Nick Carne
Female chimpanzees with high-ranking mothers are more likely to be homebodies, according to analysis of data from the famous Gombe National Park in Tanzania.
It appears the benefits of having a built-in support system can outweigh the risks of inbreeding with male relatives, which often occurs because of a brother’s misdirected advances.
Leaving is not without its own risks – notably being attacked by resident females when you arrive in a new group. Despite this, while males spend their entire lives where they were born, cooperating to defend their territory, female chimps tend to move around.
But some don’t, which has intrigued Anna Pusey, from Duke University in the US, since she started working in Gombe with Jane Goodall in 1970.
She and colleagues noticed the pattern back then, but female chimps don’t leave home until they are at least 11, so it would take years of observation to unravel the reasons behind it.
Now Pusey has digitised 45 years of dawn-to-dusk observations for 31 female chimpanzees born in Gombe, and studied the data with another US primatologist, Kara Walker from North Carolina State University.
Writing in the journal Current Biology, they report finding little difference between females who left and those who stayed in terms of factors such as diet quality, crowding or available males, which suggests they don’t leave due to competition for food or mates.
It was only when the researchers looked more closely at the females’ family members that the split began to reveal itself. Specifically, they found that females with more brothers were more likely to leave – presumably because they risk inbreeding if they stay.
But there was a countervailing force for some females. High-ranking mothers are able to provide help, such as sharing prime foraging spots, and their social clout can provide other benefits that outweigh the risks of staying.
