonal shifts in these four measures for individual
 species were the differences in corresponding values from non-breeding to
 breeding seasons. Thus, positive values of seasonal shifts in the
 upper-elevation limit, the lower-elevation limit, and the
 abundance-weighted mean elevation represent upslope movements, while
 negative values represent downslope movements, and zero represents no
 change. Finally, we assessed how species’ traits
 affected seasonal elevational shifts. Species’ traits included the
 abundance-weighted mean breeding elevation, body mass, diet, flocking
 status, and forest dependency. We classified the 97 species into
 low-elevation (700 - 1600 m a.s.l.), middle-elevation (1600 - 2800 m
 a.s.l.), and high-elevation breeders (2800 - 3400 m a.s.l.) based on their
 abundance-weighted mean elevations recorded in the breeding season. We
 classified the 97 species into low-elevation (700 - 1600 m a.s.l.),
 middle-elevation (1600 - 2800 m a.s.l.), and high-elevation breeders (2800
 - 3400 m a.s.l.) based on their abundance-weighted mean elevations
 recorded in the breeding season. We extracted body mass and dietary groups
 (insectivore, omnivore, plant-seed eater, and frugivore/nectarivore) from
 the Elton traits 1.0 database (Wilman et al., 2014). We extracted flocking
 status (flocking species vs. non-flocking species) from Birds of the World
 (Billerman et al., 2020) and an empirical database of mixed-species bird
 flocks in southwestern China (Zhou et al., 2019). We classified two
 categories of forest dependency (forest birds: medium and high forest
 dependency; and non-forest birds: low forest dependency) provided by
 BirdLife International Data Zone (BirdLife International, 2020).
description: Below are descriptions of each column of the dataset:
 
 id id number Order The Order of each species Common The common name of each species Species The scientific name of each species Best models Codes for best occupancy models for each species. Best model codes were provided in Table S2 WAIC WAIC for the best models for each species Detection (breeding) Detection probability of each species in the breeding season Detection (non-breeding) Detection probability of each species in the non-breeding season Shifts (upper) The shifts in upper-elevational limits. Positive values indicate upslope shifts, negative values indicate downslope shifts, zeros represent no shifts Shifts (mean) The shifts in abundance-weighted mean elevations. Positive values indicate upslope shifts, negative values indicate downslope shifts, zeros represent no change Shifts (lower) The shifts in lower-elevational limits. Positive values indicate upslope shifts, negative values indicate downslope shifts, zeros represent no shifts Shifts (range_size) The shifts in elevational range sizes. Positive values indicate upslope shifts, negative values indicate downslope shifts, zeros represent no shifts Breeding_elevation Three-categorical trait: Mean abundance-weighted breeding elevation for each species. High: 2800 - 3400 m; Middle: 1600 - 2800 m; Low: 700 - 1600 m Flocking Two-categorical trait. Flockors: species that normally join mixed-species flocks in winter; Non-flockors: species that do not normally join mixed-species flocks in winter. Data were collected from Zhou et al. 2019 Condor and Birds of World. Forest_dependent Two-categorical trait. Forest species: species with middle and high forest dependency; Non-forest species: species with low forest dependency based on BirdLife International Data Zone Diet Four-categorical trait: diet groups including Invertebrate, Omnivore, FruiNect, and PlantSeed based on Wilman et al. Ecology 2014 Elton Trait 1.0 Mass Continuous trait: mean body mass of each species from Wilman et al. Ecology 2014 Elton Trait 1.0