Weathering the storm: The effect of extreme conditions on stress physiology in two songbird species.

Arctic-breeding birds can encounter a wide range of environmental conditions from the time they arrive on their breeding grounds through departure on autumn migration. With climate change, weather conditions are becoming more variable with an increase in the occurrence of early season snowstorms and later snow-free dates in the foothills of the Brooks Range in Alaska, USA. In response to stressful events in the Arctic, birds activate the hypothalamic-pituitary-adrenal (HPA) axis in order to modify physiology and behavior through the actions of corticosterone. The degree to which the HPA axis is activated is thought to be regulated by the interaction of energetic status and environmental conditions. We investigated the impacts of storm-free and stormy environmental conditions on Lapland longspur (Calcarius lapponicus) and white-crowned sparrows (Zonotrichia leucophrys gambelii) stress physiology in the summers of 2011-2015 to understand organism-environment interactions. Over the duration of study, snowstorms occurred three out of the four years which affected the timing of snowmelt and ultimately breeding. In absence of snowstorms, environmental conditions varied greatly across years with 2013 being classified as extreme and as a consequence resulted in elevated HPA axis activity in Lapland longspurs but not White-crowned sparrows. In response to snowstorms during the period of egg-laying, HPA axis activity was increased in Lapland longspurs but reduced in White-crowned sparrows compared to storm-free conditions. Further investigation into HPA axis activity in response to snowstorms in Lapland longspurs indicated that stress profiles were dependent on parental status. During snowstorms, pre-parental birds compared to parental birds had higher stress-induced levels of corticosterone. In conclusion, HPA axis activity is highly plastic and integrates environmental conditions and parental status to help individuals cope with unpredictable events and these responses are species specific.