According to a 15-year tracking study by wild Sumatra orangutans, not all orangutan mothers are the same. The study, published on Tuesday in the Proceedings of the Royal Society B, demonstrates the forefront of the ongoing differences in parenting methods among individual orangutan mothers, even with different offspring.
Researchers from the Max Planck Institute for Animal Behavior analyzed over 6,000 hours of observations covering 22 pairs of mothers at the Suaq Balimbing study site in Indonesia. They found obvious, individual differences in maternal behaviors that persist in different infants and various environmental conditions.
“Our study shows that Sumatra orangutan mothers are not the same in parenting behavior,” said Revathe Thillaikumar, lead author and postdoctoral researcher of the study. “For example, we found that during developmental periods, some mothers always carry more babies than others, while some mothers terminate physical contact more frequently than others.”
The research team focused on six key maternal behaviors: initiating physical contact, terminating physical contact, initiating close proximity, ending closeness, carrying and feeding nearby babies. These behaviors greatly influence babies to learn key survival skills and drive rainforest canopy.
Beyond the environment
Making the findings particularly important is that these differences remain consistent even considering the many variables known to influence parenting behavior, such as infant age, gender, availability of food, and social status.
“What is particularly interesting is that these differences are consistent among different babies in mothers, even though we consider factors known to affect maternal behavior,” Thillaikumar noted.
Sumatra orangutans have the longest infant dependence period, and the mother provides 6-9 years of care. This extended dependence makes them an ideal species for studying maternal behavior changes.
The researchers found that mothers not only differ in baseline parenting behavior, but also adjust the way they parent as the baby matures.
“We found that mothers made flexible adjustments to parenting behaviors and consistently different from each other in how they made these adjustments,” Thillaikumar explained. “For example, although all mothers tend to terminate spatial proximity more frequently as the baby gets older, some mothers always do more than other mothers in all other offspring.”
The motherhood of non-human primates
The team believes that these consistent differences may indicate individual personality in orangutans – an increasing amount of evidence suggests personality traits transcend humans to other species.
Caroline Schuppli, a team leader at the Max Planck Institute and senior author of the study, highlighted the importance of their findings: “The consistent differences between mothers – in the scope of their behaviors and how these behaviors change within the scope of these behaviors and in the development of infants – orangutans may have an individual mother’s challenge.”
The statistical methods used in this study are particularly rigorous, which considers various factors that may explain behavioral differences. The researchers carefully isolated the real individual differences from other variables, ensuring that their conclusions about maternal behavior patterns are justified.
Interestingly, mothers who exhibited higher than average carrying behaviors showed significantly smaller feeds that were closely similar to offspring. This suggests that larger early-stage investments may lead to faster feeding skills acquisition, thereby reducing the need for close-range feeds developed later.
Future research directions
The discovery opens new avenues to understand how maternal behavior affects long-term developmental outcomes in offspring. However, answering these questions will take years of observation.
“We don’t know yet whether differences in maternal behavior can lead to differences in infant development. Because orangutans need years of development, we need at least more than a decade to accumulate the data needed to study the impact of these differences on infant development,” Schuppli said.
This study also raises interesting questions about the evolutionary origins of parenting styles. Consistent differences in maternal behavior may have fitness consequences, which can affect the speed at which offspring can reach development milestones and their future reproductive success.
With Sumatra orangutans seriously endangered, understanding the nuances of their maternal behavior has greater significance for conservation efforts. As their habitat continues to shrink, insights into the complexity of their social development and parenting patterns may help inform conservation strategies for this vulnerable species.
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