Blood chemistry and health status of Eleonora's falcon (Falco eleonorae) nestlings.

Blood biochemistry offers reliable tools for assessing the physiological condition of wildlife populations, thus aiding their management and conservation. This study provides reference blood biochemistry values for free-living Eleonora's falcon nestlings based on 135 samples collected from 2018 to 2022 in an eastern Crete colony. Significant inter-annual differences in analytes highlight strong environmental effects. Albumin and glucose levels increased with age, whereas phosphorus decreased. Nestlings in better body condition showed higher globulin, calcium, and phosphorus concentrations but lower glucose levels compared to those in poorer condition. Falcons from low-quality nest sites had elevated sodium and uric acid concentrations. No significant differences were detected based on hatching order or sex, except for higher albumin levels in females. Although haemoglobin levels decreased with increasing hatching order and brood size, this trend was not significant, suggesting mild physiological stress in younger fledglings due to intra-brood competition. Relationships between haemoglobin and total protein, calcium, glucose, and uric acid suggest potential biomarkers for monitoring the health of colonies of this species and other raptor populations.