RT Journal Article T1 Haematological and biochemical reference values for Bonelli's eagles in the wild and in captivity: implications for conservation and rehabilitation programs A1 González González, Fernando A1 Perez Luzardo, Octavio A1 Revuelta Rueda, Luis A1 Suárez Regalado, Laura A1 Moraleda Fernández, Virginia A1 Carrero Ruíz, Alicia A1 Del Río, Laura AB Background Haematological and clinical biochemistry analyses are essential tools for evaluating the health status of avian species, including the endangered Bonelli’s eagle. Despite their importance, existing reference intervals (RIs) for such parameters in raptor species are frequently constrained by limited sample sizes, thus complicating clini cal interpretations. This research followed the American Society for Veterinary Clinical Pathology (ASVCP) guidelines to establish haematological and clinical biochemistry reference intervals for the Bonelli’s eagle, utilizing an indirect approach. Conservation initiatives of the Bonelli’s eagle have provided a unique opportunity to gather a high number of samples under various conditions, facilitating a comprehensive comparison between wild and captive populations. Over the course of six years, from 2016 to 2021, our research analyzed 516 blood samples collected within the frame work of a European Life Project. After rigorous data cleaning and stringent selection criteria application, a representa tive sample of 184 birds was determined. Various physiological parameters and blood lead levels were quantifed in healthy individuals. Additionally, we used Principal Component Analysis to discern distinctions between popula tions and to investigate potential interrelationships among the diverse parameters. Results We established Reference Intervals for three distinct reference groups of birds: wild nestlings (n = 72), cap tive nestlings (n = 45), and adults (n = 49). Our fndings indicate that age signifcantly afects many blood param eters. Meanwhile, gender impacts only a few parameters in adult birds. Notably, wild nestlings exhibited higher levels of AST, K, TP, and Pb in their blood compared to those bred in captivity. Conclusions This paper provides the frst reliable RI for physiological, haematological, and clinical biochemistry parameters in both nestling and adult Bonelli’s eagles. The data will augment the knowledge of the physiology of this endangered raptor, contributing signifcantly to the understanding and monitoring of both free-living birds and cap tivity programs PB BioMed Central YR 2025 FD 2025 LK https://hdl.handle.net/20.500.14352/120573 UL https://hdl.handle.net/20.500.14352/120573 LA eng NO González, F., Perez-Luzardo, O., Revuelta, L., Suárez-Regalado, L., Moraleda-Fernández, V., Carrero-Ruíz, A., & Del Río, L. (2025). Haematological and biochemical reference values for Bonelli's eagles in the wild and in captivity: implications for conservation and rehabilitation programs. BMC veterinary research, 21(1), 342. https://doi.org/10.1186/s12917-025-04790-0 NO Authors’ contributions Conception of the work FG, LR; design of the study FG and LDR; blood sampling and laboratory analysis LS, VM, AC, OPL; data analysis LDR; writing— original draft preparation, FG, LR, OPL, LDR; writing—review and editing, FG, LR, OPL, LDR. All authors have read and agreed to the published version of the manuscript. NO European Commission NO Ministerio para la Transición Ecológica y Reto Demográfco ( España) DS Docta Complutense RD 13 oct 2025