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.尽管利用光敏地理定位器（light-sensitive geolocators）追踪动物移动轨迹、刻画迁徙连通性（migratory connectivity）模式具备显著优势，但学界已针对这类装置的负面影响提出担忧，尤其聚焦于小型空中食虫鸟类类群。这类地理定位器可能成为额外负担，提升受试个体的能量消耗，这或可解释已有研究中地理定位器对鸟类存活率产生的影响。本研究针对采自北美与欧洲的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）”：以装置佩戴后新生羽毛中的皮质酮（corticosterone，CORTf）水平作为能量相关生理状态的衡量指标。与研究预测相悖的是，无论是两种燕类的群体间水平（两类燕均纳入分析），还是个体内水平（仅树燕种群），羽毛皮质酮水平均未因佩戴装置出现显著差异。因此，若羽毛皮质酮水平能够反映机体能量消耗情况，则对于佩戴定位器后成功回迁的鸟类而言，光敏地理定位器并未构成显著的额外负担。尽管这一生理学证据表明，从佩戴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，但我们仍无法排除皮质酮在已有研究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相关联。