Energetic Priorities Across the Stages of Development: Effects of Age, Sex, and Seasonal Reproduction on Activity Budgets in Verreaux's sifaka (Propithecus verreauxi)

Abstract

The immature period is an essential time of physical and behavioral development in which individuals prepare to navigate their environment as adults. Activity budgets provide valuable insight into the tradeoffs individuals make based on their energetic priorities. We hypothesized that energetic priorities differ across the stages of development based on the distinct social and ecological needs of that stage. We analyzed 31,113.5 h of focal instantaneous sampling data from 2007 to 2024 on 73 Verreaux's sifaka (Propithecus verreauxi) living in Kirindy Mitea National Park, Madagascar to investigate the effects of age class, sex, and seasonality on activity budgets. Juveniles and subadults devoted significantly more time to social activity than adults. Subadults fed less than other age classes, and we detected no differences in resting among age classes. Among all age classes, males devoted more time to social activity than females, and all age classes displayed sex differences in additional activities. All age-sex classes exhibited similar seasonal patterns in activity budgets. Our results indicate that social activity may be especially important in the developmental period to gain experience and establish social relationships before adulthood. Sex differences in social activity appear to emerge earlier than adulthood as a predisposition for the reproductive roles of adulthood. Overall, we found that energetic priorities differ between stages of development, and evidence is mixed regarding whether these differences are primarily due to the onset of reproduction.