An early-life challenge: becoming an older sibling in wild mandrills

In monotocous mammals, most individuals experience the birth of a younger
sibling. This period may induce losses in maternal care and can be
physiologically, energetically and emotionally challenging for the older
sibling, yet has rarely been studied in wild primates. We used behavioural
data collected from a natural population of mandrills to investigate
changes in maternal care and mother-juvenile relationship throughout the
transition to siblinghood (TTS), by comparing juveniles who recently
experienced the birth of a younger sibling, to juveniles who did not. We
found that the TTS was associated with an abrupt cessation of the weaning
process for the juvenile, and to a decrease in maternal affiliation.
Juveniles’ reactions were sex-specific, as males associated less with
their mother, while females tended to groom their mother more often after
the birth of their sibling. Despite the substantial loss of maternal care
juveniles did not show an increase in conflict or anxiety-related
behaviours. This study contributes to explain why short interbirth
intervals often pose a risk to juveniles’ survival in monotocous primates.
Our results contrast existing studies and further highlights the
importance of examining the TTS in species and populations with various
life histories and ecologies.