Short-term Dehydration Influences Baseline, but Not Stress-Induced Corticosterone Levels in the House Sparrow (passer Domesticus)

Future environmental variations linked to climate change are expected to influence precipitation regimes, and thus drinking water availability. Dehydration can be a particularly challenging physiological state for most organisms, yet no study has examined the effect of dehydration on the functioning of the Hypothalamus-Pituitary-Adrenal axis in wild endothermic animals, despite its central role in maintaining homeostasis. In this study, we experimentally imposed a temporary water shortage (∼20 hours) to captive House sparrows in order to investigate the consequences of short-term dehydration on baseline and stress-induced corticosterone levels. As expected, water-deprived birds displayed higher plasma osmolality and haematocrit. Additionally, water-deprived birds had lower defecation rates, suggesting that the mechanisms allowing cecal water absorption may be triggered very rapidly during water-deprivation. Baseline, but not stress-induced corticosterone levels were higher in water-deprived birds. Taken together, these results suggest that water-restriction may have critical consequences on several corticosterone-related traits such as energy budget (protein catabolism and possibly feeding reduction), enhanced mobility (to promote water acquisition) and potential responses to predators (thirst threshold overriding the acute stress response). Owing to the possible fitness consequences of such components of the day-to-day life of birds, future studies should aim at investigating the influence of future changes in precipitation regimes and drinking water availability on bird populations.