Ontogeny of Diet and Behavior of a Wild, Critically Endangered Lemur ( <i>Indri indri</i> )

The early developmental period plays a key role in primate behavioral outcomes. Understanding the behavioral ecology of infant indris (Indri indri) helps to identify resources needed during early developmental stages, the weaning process, and the role of mothers in developing infants' survival abilities. In this study, we investigated the behavioral and dietary development of wild Indri indri in Madagascar. We found that infants undergo significant behavioral transitions during their early growth, which reflect their maturation and adaptation to the environment. Play is critical in developing locomotion skills and acquiring knowledge about dietary preferences. Social interactions, initially centered on grooming with the mother, began to extend to other group members as early as 4 months of age, reflecting a shift from maternal care to broader social bonding. Additionally, territorial behaviors such as scent marking became more prominent in later month age classes when new behaviors, such as singing, emerged. We observed a co-feeding relationship between young indris and their mothers that ceased around 1 year of age. Lauraceae was the most-eaten plant family in the first 2 years of life, and we observed shifts in plant taxa and plant parts consumption with age. Milk consumption was not observed after 7 months of age. We also highlighted the presence of coprophagy and geophagy in indri infants, which were observed on several occasions consuming maternal feces and soil. These behaviors could play a role in maternal microbiota inoculation and toxin regulation, though further evidence is needed, even at a young age. Our work highlighted the dietary requirements and behavioral development of indri infants. These Critically Endangered lemurs have never been bred in captivity; our findings provide foundational data to inform future studies and potential conservation strategies.