Data from: Experimental effects of early-life corticosterone on the HPA axis and pre-migratory behaviour in a wild songbird

1.Although laboratory studies have shown that chronic exposure to elevated glucocorticoids during development can have profound effects on the physiology and behaviour of animals, we still have a poor understanding of the proximate and ultimate consequences of early-life stress on individuals in the wild. 2. In an island population of Savannah sparrows (Passerculus sandwichensis), we examined multiple hypotheses to explain how elevated glucocorticoid exposure during the nestling period influenced both hypothalamic-pituitary-adrenal (HPA) axis function during the nestling period and the subsequent movement and survival of young after they fledged the nest. 3. We exposed nestlings to exogenous corticosterone from 2-6 d of age and then measured both baseline and stress-induced (30 min restraint) plasma corticosterone levels prior to fledging (d 7). We then recaptured young throughout the pre-migratory period and used mark-recapture analysis to estimate temporary emigration from the capture site (movement) and survival. 4. Corticosterone-treated nestlings had higher baseline corticosterone levels and lower stress reactivity than untreated individuals, and were more sensitive to inclement weather. Although there was no evidence that corticosterone treatments influenced survival, treated individuals had higher rates of temporary emigration outside of the study site than sham or controls. 5. Our results provide support for the ceiling hypothesis, which suggests that individuals with chronic elevated glucocorticoids can lead to a dampened HPA axis response. We also provide support for the CORT-activity hypothesis, which suggests that elevated glucocorticoids can increase activity levels, at least 1-2 months after leaving the nest. Our study highlights the importance of tracking individuals across multiple stages of the annual cycle to understand how early life events carry-over to influence both physiology and behaviour.

1. 尽管实验室研究已证实，发育过程中长期暴露于升高的糖皮质激素（glucocorticoids）会对动物的生理与行为产生深远影响，但我们对野生个体早期生活应激所产生的近因与终极后果仍知之甚少。
2. 本研究以萨凡纳草鹀（Passerculus sandwichensis）的岛屿种群为研究对象，通过检验多个假说，旨在阐明育雏期糖皮质激素暴露升高如何同时影响育雏期的下丘脑-垂体-肾上腺（HPA）轴功能，以及幼鸟离巢后的后续移动与存活情况。
3. 我们对2至6日龄的幼鸟施加外源性皮质酮（corticosterone），随后在离巢前（第7日）分别测定其基础血浆皮质酮水平与应激诱导（30分钟束缚）的血浆皮质酮水平。之后在整个迁徙前阶段对幼鸟进行重捕，并通过标记重捕分析法估算其从捕获位点的暂时迁出（移动）情况与存活率。
4. 经皮质酮处理的幼鸟，其基础皮质酮水平高于未处理个体，且应激反应性更低，同时对恶劣天气更为敏感。尽管未发现皮质酮处理对存活率存在影响，但处理组幼鸟从研究位点向外暂时迁出的比率显著高于假处理组与对照组。
5. 本研究结果支持上限假说——该假说提出，长期糖皮质激素水平升高的个体，其HPA轴响应会被减弱。同时，本研究也为皮质酮-活性假说提供了支持：该假说认为，糖皮质激素水平升高会提升个体的活动水平，至少在离巢后的1至2个月内如此。本研究强调，若要阐明早期生活事件如何通过遗留效应影响生理与行为，需对个体在年度周期的多个阶段进行追踪监测。