These monkeys would have Darwin scratching his head.
Why would a mother want to kill her offspring? That question lies at the center of a study published in the journal Primates that looks at mother mustached tamarins.
Mother tamarins do not have an easy job. Gestation is long — about 150 days; they usually have twins, and those twins are usually big. It's up to the mother to carry that double load around until the babies are old enough to navigate the forest canopy themselves. The only thing that makes the work tolerable is that tamarin troops cooperate to rear young, but the conditions have to be right. There must be plenty of males to do the protecting and provisioning, and there can't be too many other females with babies of their own that also require attention.
The researchers found that 75 percent of infants survive when at least three males are helping, but only 41.7 per cent survive if the group has one or two male helpers, according to the Daily Mail
In essence, mother mustached tamarin's kill their babies when they are unlikely to survive, due to a low number of helpers and the presence of another gestating female.
These primates "have a cooperative baby care system, in which all the members of the group participate." Infants only survive when the whole group works together.
Only one female mustached tamarin can successfully reproduce in each group.