Data from: Ambient temperature, body condition and sibling rivalry explain feather corticosterone levels in developing black kites (Milvus migrans)

In birds, the steroid hormone corticosterone (CORT) is considered a major mediator in a number of physiological mechanisms and behaviours critical for the regulation of an organism′s energy balance. However, the question of whether the way in which circulating plasma CORT is incorporated into feathers actually reflects this regulation, and consequently whether feather CORT (CORT-F) measures allow to make inferences on past levels of energetic demands (i.e. allostatic load), remains unclear. While previous studies have yielded promising results, the technique still wants further study and validation in a wider range of bird species, across life history stages and under different ecological situations. Here we tested whether CORT-F levels in a sample of 427 nestling black kites (Milvus migrans) reflected inter-individual variation in a number of environmental, social and physiological variables known to elevate allostatic load during development. We found that nestlings exposed to low ambient temperatures exhibited high CORT-F, suggesting that feathers registered the expected rise in circulating CORT levels inducing thermogenesis in response to cold stress. CORT-F was also negatively related to body condition, supporting the notion that allostasis becomes less affordable as energy stores become depleted. Finally, CORT-F also reflected brood hierarchy rank, with subordinate chicks exhibiting the highest levels, followed by first-hatched (dominant) chicks and lastly singleton nestlings. Moreover, CORT-F levels in nestlings from multiple-chick broods (but not in singletons) declined with age, mirroring the dynamics of establishment and stabilization of sibling hierarchies in black kites. Altogether, our results underscore the potential of using CORT-F to infer allostatic load in wild avian populations and their potential power as indicator tools in conservation biology.

在鸟类中，类固醇激素皮质酮（corticosterone, CORT）被认为是调控机体能量平衡的多项关键生理机制与行为的核心介导因子。然而，循环血浆皮质酮整合进入羽毛的方式是否真正反映了这一调控过程，以及羽毛皮质酮（feather CORT, CORT-F）检测能否用于推断个体过往的能量需求水平（即稳态负荷，allostatic load），这一问题仍未明确。尽管既往研究已取得颇具前景的成果，但该技术仍需在更广范围的鸟类物种、不同生活史阶段以及各异的生态环境下开展进一步研究与验证。本研究针对427只黑鸢（Milvus migrans）雏鸟的样本展开检测，旨在探究羽毛皮质酮水平是否能反映发育过程中已知会提升稳态负荷的多项环境、社会与生理变量的个体间差异。我们发现，暴露于低环境温度的雏鸟羽毛皮质酮水平更高，表明羽毛可记录因寒冷应激诱导产热而升高的循环皮质酮水平。羽毛皮质酮水平还与身体状况呈负相关，支持了“当能量储备耗尽时，稳态调控的成本会升高”这一观点。最后，羽毛皮质酮水平还能反映窝雏等级：从属雏鸟的皮质酮水平最高，其次是先孵化的优势雏鸟，最后为单雏雏鸟。此外，多雏窝雏鸟（而非单雏个体）的雏鸟羽毛皮质酮水平随日龄增长而下降，这与黑鸢窝内同胞等级的建立与稳定动态相吻合。综上，本研究结果证实了利用羽毛皮质酮推断野生鸟类种群稳态负荷的潜力，以及其作为保护生物学指示工具的应用价值。