Swiss Ornithological Institute, Seerose 1, 6204 Sempach, Switzerland.
Swiss Ornithological Institute, Seerose 1, 6204 Sempach, Switzerland.
Gen Comp Endocrinol. 2022 Jan 15;316:113946. doi: 10.1016/j.ygcen.2021.113946. Epub 2021 Nov 22.
In birds, feather corticosterone values (CORTf) are increasingly used as a retrospective and integrative proxy of an individual's physiological state during the period of feather growth. Relatively high CORTf values are usually interpreted as an indicator of exposure to energy-demanding or stressful conditions during feather growth. However, in nestlings this interpretation might not always hold true. The reasons are that, firstly nestlings (especially altricial ones) still develop their hypothalamo-pituitary-adrenal (HPA) reactivity during the growth of their feathers. Hence, at a young age, nestlings might be unable to mount a substantial adrenocortical stress response. Secondly, some species are able to down-regulate their metabolism during food scarcity and therewith probably also their CORT release. Consequently, CORTf values may not unambiguously reflect whether nestlings have suffered from energy-demanding or stress situations. Relatively high CORTf values might indicate either energy-demanding or stressful conditions ('stress responsive hypothesis'), or - conversely - favourable conditions during the period of feather growth ('hypo-responsive hypothesis'). In the altricial Alpine swift (Tachymarptis melba), we tested which factors help to distinguish between the two hypotheses by considering factors which affect CORT release (brood size, weather) and factors which are affected by high CORT levels (nestling size and condition). We measured CORTf in 205 nestlings over 7 years and collected data on brood size, body size, body condition and prevailing weather. Nestling CORTf values were positively correlated with body condition and negatively with adverse weather, supporting the hypo-responsive hypothesis. Results from the Alpine swift study, supplemented with a survey of the literature, show that relatively easily collected parameters on brood size, nestling size and condition, and environmental factors can help to distinguish between the two hypotheses. A meaningful interpretation of nestling CORTf should only be made in the context of species-specific traits.
在鸟类中，羽毛皮质酮值（CORTf）越来越多地被用作个体在羽毛生长期间生理状态的回顾性和综合指标。相对较高的 CORTf 值通常被解释为在羽毛生长过程中暴露于能量需求或压力条件下的指标。然而，在巢雏中，这种解释并不总是成立的。原因是，首先，巢雏（尤其是晚成性鸟类）在羽毛生长过程中仍在发育其下丘脑-垂体-肾上腺（HPA）反应性。因此，在年幼时，巢雏可能无法进行实质性的肾上腺皮质应激反应。其次，一些物种在食物匮乏时能够下调其新陈代谢，并且可能也会下调其 CORT 释放。因此，CORTf 值可能无法明确反映巢雏是否经历了能量需求或应激情况。相对较高的 CORTf 值可能表明能量需求或应激情况（“应激反应假说”），或者相反，在羽毛生长期间的有利条件（“低反应假说”）。在晚成性高山雨燕（Tachymarptis melba）中，我们通过考虑影响 CORT 释放的因素（巢大小、天气）和受高 CORT 水平影响的因素（巢雏大小和状况），来检验哪些因素有助于区分这两种假说。我们在 7 年中测量了 205 只巢雏的 CORTf，并收集了巢大小、体型、身体状况和天气的相关数据。巢雏 CORTf 值与身体状况呈正相关，与恶劣天气呈负相关，支持低反应假说。高山雨燕研究的结果，加上文献综述，表明相对容易收集的巢大小、巢雏大小和状况以及环境因素等参数有助于区分这两种假说。只有在特定物种特征的背景下，对巢雏 CORTf 的有意义解释才是可行的。
