2023 Author: Bryan Walter | [email protected]. Last modified: 2023-05-21 22:24
A Sumatran Orangutan (Pongo abelii) female with a calf at Gunung Löser National Park
Orangutans are the only primates, with the exception of humans, that are able to communicate past events to others, Science Advances says. After the female orangutans saw the predators, they sounded an alarm, delayed in time by seven minutes.
Until now, it was believed that primates, with the exception of humans, are not able to transmit information to their relatives about something remote in time or space. Although some primates, such as vervet, emit an alarm in the absence of predators, researchers believe that this is a tactical ploy, and not a reference to past events. Moreover, different species of primates emit alarms for different reasons, not necessarily in response to the appearance of a predator, and their relatives interpret and react to them in different ways, so until now primatologists could not determine with certainty whether monkeys are using references to past events. …
Psychologists Adriano Lameira and Josep Call of St Andrews University have found that some monkeys do use delayed alarms. Scientists have observed female Sumtran orangutans (Pongo abelii) living in the Ketamba forest in the north of the island. They showed seven females and their calves four models of predators with different skin colors - brindle, painted in abstract colors, spotted and pure white. The researchers put on bags imitating skins and approached a tree on which an orangutan was sitting 5-20 meters above the ground. Two minutes later, the "predators" left, and the authors of the article followed the reaction of the monkeys. In total, scientists conducted 24 experiments, five females were shown all four "predators" once, and two "predators" were shown to two.
Tiger model shown to orangutans
In half of the cases, orangutans emitted a delayed alarm. Immediately after they saw the predator, the monkeys grabbed the cub and climbed higher. And, on average, after seven minutes, they made a series of smacking sounds - an alarm. One of the females after the disappearance of the "predator" was silent for 17 minutes before reporting the danger. Moreover, the orangutans continued to issue alarm signals for quite a long time, on average for 25 minutes.
Researchers have proposed and rejected several explanations for the behavior of orangutans. So, scientists consider it unlikely that the monkeys were so numb with fear that they could not make a sound. After they saw the predator, the monkeys immediately began to climb higher up the tree and defecate in the process (a sign of stress). In addition, if the females were silent out of fear, then it is likely that scientists would have noticed a correlation between the age of the monkey and the time that elapsed between the appearance of the "predator" and the alarm. Older and more experienced individuals would react faster.
Also, scientists dismissed the assumption that monkeys reported danger to their relatives. Orangutans are the only great apes that live alone rather than in flocks. Each mother and calf have their own territory in which they feed, and the females practically do not intersect with each other. Although the sounds the orangutans made could be heard from about 300 meters away, the other orangutans did not respond to them.
The researchers suggested that the orangutans were initially silent so as not to attract the attention of the predator, and with the help of a delayed alarm signal, the mother taught her cub to properly respond to danger. Since orangutans are solitary monkeys, their cubs stay with their mother longer than the cubs of other primates, on average up to 8-9 years old, it is the mother who teaches them everything. Therefore, the researchers suggested that if the mother was silent after the disappearance of the danger, the cub would not be able to learn the correct behavior in such a situation.
The researchers acknowledge that their hypothesis is nothing more than a working hypothesis and requires more research. At the same time, they note that it may well turn out to be true. First, orangutan pups older than three years old (and the youngest calf in the researchers' sample was five years old) can already divide their attention among several objects. Second, it is likely that the cubs, in addition to sound signals, perceived information multimodally: they observed the direction of the mother's gaze, her posture, and muscle tension. In addition, there is now growing evidence that primates have episodic memories and memories of previous events. Therefore, the authors of the study suggest, it is likely that orangutan cubs can learn something from a delayed alarm.
Recently, scientists have found that captive orangutans have learned how to make hooks out of wire, or, conversely, unbend the wire in order to use it to get food from pipes of various shapes. A few years ago, it turned out that a female orangutan, also living in captivity, learned how to make a hammock from a piece of cloth.