Orangutans prove to be exceptionally awesome moms. One proof: they nurse longer than any other mammal, sometimes into the ninth year of life.

New study findings showed that previous estimates of wild orangutan mothers nursing their offspring for up to seven years may be low. The pattern could actually last up to eight or nine years, particularly when young orangutans would supplement their diet with breast milk during times of food scarcity.

Long Nursing Journey For Orangutans

The late weaning, said lead author Tanya Smith of Griffith University, is likely a technique to survive.

“Having a long period of nursing may be a way for juveniles to learn the ins and outs of living in a challenging environment with limited and unpredictable food resources," Smith explained in an NPR report.

Orangutans in the wild are notoriously difficult to study, living solitary lives up in the trees of Borneo and Sumatran rainforests. These new results therefore lend greater insight into their nursing behavior.

What the team did to acquire more information was to analyze teeth from dead orangutans in museum collections. They recreated four orangutans’ nursing history via an analysis of barium, an element absorbed from a mother’s milk, in teeth samples.

Teeth record the events happening in one’s body every day, said study author and researcher Christine Austin. Just like trees, they boast of growth rings that offer a timeline of animal lives.

In the study, barium levels in every ring indicated when a given orangutan was ingesting milk. They demonstrated that in the first 12 to 18 months of life, young orangutans consumed only breast milk, followed gradually by fruit and other foods.

The youngsters, however, returned to nursing when there was inadequate food supply, with the cyclical nursing patterns continuing until puberty knocked.

Animal And Human Weaning

In comparison, chimpanzees wean the young at 5 years of age, while gorillas stop nursing once their offspring reach age 4.

Human babies, of course, barely get breast-fed after they turn 3 or so. This tendency to switch babies to other food earlier in life allows humans to produce more babies, shared paleoanthropologist Shara Bailey.

It largely remains unclear when early weaning became commonplace. It could have occurred almost a million years earlier just as humans began controlling fire, or some 10,000 years past when agricultural practices started.

Weaning, though, may not necessarily follow a “linear progression” from reliance on breast milk to independence, anthropology assistant professor Laurie Reitsema told NYT. As the new study suggested, the activity could actually be “a series of pulses” throughout an orangutan’s lifespan.

One factor for the drastic variance in orangutan feeding could be mast fruiting, where massive numbers of trees fruit at once regardless of season. These take place every two to six years and could become quite unpredictable, said Cheryl Knott of Boston University.

There’s also a perceived link between extended nursing in orangutans and the species’ extinction potential at current levels of habitat loss and poaching. These apes may be far more vulnerable than we thought, explained Smith, and that their populations’ struggle may root from their need for so long to transition from a baby to another.

Orangutans are endangered since they are quite slow to reproduce, where females wait until they are 10 or 15 in order to reproduce. At most, they give birth once every five years, and understanding the workings of nursing and breastfeeding could help better protect them.

The findings have been detailed in the journal Science Advances.