Squirrel monkeys are small enough to go on the smallest branches to get food.
"I don't think it was a squirrel monkey," she said.
In 2012, a male squirrel monkey called Charlie was rescued.
They live next door to the squirrel monkeys together with Jethro.
The common squirrel monkey uses different types of calls for specific situations.
He and his colleagues ran a test in which they offered squirrel monkeys a choice between one piece of date or four.
Later studies showed squirrel monkeys were also vulnerable to infection.
The group tends to sleep in the same trees every night for months at a time, unlike other squirrel monkeys.
All other squirrel monkeys that hear the alarm call also dive for cover.
Studies have shown that the squirrel monkeys' most common calls are determined by their genetics.