Monkey Forest Tales: Group formation mechanisms in monkeys

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In my last post, we talk about two new observations made during this birth season, the possible fission of a large group of Colombian squirrel monkeys and the possibly new formation of a group of dusky titi monkeys.

After a conversation with one of the landowners in the area where he asked if that was good or not for the monkeys in the area, I decided to explain a bit more about the mechanisms of group formation in monkeys and what it means for the monkeys in the study area.

Monkey’s groups form in two main different ways:

  1. Because one big group is so big that the competition between individuals inside the group is high and as a mechanism to reduce this competition, the groups splits, and two new groups are formed. Sometimes this group division is accompanied by a division of the original home range or territory too. This is what we seem to be happening in the study area with one of the Colombian squirrel monkey’s groups.


  1. Because of a new pair of a female and a male mate and form a new reproductive unit. This is usually the case in monogamous species such as the dusky titi monkey.

Formation of new groups of monkeys can potentially mean an increase of the monkey’s population in the area only if those new groups produce new individuals that also reproduce themselves.

So for now, in the case of the Colombian squirrel monkeys, it is possible that the population in the area is increasing not only because of the group that we had been monitoring over the past 15 years have maintained its size and grow itself but also because we had observed new groups in the vicinity. However, this needs to be monitored with caution as the changing dynamic of the area. Those new groups could also be displaced groups from other nearby forest fragments where habitat quality has been reduced and food scarcity had led to those groups to move farther.

In the case of the dusky titi monkeys, we will need to wait for the next birth season to see if this new group establish itself and have babies. The number of groups of dusky titi monkeys in the area had remained stable over the past years and only sporadically we had seen individuals dispersing outside of the focal forest fragments. More data could be necessary to say with confidence if the population is increasing in the area.

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