Life history theory predicts that physiological and behavioral responsiveness to stress should be delayed in development until the benefits of heightened reactivity outweigh the costs of potentially chronic glucocorticoid levels. Birds often acquire stress‐responsiveness at locomotor independence, however, both stress‐responsiveness and locomotor ability are delayed in birds with altricial developmental strategies. Parrots (Psittacidae) are extremely altricial, but it is not known whether they also postpone physiological responsiveness to stress until locomotor independence. We quantified individual variation in baseline and stress‐induced plasma corticosterone (CORT) concentrations, the main avian glucocorticoid, in wild green‐rumped parrotlets (Forpus passerinus) of Venezuela at four stages of nestling development. Parrotlet neonates are very underdeveloped and compete for parental care among extreme sibling size hierarchies, a competitive scenario that might benefit from early hypothalamic–pituitary–adrenal (HPA) functionality. Nestlings that underwent a standardized restraint stress‐treatment showed higher average CORT concentrations compared to baseline in all age groups sampled, and exhibited no evidence of age‐related changes in the stress response. This is 2 weeks before locomotor independence and earlier than previously documented for altricial species. Results suggest that precocity of HPA function may be advantageous to growth and survivorship in extremely altricial birds.

中文翻译：

---

极度鸟类鸟类的肾上腺皮质反应的个体发育。

生命史理论预测，应推迟对压力的生理和行为反应，直至增强反应性的益处超过潜在的慢性糖皮质激素水平的代价。鸟类经常在运动独立时获得应激反应，但是，在具有发育性策略的鸟类中，应激反应和运动能力都被延迟。鹦鹉（Psittacidae）具有极强的刺激性，但尚不知道它们是否也将对压力的生理反应推迟到运动独立之前。我们量化了野生绿色腰果鹦鹉（Forpus passerinus）的基线和应激诱导的血浆皮质激素（CORT）浓度（主要的禽类糖皮质激素）的个体差异委内瑞拉）处于雏鸟发育的四个阶段。鹦鹉的新生儿非常不发达，在极度兄弟姐妹的等级体系中竞争父母的照料，这种竞争情况可能得益于早期下丘脑-垂体-肾上腺（HPA）功能。接受标准化约束应激处理的雏鸟在所有采样年龄组中均显示出比基线更高的平均CORT浓度，并且没有显示出与年龄相关的应激反应变化的证据。这是在运动独立之前的2周，并且比以前记载的其他物种早。结果表明，早熟HPA功能可能对极度鸟类的鸟类的生长和存活有利。