By Dr. Becker
Sadly, twins born to animals in the wild usually die within a short time after birth, or only one of the pair grows to adulthood.
It would seem the presence of two newborns is simply too heavy a burden on a female primate in the wild.
The only non-human primates known to be consistently successful at parenting twins is a group of South American monkeys called the Callitrichidae, which includes marmosets and tamarins.
Females in this primate family often have twins, and the males are very involved in childrearing.
Sometimes male and female parents even raise triplets together.
The Secret to Successful Mothering of Twins
Because the existence of primate twins in the wild is so rare, the birth two years ago of male twins to a free-ranging Tibetan macaque at Huangshan, China became the subject of a research project.
Male Tibetan macaques, like many other male primates, play no role in parenting offspring.
And female macaques are known to mate with more than one male during mating season, so paternity is often a question mark.
According to Megan Matheson, one of the study co-authors, "Generally speaking, in these species where paternity uncertainty is the norm, adult males will be protective of all infants if they are threatened, but don't necessarily favor any one for special contact."
The mother was studied for five months after she gave birth. Her behavior and activities were compared to those of other adult females with just one or no offspring.
The researchers noted she spent more time foraging and resting than the other females, but she still managed to spend quality time socializing. It seemed she liked to show off her twins, though she tended to push one into the spotlight more often than the other.
Some female primates play the role of aunt to the offspring of other females in the group, but this isn't common behavior with Tibetan macaques. Matheson theorizes it is because macaque mothers encourage their youngsters to be independent. They don't hover protectively over their offspring like other female primates.
Clearly, when it comes to Tibetan macaques, mother monkeys bear full responsibility for shepherding their youngsters to adulthood.
So How Did She Do?
In addition to managing her time to allow for maximum foraging opportunities, socializing, and periods of rest, the macaque mother also insisted on nursing both babies at the same time to conserve physical energy. If one arrived ahead of the other to be fed, she would refuse to nurse him until his brother arrived.
All in all, the mother macaque seemed imminently qualified for the task of raising twins. According to study co-author Matheson:
"She appeared to remain quite healthy. I was very impressed when I observed her in August of 2010 running with two, by now quite large, infants hanging on!"
The last time the researchers checked in on the group, the macaque twins were still alive. They were not quite two years old and still considered young juveniles. Male macaques don't reach full adulthood until seven years of age.
The researchers' conclusion:
Our report provides a case of successfully surviving twins in a wild environment and suggests that the mother modified her behavior patterns to adapt to the heavy burden. We conclude that both food provisioning and the mother's behavioral strategies facilitated the survivorship of twins. This expands our understanding of the reproductive biology of Tibetan macaques.