Why are Angolan colobus infants white?
On October 20, we had a new addition to our Angolan colobus group when Adanna gave birth to her second infant. Now if you have had the chance to see her, the first thing you might notice is that she is all white. Even though adult colobus are mostly black with white shoulder and ear tufts, their infants are born completely white. When I first learned about this strange characteristic, I thought it was very odd. It was my understanding that primate infants are often a target for many predators, so why would colobus have infants that stand out so much? While no one knows exactly why they are born completely white, there is one theory that most people believe. That is that the striking color difference helps alert the other females in the troop that there has been a newborn and it helps promote a behavior called “aunting” or “alloparenting.” All this means is that the other females in the troop help raise the infant.
But this is a common behavior within primates and especially within monkeys, so why doesn’t every species have infants born with such a striking coloration difference? That’s because the aunting behavior is much more important for colobus than it is for other monkey species. Colobus are leaf-eating monkeys, meaning the majority of their diet is leaves. Unfortunately, leaves are not very nutrient-rich, so leaf-eating monkeys such as colobus monkeys have to eat a lot of leaves to get the nutrients they require. So how does that play into the babies being white? Well, as any mother out there will tell you, raising an infant is very stressful, especially on the body. Colobus mothers have to be sure they are eating enough each day so that they can counteract the burden of nursing. Taking care of an infant can be time consuming, which can make it difficult for the mother to find the time to eat enough for both her and the infant. This is where the aunting behavior becomes so important. By having the other females in the troop take time holding and caring for the infant, it allowsthe mother to have time to eat the amount she requires for nursing. So, while several species of monkeys practice the aunting behavior, it is more important in colobus monkeys because of their diet and the nutritional needs of a nursing mother.
As you can see from the adults, the infants do eventually get the black coloration. This change happens gradually as the infant gets older, and by 3 months of age the infant will have its adult coloration. While the infant may still be nursing, it should be much more independent and moving around, giving the mother the free time she needs to eat. Therefore, the need for aunting is less than before.
With this behavior comes an added benefit. By helping out the mother, it allows females that haven’t given birth yet to learn how to care for an infant and how to be a mother. You can even see our 1-year-olds, Orlando and Kito, carrying the infant from time to time. Even though they are still a couple years away from being mature enough to have kids, they are already learning how to be a mother.
Keeper I, Primates