Data from: Assessing costs of carrying geolocators using feather corticosterone in two species of aerial insectivore

Despite benefits of using light-sensitive geolocators to track animal movements and describe patterns of migratory connectivity, concerns have been raised about negative effects of these devices, particularly in small species of aerial insectivore. Geolocators may act as handicaps that increase energetic expenditure, which could explain reported effects of geolocators on survival. We tested this ‘Energetic Expenditure Hypothesis’ in 12 populations of tree swallows (Tachycineta bicolor) and barn swallows (Hirundo rustica) from North America and Europe, using measurements of corticosterone from feathers (CORTf) grown after deployment of geolocators as a measure of physiology relevant to energetics. Contrary to predictions, neither among- (both species) nor within-individual (tree swallows only) levels of CORTf differed with respect to instrumentation. Thus, to the extent that CORTf reflects energetic expenditure, geolocators apparently were not a strong handicap for birds that returned post-deployment. While this physiological evidence suggests that information about migration obtained from returning geolocator-equipped swallows is unbiased with regard to levels of stress, we cannot discount the possibility that corticosterone played a role in reported effects of geolocators on survival in birds, and suggest that future studies relate corticosterone to antecedent factors, such as reproductive history, and to downstream fitness costs.尽管使用光敏地理定位器（light-sensitive geolocators）追踪动物活动、描绘迁徙连通性（migratory connectivity）格局具有诸多优势，但学界已针对这类设备的负面影响提出质疑，尤其针对小型食虫飞禽（aerial insectivore）类群。地理定位器可能成为生理累赘，增加机体能量消耗（energetic expenditure），这或许可以解释此前报道的地理定位器对鸟类存活率的影响。我们针对来自北美与欧洲的12个树燕（Tachycineta bicolor）和家燕（Hirundo rustica）种群，检验了这一“能量消耗假说（Energetic Expenditure Hypothesis）”：以佩戴地理定位器后新生羽毛中的皮质酮（corticosterone）水平——即羽毛皮质酮（CORTf）——作为能量代谢相关的生理学指标。与研究预测相悖的是，无论是跨物种层面（两种燕类）还是个体内层面（仅树燕），CORTf水平均未因佩戴装置出现显著差异。因此，若CORTf能够反映机体能量消耗，那么对于佩戴设备后成功返回的鸟类而言，地理定位器并未构成显著的生理累赘。尽管此项生理学证据表明，从佩戴地理定位器并成功返回的燕类中获取的迁徙相关数据，在应激水平维度不存在偏差，但我们仍无法排除皮质酮在已报道的地理定位器对鸟类存活率的影响中发挥作用的可能性，并建议未来研究可将皮质酮与繁殖历史等前置因素，以及后续适合度成本（fitness costs）相关联。