Scientists already knew that orangutans normally nurse their young for six to seven years. However, new research, published in the May 2017 issue of the journal Science Advances, extends the timeline of this nursing behavior by at least another year. Evidence from barium levels in monkey molars indicates that orangutan mothers continue to supplement a young orangutan’s solid food diet for many years. Most primates provide milk for a certain period of time and then decrease milk production when the pup begins to eat solid food. However, the new dental analysis shows that after childhood, barium levels increased about once a year, probably during seasons when fruits and insects were less abundant.
Keeping young orangutans fed:
“We found the first evidence of a seasonal pattern of rising and falling milk consumption over several years,” says study lead author Tanya Smith.
The researchers analyzed orangutan molars from four young Borneo and Sumatran orangutans, looking for biochemical signs of lactation, specifically signs of barium in breast milk.
Because orangutans are so solitary, biologists have great difficulty observing them nursing their babies. Orangutan mothers find private, hard-to-see spots in the trees, and typically nurse their young at night.