{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,11]],"date-time":"2026-10-11T13:29:30Z","timestamp":1791725370856,"version":"4.3.4"},"reference-count":62,"publisher":"MDPI AG","issue":"7","license":[{"start":{"date-parts":[[2023,3,30]],"date-time":"2023-03-30T00:00:00Z","timestamp":1680134400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Animals"],"abstract":"<jats:p>Biometric analysis allows the sexing of most vertebrates, particularly birds. Birds of prey, and, especially, the Bonelli\u2019s eagle (Aquila fasciata), show reverse sexual dimorphism (i.e., females are usually larger than males). In contrast to blood sampling, the use of morphometrics allows sex determination using a non-invasive method, and, therefore, it facilitates fieldwork. By means of a linear discriminant analysis of biometric variables, we obtained different equations that allow the sexing of nestlings and adult Bonelli\u2019s eagles. We sampled 137 Bonelli\u2019s eagles, 82 nestlings and 55 adults in eastern Spain during the period 2015\u20132022. The sexes obtained after linear discriminant analysis were compared with their molecular sexing. The validation procedure of the linear discriminant equations facilitated the reduction of the number of variables used and, consequently, optimised working time and sexing accuracy. After validation, some equations showed a 100% sexing efficiency for Bonelli\u2019s eagles, particularly for adults. Our results showed that the variables with smaller overlap between the sexes were the lateral tarsus length and dorso-ventral tarsus length, particularly in nestlings. The rest of the variables showed some overlap between the sexes in both age classes. The results we obtained enable the sexing of juvenile and adult Bonelli\u2019s eagles in the field using just these two measurements. Hence, this is an easy, accurate, quick and non-invasive method with multiple applications, including in studies on population dynamics, survival analysis or extinction risk assessments, which, ultimately, could contribute to the improvement of the conservation status of this endangered species.<\/jats:p>","DOI":"10.3390\/ani13071201","type":"journal-article","created":{"date-parts":[[2023,3,30]],"date-time":"2023-03-30T01:05:26Z","timestamp":1680138326000},"page":"1201","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":5,"title":["Non-Invasive Sex Determination of Nestlings and Adult Bonelli\u2019s Eagles Using Morphometrics"],"prefix":"10.3390","volume":"13","author":[{"given":"Irene","family":"Estell\u00e9s-Domingo","sequence":"first","affiliation":[{"name":"Movement Ecology Lab, Cavanilles Institute of Biodiversity and Evolutionary Biology, University of Valencia, C\/Catedr\u00e1tico Jos\u00e9 Beltr\u00e1n 2, E-46980 Paterna, Valencia, Spain"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-5269-652X","authenticated-orcid":false,"given":"Pascual","family":"L\u00f3pez-L\u00f3pez","sequence":"additional","affiliation":[{"name":"Movement Ecology Lab, Cavanilles Institute of Biodiversity and Evolutionary Biology, University of Valencia, C\/Catedr\u00e1tico Jos\u00e9 Beltr\u00e1n 2, E-46980 Paterna, Valencia, Spain"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2023,3,30]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"193","DOI":"10.3161\/000164509X482777","article-title":"Natal dispersal and recruitment of two Bonelli\u2019s Eagles Aquila fasciata: A four-year satellite tracking study","volume":"44","author":"Urios","year":"2009","journal-title":"Acta Ornithol."},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"923","DOI":"10.1007\/s10344-010-0391-z","article-title":"Satellite telemetry reveals individual variation in juvenile Bonelli\u2019s eagle dispersal areas","volume":"56","author":"Urios","year":"2010","journal-title":"Eur. J. Wildl. Res."},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"591","DOI":"10.2307\/4574","article-title":"Age structure and survival in a sparrowhawk population","volume":"52","author":"Newton","year":"1983","journal-title":"J. Anim. Ecol."},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"317","DOI":"10.1111\/j.1474-919X.1986.tb02682.x","article-title":"Sex ratio variation in birds","volume":"128","year":"1986","journal-title":"Ibis"},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"454","DOI":"10.1038\/375454a0","article-title":"Sex of the last wild Spix\u2019s macaw","volume":"375","author":"Griffiths","year":"1995","journal-title":"Nature"},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"336","DOI":"10.1080\/00063651003674953","article-title":"Morphometric sex determination of young Ospreys Pandion haliaetus using discriminant analysis","volume":"57","author":"Muriel","year":"2010","journal-title":"Bird Study"},{"key":"ref_7","first-page":"359","article-title":"Sex identification in the Spanish imperial eagle","volume":"63","author":"Ferrer","year":"1992","journal-title":"J. Field Ornithol."},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"145","DOI":"10.2307\/3544210","article-title":"The evolution of reversed sexual dimorphism in birds of prey","volume":"40","author":"Wheeler","year":"1983","journal-title":"Oikos"},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"283","DOI":"10.2307\/3565349","article-title":"Reversed sexual dimorphism in raptors: Which sex changed size?","volume":"56","author":"Montgomerie","year":"1989","journal-title":"Oikos"},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"532","DOI":"10.1093\/biolinnean\/blz201","article-title":"Why female birds of prey are larger than males","volume":"129","author":"Schoenjahn","year":"2020","journal-title":"Biol. J. Linn. Soc."},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"467","DOI":"10.1007\/s10682-005-0293-9","article-title":"The evolution of reversed sexual size dimorphism in hawks, falcons and owls: A comparative study","volume":"19","year":"2005","journal-title":"Evol. Ecol."},{"key":"ref_12","first-page":"128","article-title":"Methods for gender determination of Crested Caracaras","volume":"33","author":"Morrison","year":"1999","journal-title":"J. Raptor Res."},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"361","DOI":"10.3356\/JRR-11-32.1","article-title":"Morphometrics and sex determination in the endangered Bearded Vulture (Gypaetus barbatus)","volume":"45","author":"Gil","year":"2011","journal-title":"J. Raptor Res."},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"261","DOI":"10.13157\/arla.60.2.2013.261","article-title":"Sex differentiation of Bonelli\u2019s eagle Aquila fasciata in western europe using morphometrics and plumage colour patterns","volume":"60","year":"2013","journal-title":"Ardeola"},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"108","DOI":"10.3356\/JRR-12-28.1","article-title":"Morphometric sex determination of North American Golden Eagles","volume":"47","author":"Harmata","year":"2013","journal-title":"J. Raptor Res."},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"153","DOI":"10.5194\/we-20-153-2020","article-title":"Cohort effect on discriminant rate: The case of greater flamingo (Phoenicopterus roseus) chicks sexed with morphological characters","volume":"20","author":"Boucheker","year":"2020","journal-title":"Web Ecol."},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"1251","DOI":"10.1098\/rspb.1996.0184","article-title":"Sex identification in birds using two CHD genes","volume":"263","author":"Griffiths","year":"1996","journal-title":"Proc. R. Soc. London. Ser. B Biol. Sci."},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"116","DOI":"10.2307\/3677252","article-title":"A simple and universal method for molecular sexing of non-ratite birds","volume":"30","author":"Fridolfsson","year":"1999","journal-title":"J. Avian Biol."},{"key":"ref_19","first-page":"3","article-title":"Molecular techniques for sex identification in birds","volume":"43","author":"Dubiec","year":"2006","journal-title":"Biol. Lett."},{"key":"ref_20","first-page":"20","article-title":"Sex determination in booted eagles (Hieraaetus pennatus) using molecular procedures and discrimiant function analysis","volume":"35","author":"Ferrer","year":"2001","journal-title":"J. Raptor Res."},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"357","DOI":"10.3356\/JRR-11-84.1","article-title":"Sexing Adult and Nestling Red-Shouldered Hawks Using Morphometrics and Molecular Techniques1","volume":"46","author":"Dykstra","year":"2012","journal-title":"J. Raptor Res."},{"key":"ref_22","unstructured":"Cramp, S., Ferguson-Lees, I.J., Gillmor, R., Hollom, P., Hudson, R., Nicholson, E.M., Ogilvie, M., Olney, P., Voous, K., and Wattel, J. (1983). The Birds of the Western Palearctic, Oxford University Press."},{"key":"ref_23","unstructured":"Ferguson-Lees, J., and Christie, D.A. (2001). Raptors of the World, Houghton Mifflin Harcourt."},{"key":"ref_24","first-page":"273","article-title":"Age estimation and growth patterns in nestling Bonelli\u2019s Eagles","volume":"29","author":"Codina","year":"1995","journal-title":"J. Raptor Res."},{"key":"ref_25","first-page":"187","article-title":"Sexing Bonelli\u2019s Eagle nestlings: Morphometrics versus molecular techniques","volume":"35","author":"Palma","year":"2001","journal-title":"J. Raptor Res."},{"key":"ref_26","doi-asserted-by":"crossref","first-page":"3","DOI":"10.1177\/17581559211063123","article-title":"Towards accurate and simple morphometric sex differentiation in Bonelli\u2019s Eagle Aquila fasciata nestlings: Interpopulation variations and influence of growth conditions","volume":"15","author":"Bautista","year":"2022","journal-title":"Avian Biol. Res."},{"key":"ref_27","doi-asserted-by":"crossref","unstructured":"Del Moral, J.C., and Molina, B. (2018). El \u00e1guila Perdicera en Espa\u00f1a, Poblaci\u00f3n Reproductora en 2018 y M\u00e9todo de Censo, SEO\/BirdLife.","DOI":"10.31170\/0065"},{"key":"ref_28","doi-asserted-by":"crossref","first-page":"57","DOI":"10.1093\/cz\/zoab010","article-title":"Tri-axial accelerometry shows differences in energy expenditure and parental effort throughout the breeding season in long-lived raptors","volume":"68","author":"Perona","year":"2022","journal-title":"Curr. Zool."},{"key":"ref_29","doi-asserted-by":"crossref","unstructured":"Moroll\u00f3n, S., Urios, V., and L\u00f3pez-L\u00f3pez, P. (2022). Home-Range Size and Space Use of Territorial Bonelli\u2019s Eagles (Aquila fasciata) Tracked by High-Resolution GPS\/GSM Telemetry. Diversity, 14.","DOI":"10.20944\/preprints202210.0159.v2"},{"key":"ref_30","doi-asserted-by":"crossref","first-page":"849","DOI":"10.1007\/s10336-022-01982-5","article-title":"Fifteen days are enough to estimate home-range size in some long-lived resident eagles","volume":"163","author":"Urios","year":"2022","journal-title":"J. Ornithol."},{"key":"ref_31","doi-asserted-by":"crossref","first-page":"59","DOI":"10.1016\/j.biocon.2019.01.010","article-title":"Holidays? Not for all. Eagles have larger home ranges on holidays as a consequence of human disturbance","volume":"231","author":"Perona","year":"2019","journal-title":"Biol. Conserv."},{"key":"ref_32","doi-asserted-by":"crossref","first-page":"335","DOI":"10.1080\/00063650709461493","article-title":"Population size, breeding performance and territory quality of Bonelli\u2019s eagle Hieraaetus fasciatus in eastern Spain","volume":"54","author":"Urios","year":"2007","journal-title":"Bird Study"},{"key":"ref_33","first-page":"1","article-title":"Efecto de la altitud y de la disponibilidad de presas en la fecha de puesta del \u00e1guila-azor perdicera (Hieraaetus fasciatus) en la provincia de Granada (SE de Espa\u00f1a)","volume":"47","year":"2000","journal-title":"Ardeola"},{"key":"ref_34","doi-asserted-by":"crossref","first-page":"21969","DOI":"10.1038\/s41598-022-26153-7","article-title":"Potential negative effects of the installation of video surveillance cameras in raptors\u2019 nests","volume":"12","year":"2022","journal-title":"Sci. Rep."},{"key":"ref_35","doi-asserted-by":"crossref","first-page":"201","DOI":"10.1080\/03079450902912135","article-title":"Prevalence and genotyping of Trichomonas gallinae in pigeons and birds of prey","volume":"38","year":"2009","journal-title":"Avian Pathol."},{"key":"ref_36","doi-asserted-by":"crossref","first-page":"339","DOI":"10.2108\/zsj.20.339","article-title":"Sex identification by alternative polymerase chain reaction methods in Falconiformes","volume":"20","author":"Ito","year":"2003","journal-title":"Zool. Sci."},{"key":"ref_37","unstructured":"Zar, J. (2014). Biostatistical Analysis, Pearson. [5th ed.]."},{"key":"ref_38","unstructured":"Kassambara, A. (2023, March 28). Rstatix: Pipe-Friendly Framework for Basic Statistical Tests. 2023. Version 0.7.2. Available online: https:\/\/CRAN.R-project.org\/package=rstatix."},{"key":"ref_39","unstructured":"Dillon, W.R., and Goldstein, M. (1984). Multivariate Analysis: Methods and Applications, Wiley."},{"key":"ref_40","doi-asserted-by":"crossref","first-page":"78","DOI":"10.1525\/auk.2011.10129","article-title":"Sexing birds using discriminant function analysis: A critical appraisal","volume":"128","author":"Monceau","year":"2011","journal-title":"Auk"},{"key":"ref_41","unstructured":"McLachlan, G.J. (2005). Discriminant Analysis and Statistical Pattern Recognition, John Wiley & Sons."},{"key":"ref_42","unstructured":"R Core Team (2023, March 28). R: A Language and Environment for Statistical Computing 2022. Available online: http:\/\/www.r-project.org\/index.html."},{"key":"ref_43","unstructured":"Wickham, H., Fran\u00e7ois, R., Henry, L., M\u00fcller, K., and Vaughan, D. (2023, March 28). Posit PBC Dplyr: A Grammar of Data Manipulation 2023. Version 1.1.1. Available online: https:\/\/CRAN.R-project.org\/package=dplyr."},{"key":"ref_44","unstructured":"Kuhnaut, M., Wing, J., Weston, S., Williams, A., Keefer, C., Engelhardt, A., Cooper, T., Mayer, Z., Kenkel, B., and R Core Team (2022). Caret: Classification and Regression Training 2022, R Core Team."},{"key":"ref_45","unstructured":"Makowskiaut, D., Najberg, H., Simko, V., and Epskamp, S. (2023, March 28). psycho: Efficient and Publishing-Oriented Workflow for Psychological Science 2021. Version 0.6.1. Available online: https:\/\/CRAN.R-project.org\/package=psycho."},{"key":"ref_46","unstructured":"M\u00fcller, K., Wickham, H., Francois, R., and Bryan, J. (2023, March 28). Tibble: Simple Data Frames 2022. Version 3.2.1. Available online: https:\/\/CRAN.R-project.org\/package=tibble."},{"key":"ref_47","unstructured":"Wei, T., Simko, V., Levy, M., Xie, Y., Jin, Y., Zemla, J., Freidank, M., Cai, J., and Protivinsky, T. (2023, March 28). Corrplot: Visualization of a Correlation Matrix 2021. Version 0.92. Available online: https:\/\/CRAN.R-project.org\/package=corrplot."},{"key":"ref_48","doi-asserted-by":"crossref","first-page":"539","DOI":"10.3356\/JRR-20-115","article-title":"Morphometric Sex Identification of Nestling and Free-Flying Tasmanian Wedge-Tailed Eagles (Aquila audax fleayi)","volume":"55","author":"Pay","year":"2021","journal-title":"J. Raptor Res."},{"key":"ref_49","first-page":"524","article-title":"Physical development of nestling bald eagles with emphasis on the timing of growth events","volume":"96","author":"Bortolotti","year":"1984","journal-title":"Wilson Bull."},{"key":"ref_50","doi-asserted-by":"crossref","first-page":"74","DOI":"10.1111\/j.1557-9263.2006.00003.x","article-title":"Sex determination of Red-tailed Hawks (Buteo jamaicensis calurus) using DNA analysis and morphometrics","volume":"77","author":"Donohue","year":"2006","journal-title":"J. Field Ornithol."},{"key":"ref_51","doi-asserted-by":"crossref","first-page":"495","DOI":"10.1086\/284498","article-title":"Influence of sibling competition on nestling sex ratios of sexually dimorphic birds","volume":"127","author":"Bortolotti","year":"1986","journal-title":"Am. Nat."},{"key":"ref_52","doi-asserted-by":"crossref","first-page":"195","DOI":"10.2989\/00306525.2016.1259185","article-title":"Gender-related morphometric differences in mature and nestling Crowned Eagles, with comments on ringing of eagle nestlings in KwaZulu-Natal, South Africa","volume":"88","author":"McPherson","year":"2017","journal-title":"Ostrich"},{"key":"ref_53","first-page":"45","article-title":"Determining age and sex of nestling Gyrfalcons","volume":"23","author":"Poole","year":"1989","journal-title":"J. Raptor Res."},{"key":"ref_54","doi-asserted-by":"crossref","first-page":"387","DOI":"10.5962\/p.356993","article-title":"Growth of nestling Merlins, Falco columbarius","volume":"106","author":"Sodhi","year":"1992","journal-title":"Can. Field-Nat. Ott. ON"},{"key":"ref_55","doi-asserted-by":"crossref","first-page":"385","DOI":"10.3356\/JRR-13-00007.1","article-title":"Morphometrics and sexual dimorphism of Chinese Goshawks (Accipiter soloensis)","volume":"47","author":"Choi","year":"2013","journal-title":"J. Raptor Res."},{"key":"ref_56","doi-asserted-by":"crossref","first-page":"301","DOI":"10.3356\/JRR-15-60.1","article-title":"Morphometric sex determination of after-hatch-year Bald Eagles in Louisiana","volume":"50","author":"Smith","year":"2016","journal-title":"J. Raptor Res."},{"key":"ref_57","doi-asserted-by":"crossref","first-page":"363","DOI":"10.1111\/j.1474-919X.1993.tb02107.x","article-title":"A comparison of digestive efficiency in birds of prey","volume":"135","author":"Barton","year":"1993","journal-title":"Ibis"},{"key":"ref_58","doi-asserted-by":"crossref","first-page":"412","DOI":"10.3356\/JRR-21-43","article-title":"Broad-Winged Hawk Size Varies by Sex and Latitude in North America","volume":"56","author":"Bordner","year":"2022","journal-title":"J. Raptor Res."},{"key":"ref_59","doi-asserted-by":"crossref","first-page":"1013","DOI":"10.1016\/j.biocon.2008.01.011","article-title":"Incorporating spatial structure and stochasticity in endangered Bonelli\u2019s eagle\u2019s population models: Implications for conservation and management","volume":"141","author":"Soutullo","year":"2008","journal-title":"Biol. Conserv."},{"key":"ref_60","doi-asserted-by":"crossref","first-page":"239","DOI":"10.1890\/12-1248.1","article-title":"From local monitoring to a broad-scale viability assessment: A case study for the Bonelli\u2019s Eagle in western Europe","volume":"83","author":"Real","year":"2013","journal-title":"Ecol. Monogr."},{"key":"ref_61","first-page":"9","article-title":"Dispersal of juvenile and immature Bonelli\u2019s Eagles in northeastern Spain","volume":"35","author":"Real","year":"2001","journal-title":"J. Raptor Res."},{"key":"ref_62","doi-asserted-by":"crossref","first-page":"173","DOI":"10.1525\/auk.2009.09143","article-title":"Determinants of territorial recruitment in Bonelli\u2019s eagle (Aquila fasciata) populations","volume":"127","author":"Real","year":"2010","journal-title":"Auk"}],"container-title":["Animals"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/2076-2615\/13\/7\/1201\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,10]],"date-time":"2025-10-10T19:06:44Z","timestamp":1760123204000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/2076-2615\/13\/7\/1201"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2023,3,30]]},"references-count":62,"journal-issue":{"issue":"7","published-online":{"date-parts":[[2023,4]]}},"alternative-id":["ani13071201"],"URL":"https:\/\/doi.org\/10.3390\/ani13071201","relation":{},"ISSN":["2076-2615"],"issn-type":[{"value":"2076-2615","type":"electronic"}],"subject":[],"published":{"date-parts":[[2023,3,30]]}}}