For infant chimpanzees, survival depends on a close relationship with their mother, but even after weaning, orphaned chimpanzees have significantly lower survivals rates than non-orphans, according to a recent study led by professors at Franklin & Marshall College, George Washington University and Duke University.
F&M’s Visiting Assistant Professor of Psychology Maggie Stanton and Associate Professor of Psychology Elizabeth Lonsdorf recently co-authored a paper in Behavioral Ecology and Sociobiology titled, “Consequences of maternal loss before and after weaning in male and female wild chimpanzees.” The study used data collected from the long-term study of chimpanzees in Gombe National Park, Tanzania, with support from the Jane Goodall Institute.
“Chimpanzees who are orphaned while still relying on mother’s milk for nutrition are expected to have pretty low odds of survival, but like humans, young chimpanzees remain with their mothers for years after they are done nursing,” Stanton said.
Researchers used more than 50 years of data on wild chimpanzees, collected from two communities in Gombe. They examined the survival and longevity of males and females that experienced maternal loss during three different age categories.
“We found that even older orphans – those who were orphaned after weaning and up to 10 years old in females and 15 years old in males – face lower odds of survival compared to individuals whose mothers are alive,” Stanton said.
Specifically, males orphaned between ages 0–5 years, 5–10 years, and 10–15 years faced much lower probability of survival than non-orphans and died earlier than expected. Females faced similarly reduced survival when orphaned between 0–5 and 5–10 years of age, but those who experienced maternal loss between 10 and 15 years were no more likely to die than non-orphans.
Stanton said, “These results highlight how mothers continue to matter for young chimpanzees, even as they approach adulthood.”
According to Lonsdorf, “Humans are one of only a few animals that exhibit substantial dependence on the mother after weaning. What we’ve shown here is that we share that characteristic with chimpanzees. It is only through the accumulation of long-term data, over a period of 50-plus years, that we are able to ask questions about lifespan effects on chimpanzee development and survival.”