Human pressure may pose a threat to Mediterranean Golden Eagle's (Aquila chrysaetos homeyeri) nestlings' welfare

Mediterranean Golden Eagles (Aquila chrysaetos homeyeri) are crucial for maintaining the balance of the ecosystem they live in. Human presence and some human activities are recognized as major disturbance factors affecting their welfare. In the present study, we evaluated through the measurement of feather corticosterone (CORTf), the welfare state of nestlings subjected to different levels of human pressure. Nestlings were sampled in different locations in Spain and Portugal for two consecutive years (2018, 2019). CORTf levels were higher in groups of individuals living in most populated areas and positively correlated with the proximity to airports, suggesting that human presence and noise pollution generated by aircraft may be a source of stress for developing eaglets, affecting their physiological state. CORTf levels were also related to mortality, finding low mean levels in individuals dying in the short-run. Finally, the relation between CORTf and other commonly used stress indicators such as the intensity of the color of the hue of cere and the number of fault bars in the tail of the nestlings was investigated. Considering the hue of cere, a significant negative strong correlation with the corticosterone levels in nestlings was found in samples from 2018 suggesting that nestlings in poorer nutritional conditions may present higher stress levels, whereas no correlation with the number of fault bars was found.