# Age‐Trajectory of Mother–Infant Relationships in Wild Assamese Macaques

## TL;DR

The study tracks how mother-infant relationships change over time in wild Assamese macaques, showing a sharp decline in maternal care between 1 and 3 months.

## Contribution

The study provides a quantitative baseline for how ecological pressures shape mother-infant behavioral transitions in wild primates.

## Key findings

- Maternal care declines sharply between 1 and 3 months of infant age.
- Infants achieve near-complete independence by the second half of infancy.
- No sex differences were found in mother-infant relationship trajectories.

## Abstract

Maternal care is ubiquitous in mammals, yet its degree and duration vary across taxa. In primates, mothers provide extended care for young and follow similar developmental transitions in the mother–infant relationship, yet at different paces of change. Since ecological pressures shape life‐history traits including female reproductive rate and timing of infant independence, research is needed on mother–infant relationships in wild populations exposed to energetic constraints and predation risk. Assamese macaques (Macaca assamensis) of the study population are seasonal breeders living in an unpredictable environment, where fluctuating food availability imposes energetic challenges on mothers and infants. We quantitatively describe how maternal care and offspring independence develop throughout infancy. Using continuous focal observations on 59 infants, we model the nonlinear age‐trajectories of mother–infant proximity and transitions from dependent to independent feeding and locomotion, and estimated sex differences in these trajectories. Newborns were fully dependent on their mothers for feeding and transport, with mothers maintaining close proximity. A transitional phase emerged between 1 and 3 months of age, marked by reduced maternal proximity and increasing infant independence. During the second half of infancy, infants achieved near‐complete locomotor and feeding independence, while residual proximity and body contact persisted. No sex differences were detected in the mother–infant relationship trajectory. Collectively, the timing of maternal investment aligns with the breeding strategy of this seasonal species, with females balancing investment in current and future reproduction. This study establishes a baseline for examining how ecological variability affects the timing and pace of mother–infant behavioral transitions.

Maternal care in wild Assamese macaques declined sharply between 1 and 3 months of infant age as infant independence increased, and stabilized from around 6 months, with no sex differences in the trajectory. This early shift aligns with the species' seasonal breeding strategy, with females balancing investment in current and future offspring.

Maternal care was initially intense, dropped sharply between 1 and 3 months of infant age, and stabilized at a lower level during the second half of infancy.Infant sex did not influence the mother–infant relationship.Early onset of infant independence was associated with female reproductive strategies that reallocate investment from current offspring toward future reproduction.

Maternal care was initially intense, dropped sharply between 1 and 3 months of infant age, and stabilized at a lower level during the second half of infancy.

Infant sex did not influence the mother–infant relationship.

Early onset of infant independence was associated with female reproductive strategies that reallocate investment from current offspring toward future reproduction.