Precocial bird mothers shape sex differences in the behavior of their chicks.

Compared to mammals and altricial birds, evaluations of differences related to precocial birds' sex have often been limited to sexual behavior. Nevertheless, the extensive use of precocial bird models for investigating behavioral development issues requires in depth knowledge concerning the emergence of sex differences. Here, we evaluated behavioral differences between Japanese quail chicks in relation to their sex. We know that maternal influences are strong and early social environment shapes behavioral development in this species. Therefore, we investigated the emergence of sex differences in two very different early social situations to evaluate the impact of precocial bird mothers on sex differences. We assessed behavioral differences related to sex of (1) non-brooded chicks and of (2) brooded chicks, using various ethological tests to evaluate emotional reactivity and social motivation differences related to sex. Our results show that both non-brooded and brooded chicks present behavioral differences related to sex. They differed greatly according to chicks' early experience. Sex-related differences between maternally deprived (non-brooded) chicks concerned mainly fearfulness, whereas differences between male and female brooded chicks concerned mainly their reactions to social isolation. We hypothesize that mothers attenuate sex differences related to fearfulness by being a model for responses to fear-eliciting situations and by providing a similar secure basis to both males and females. We finally propose that mothers induce differences in chicks' sociality by providing asymmetrical care toward males and females.