© Yves Bötsch
How do hoopoes respond to stress during breeding? Does stress during this period affect reproductive success and survival? These questions were investigated in a population of hoopoes in the Swiss Rhone valley.
More and more studies show that responses of birds to stress depend on the circumstances. Which factors determine, how a bird responds to stress? Does a stress response influence fitness?
In two master theses in two subsequent years we investigated whether the relative value of a brood influenced the strength of the physiological stress response and whether there is a correlation between plasma corticosterone of adult hoopoes during the nestling period and the breeding success (short term effects) and/or survival (long-term effects).
The baseline level of corticosterone as well as the adrenocortical response to handling stress varied with body condition and sex and depended on whether parents made a first or a second brood attempt. Plasma corticosterone correlated negatively with body condition. In addition, parents responded less to stress if they wanted to raise their brood by all means in the face of little chances to raise yet another brood in their life. The stress response in females, which have a higher brood investment, was smaller than in males. These results suggest, that females, which are indispensable for the brood, react less to stress to be able to finish the brood successfully. The results of the second year showed that females which had lower corticosterone levels the previous year had a higher probability to return the following year in contrast to females with an increased corticosterone level. We also analysed prolactin, a hormone mediating parental care. In the brooding phase, we found higher baseline levels in females than their mates which feed them and the chicks during this stage. Stress induced a decrease in prolactin levels, which was less pronounced in females during the very early stage of brooding compared to females in later stages.