Under the weather: Corticosterone levels in wild nestlings are associated with ambient temperature and wind

Animals time reproductive events to overlap with periods of favorable environmental conditions. However, weather conditions can be unpredictable. Young animals may be particularly susceptible to extreme weather during sensitive developmental periods. Here, we investigated the effects of adverse weather conditions on corticosterone levels (a hormone linked to the avian stress response) and body condition of wild nestling zebra finches (Taeniopygia guttata). We sought to tease apart the direct versus indirect (i.e. parental) effects of weather on nestling physiology and condition by increasing parental work load with a clutch manipulation experiment. We found that high temperatures were associated with lower levels of restraint-induced corticosterone and high wind speeds were associated with higher levels of baseline corticosterone. We found no associations between weather and nestling body condition. However, clutch manipulation did affect body condition, with nestlings from experimentally enlarged clutches in worse condition compared to nestlings from experimentally reduced clutches. Our findings suggest that weather can directly affect wild nestlings via changes in corticosterone levels. Further research is needed to understand how changes in corticosterone levels affect phenotype and survival in wild nestlings. Understanding how developing animals respond to changes in environmental predictability and extreme weather is vital for understanding the potential for rapid adaptation in the face of changing climatic conditions.