Differences in social preference between the sexes during ontogeny drive segregation in a precocial species (dataset)

Abstract

Hypotheses for why animals sexually segregate typically rely on adult traits such as differences in sexual roles leading to differences in habitat preferences, or size dimorphism resulting in differences in forage selection or activity budgets. However, segregation can occur in juveniles before such roles or size dimorphism is well established. In humans, leading hypotheses suggest that: 1) sexes differ in their behavioural repertoire and the synchronisation of this behaviour causes segregation; and 2) sexes separate in order to learn and maximise future reproductive roles. We reared pheasants Phasianus colchicus from hatching, for eight weeks, in the absence of adults and predators in a controlled environment with standardised habitat and food provision.

Females aggregated with their own sex from hatching whereas males initially exhibited random association but segregation became pronounced with age. The increase in segregation corresponded to an increase in sexual size dimorphism. By standardising habitat availability, diet and removing predation risk we could reject the Predation Risk Hypothesis and the Forage Selection Hypothesis operating at this age. Activity budgets did not differ between the sexes providing no support for the Behavioural Synchrony or the Activity Budget Hypotheses. Both sexes preferentially approached groups of unfamiliar, same-sex birds in binary choice tests, providing support for the Social Preference Hypothesis. Females may segregate to avoid male aggression, whereas males may segregate to seek opportunities to assert dominance or practice sexual contests.

Sexual segregation therefore appears to become established early in development, especially in precocial species. As such, a clear understanding of ontogenetic factors is essential to further our understanding of adult assortment patterns. This may not be inherent but rather emerge as a consequence of social interactions early in life.