Some baby monkeys develop faster than others in the same population, and this is best explained by the threat of infanticide they face from adult males, says a study.
"Infanticide occurs in many animals, including carnivores like lions and bears, rodents like mice, and in primates," said lead researcher Iulia Badescu from University of Toronto.
"Typically, an adult male kills an infant sired by another male so that he can mate with the mother and sire his own infants with her," Badescu noted.
In this study that appeared online in the journal Animal Behaviour, the researchers looked at infant development in wild ursine colobus monkeys.
Black-and-white colobus includes several species of medium-sized monkeys found throughout equatorial Africa.
They have black bodies with white hair that sometimes forms a bushy white beard and sideburns, or can extend down the back like a 'cape' and down the tail.
Colobus babies are born pure white and their coat colour changes to grey after a few weeks before turning black-and-white between two and five months.
The researchers were intrigued by the fact that infants varied in the age at which their coats became grey, and then black and white.
They also realised that these colour transitions were helpful to track the development of the infants, in a non-intrusive fashion.
Earlier research at the study site, Boabeng-Fiema Monkey Sanctuary in Ghana, established that some scenarios are more likely to lead to infanticide by males. Groups with multiple males, for example, have more instances of infanticide.
The team observed nine groups of ursine colobus monkeys in the wild over a period of eight years (2007 to 2014).
"We found that infants facing a greater risk of infanticide developed faster than infants facing lesser risk," Pascale Sicotte, professor at University of Calgary in Canada, explained.
