Tarsus length as a simple and robust candidate for early sex determination in partridges across contrasting growing contexts: a case study in Rock partridge (Alectoris graeca Meisner, 1804)

• Three body traits of partridges showed early and marked differences between sexes irrespective of the growth environment. • Quick, cheap, and robust models for sex discrimination of juvenile partridges at 28 and 42 days have been described. • Sex can be established as early as 42 days post hatching by measuring only the tarsus length. Captive breeding of wild Galliform birds for restocking and reintroduction purposes requires efficient management strategies to optimise animal handling, welfare, and release outcomes. Among these, the early definition of sex ratio represents a relevant operational constraint, as sexual dimorphism in some Galliformes generally becomes evident only at advanced developmental stages. This study evaluated the applicability of simple morphometric measurements for early sex discrimination (< 56 days post-hatching) in juveniles of a partridge species ( Alectoris graeca ) reared under contrasting production systems (intensive vs. semi-natural). A total of 33 chicks were included. Body weight and linear body measurements were systematically recorded, and multivariate discriminant analysis was used to identify the most informative traits. Live weight, tarsus length, and head length emerged as the main predictors of sex. The most efficient and easily transferable discriminant model was obtained at 42 days post-hatching using tarsus length as the sole variable, achieving a high canonical correlation (0.89) and 100% classification accuracy under the present experimental conditions, regardless of the rearing system. The proposed approach identifies a practical, rapid, and low-cost candidate for early sexing of juveniles, showing consistent performance across rearing conditions and offering direct applications for breeding management, production planning, and veterinary supervision of captive-reared birds intended for release.