Data from: Seasonal patterns in δ2H values of multiple tissues from Andean birds provide insights into elevational migration

Elevational migration is a widespread phenomenon in tropical avifauna but it is difficult to identify using traditional approaches. Hydrogen isotope (δ2H) values of precipitation decrease with elevation so δ2H analysis of multiple bird tissues with different isotopic incorporation rates may be a reliable method for characterizing seasonal elevational migration. Here we compare δ2H values in metabolically inert (feathers and claws) and metabolically active (whole blood) tissues to examine whether an upslope migration occurs prior to the breeding season in the Yungas Manakin (Chiroxiphia boliviana). We compare results from C. boliviana with data from a known elevational migrant, the Streak-necked Flycatcher (Mionectes striaticollis). Opposite to our expectations, tissue δ2H values increased over time, largely reflecting seasonal patterns in precipitation δ2H rather than elevational effects; linear mixed-effects models with strongest support included ordinal date, tissue type and elevation. This seasonal increase in precipitation δ2H is a general phenomenon in both tropical and temperate mountain ranges. We use these data to propose a hypothetical framework that predicts different patterns in tissue δ2H values collected in different seasons from residents and elevational migrants. This framework can serve as a reference for future studies that assess elevational migration in birds and other animals.海拔迁徙是热带鸟类区系中广泛存在的现象，但传统研究方法难以对其实现有效识别。降水的氢同位素（Hydrogen isotope，δ²H）值随海拔升高逐渐降低，因此针对具有不同同位素掺入速率的多种鸟类组织开展δ²H分析，或可成为表征季节性海拔迁徙的可靠手段。本研究对比了代谢惰性组织（metabolically inert，即羽毛与爪）与代谢活性组织（metabolically active，即全血）中的δ²H值，以探究永加斯伞雀（Chiroxiphia boliviana）是否在繁殖季前存在上坡迁徙行为。我们将玻利维亚伞雀（C. boliviana）的研究结果与已知海拔迁徙物种——纹颈霸鹟（Mionectes striaticollis）的相关数据进行了比对。与我们的预期相悖，组织的δ²H值随时间推移呈上升趋势，这在很大程度上反映了降水δ²H的季节变化模式，而非海拔效应；最优拟合的线性混合效应模型（linear mixed-effects models）包含序日期、组织类型与海拔三个变量。降水δ²H的这种季节性上升现象，在热带与温带山地均普遍存在。本研究基于上述数据提出了一个假说框架，该框架可预测居留型鸟类与海拔迁徙型鸟类在不同季节采集的组织δ²H值所呈现的差异模式。该框架可为未来评估鸟类及其他动物的海拔迁徙行为的相关研究提供参考依据。