Adaptive changes of glucocorticoids in work load gradients
Individuals vary significantly in how they respond to energetic challenges. Generally, baseline glucocorticoid levels increase in response to an increased work-load, but individuals differ in the degree of this response. One explanation is that trade-offs between immediate survival and fitness are resolved differently in accordance with an individual’s physiological condition, such as oxidative stress level and nutritional state. On the other hand, it is also possible that no trade-offs are involved and that glucocorticoids promote both survival and fitness. I am testing these hypotheses with experiments in captivity and in the wild. To see how these workload challenges play out in “real life”, I study adult great tits during the breeding season in a forest close to the Max Planck Institute for Ornithology in Bavaria. For my captive study I am using starlings trained to fly in a wind tunnel in collaboration with Scott McWilliams and Ulf Bauchinger.