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）追踪动物运动、描述迁徙连通性模式具有诸多优势，但这类装置的负面影响仍引发了学界的广泛担忧，尤其针对小型食虫飞鸟类群。地理定位器可能成为加重机体能量消耗的生理累赘，这或可解释已有研究中报道的地理定位器对鸟类存活产生的影响效应。我们针对北美与欧洲的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）：以装置部署后新生羽毛中的皮质酮（corticosterone，简称CORTf）水平作为能量代谢相关生理状态的量化指标。研究结果与预期相悖：无论是跨种群比较（两个物种均呈现此结果），还是个体内水平分析（仅针对树燕），羽毛皮质酮水平均未随地理定位器的佩戴情况出现显著差异。因此，若羽毛皮质酮水平能够反映机体能量消耗状况，那么对于装置部署后成功回迁的个体而言，地理定位器显然并未构成显著的生理负担。尽管这一生理学证据表明，通过佩戴地理定位器并成功回迁的燕类所获取的迁徙相关数据，并未受到应激水平的系统性偏倚，但我们仍无法排除皮质酮参与介导地理定位器对鸟类存活产生影响的可能性；同时建议未来研究可将皮质酮与繁殖历史等前置影响因素，以及下游适合度代价相关联。