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 insectivores. 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.尽管光敏地理定位器（light-sensitive geolocators）在追踪动物活动、刻画迁徙连通模式方面具备显著优势，但学界已针对这类设备的负面影响提出担忧，尤其聚焦于小型空中食虫动物类群。地理定位器可能成为增加能量消耗的生理累赘，这或可解释已有研究中地理定位器对鸟类存活产生的影响。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）”；以设备部署后新生羽毛中的皮质酮（corticosterone, CORTf）水平作为能量代谢相关生理状态的衡量指标。与预期相悖的是，无论跨种群水平（两个物种均呈现此结果）还是个体内水平（仅针对树燕），羽毛皮质酮水平均未因佩戴设备产生显著差异。因此，若羽毛皮质酮水平能够反映能量消耗情况，则对于设备部署后成功回迁的鸟类而言，地理定位器并未构成显著的生理累赘。尽管此项生理证据表明，从佩戴地理定位器并成功回迁的燕类身上获取的迁徙相关数据，在应激水平层面不存在偏倚，但我们仍不能排除皮质酮在已有研究中与鸟类存活受地理定位器影响相关的可能性；同时建议未来研究可将皮质酮与繁殖历史等前置因素，以及后续的适合度代价相关联。