Young chicks quickly lose their spontaneous preference to aggregate with females

It is not clear when and how animals start to discriminate between male and female conspecifics and how this distinction drives their social behaviour. A study on pheasants found that 1-week-old chicks (Phasianus colchicus) preferentially aggregated with same-sex peers and this trend became more pronounced through development, suggesting that sexual segregation increases during ontogeny. However, it remains unclear whether this ability depends on experience or develops spontaneously. Using a similar experimental protocol, we investigated whether sex discrimination is present at birth in domestic chickens (Gallus gallus) by testing the social preferences of young chicks with clutch mates. We measured the amount of time spent close to male and female conspecifics in visually inexperienced chicks. Soon after hatching, both males and females preferentially aggregated with females. To clarify whether the experience with conspecifics modifies the initial preference for females, we used an imprinting procedure. We exposed chicks to conspecifics of the same sex, different sex or both sexes for 3 days and then tested their preferences to aggregate with males or females. No sex preference was observed after 3 days of imprinting exposure. The disappearance of the initial sex preference shows that, although chicks can discriminate between conspecifics of different sex, sex segregation does not influence sex preferences in the first week of life. We suggest that the absence of sexual assortment in the first week of age can enhance the social cohesion of the flock. SIGNIFICANT STATEMENT: The ability to discriminate males from females affects a wide range of social behaviours, including the preferences for own sex conspecifics during sex segregation and the choice of a partner in the mating period. However, it remains unclear when and how males and females start to discriminate members of the same/different sex. We tested the domestic chicks to explore whether sex discrimination is present at birth or appears later on. Males and females discriminated between sexes at hatching and preferred to spend more time with female chicks. However, this preference disappeared after exposure to same-sex, different-sex or mixed-sex chicks. The lack of a preference for a specific sex may increase group cohesion postponing the appearance of sex segregation later in life, when chicks move further from their group.