John Mitani

Well, we initiated this project over 30 years ago in 1995 in Kibale National Park, which lies in the southwest portion of Uganda.

And the impetus for this project lay in the fact that this group was so large initially all the way back at the beginning.

But the surprising thing is that during the first 20 years of this study, the group actually continued to grow.

At its peak, it reached over 200 individuals.

Is that a lot?

That's quite a bit.

That's four times larger than the average size of other chimpanzee groups that have been studied in the wild.

And actually, the chimps here found strength in numbers and were quite successful.

They were able to dominate their neighbors by living together in such a large group.

At one point in 2009, they actually expanded their territory into areas that were previously occupied by their neighbors.

They obtained more food.

With all that food, females started to reproduce much more.

Infant survivorship went up dramatically.

In fact, again, with so much food, some females in this group lived such a long time that they experienced menopause, a finding that hadn't yet been described in chimps.

Well, chimpanzees, like many other primates, are social creatures, so they do live in social groups.

And there's a collection of individuals who live together.

They associate with one another.

They occupy a separate territory from other groups.

So there's a bounded number of individuals who live together.

And we recognize those group members.