Threat Test

Monkeys in Ecuador can distinguish threatening humans from those who don’t pose a significant danger, according to a study in PLOS ONE.

Reacting to potential predators takes a toll on animals. For example, the prey animal might cut a meal short or become stressed. But if the animal can assess the threat level of a specific human, it won’t waste energy avoiding people who aren’t particularly dangerous.

The researchers observed seven groups of woolly monkeys in two parts of Yasuni National Park, Ecuador. One site is frequently-hunted, and the other site is not. Locals sometimes gather plants in the forest, and scientists conduct studies there as well.

Upon encountering each group of monkeys, a team member behaved like a hunter, gatherer, or researcher. To act like a hunter, the person remained silent and carried a blowpipe, which locals often use to shoot poisoned darts at monkeys. To simulate a gatherer, the person made more noise, collected plants, and ignored the animals. And the “researcher” behavior included looking at the monkeys and carrying equipment such as a notebook, binoculars, and video camera.

After spotting the “hunter,” the monkeys became quieter, travelled less, and were less likely to be seen. At the heavily-hunted site, “the next strongest response was to humans behaving as gatherers… and the least pronounced response was to the researcher condition,” the authors write. They conclude that the monkeys’ ability to distinguish dangerous from more benign people “may allow them to conserve both time and energy when encountering humans which pose no threat.” Roberta Kwok | 17 April 2013

Source: Papworth, S., E.J. Milner-Gulland, and K. Slocombe. 2013. Hunted woolly monkeys (Lagothrix poeppigii) show threat-sensitive responses to human presence. PLOS ONE doi: 10.1371/journal.pone.0062000.

Image © Ammit Jack |