Biometry and sex discrimination of first calendar year Cetti’s Warbler (<i>Cettia cetti</i>) by discriminant analysis

A method is proposed here for distinguishing the sexes of Cetti’s warblers in their first calendar year (Euring age code=3) based on the use of discriminant analysis. In the initial phase of the study, 118 subjects of known sex (62 males and 56 females), captured and marked in the Palude Brusà, were subjected to analysis as a calibration sample. The analysis yielded a discriminant function based on the two most significant variables (third primary length, tarsus length), enabling the sexes to be classified with a 99.2%. The function was subsequently tested on the validation sample (n=106), composed of 54 males and 52 females of known sex ringed in Punte Alberete (north-eastern Italy) and the Trasimeno Emissary (central Italy), obtaining an accuracy classification equal to 99.1%. A global discriminant analysis was subsequently conducted, integrating the data from the three locations into a unified sample (n=224). This analysis yielded a function that accurately classified 99.1% of the females and 100% of the males. The resulting equation represents a rapid and precise method for distinguishing the sexes of first-calendar year Cetti’s warblers. Additionally, it can assist in the appropriate selection of ring size, which differs between the sexes.