On again, off again: acute stress response and negative feedback together predict resilience to experimental challenges

1. Individuals often vary markedly in their ability to cope with stressors, but the drivers of this variation remain poorly understood. Many studies have tested relationships among individual variation in glucocorticoid levels and the response to challenges – often finding inconsistent patterns; however, few have addressed whether variation in the capacity to terminate the stress response through negative feedback is associated with stress resilience.
2. While conceptual models predict that interactions among different components of hypothalamic-pituitary-adrenal (HPA) axis regulation may be important predictors of the phenotypic and fitness effects of stress, we are aware of no previous experimental tests of this hypothesis.
3. We investigate whether individual variation in HPA axis regulation is related to resilience to experimental challenges in free-living tree swallows (Tachycineta bicolor). We mimicked salient natural challenges by temporarily reducing flight efficiency or incre...