The chimps that never forget: ‘It is impressive that they remember where the ants are’

The secret camera is activated, a sign that a wild animal has passed in front of it. It is dry season and Hiila, a savannah chimpanzee, walks determinedly towards her target. She stops, pushes aside a layer of dry leaves with her hand, puts her nose to the ground and inserts a finger into a small hole. Bad luck, no ants this time. So how did she know there was an ant hill there?

The question is addressed by a study carried out by the Jane Goodall Institute Spain (IJGE) and the University of Barcelona (UB), recently published in the journal Communications Biology. In 2009, in Dindefelo, Senegal, the team installed secret cameras to learn more about the chimpanzees they are trying to protect. One of the main aims of this research is to understand how these animals manage to survive in Dindefelo’s challenging environment.

Although we tend to associate chimpanzees with dense rainforests, conditions are very different in the savannahs of West Africa. Hardly a drop of rain falls for seven months at a time. The vast grasslands dry out and trees that are not near water sources lose their leaves. It is a place of heat and dust, where the only shelter is offered by the forests along riverbanks, known as gallery forests. When the rains finally come, many areas are flooded and yellow gives way to green. In a matter of days, the landscape is completely transformed.

In the dry season, chimpanzees take advantage of any available food resource, even if accessing it can be complicated or even painful, as is the case with legionnaire ants. Unlike termites, which build visible mounds of earth, these ants live in underground ant hills, which makes them difficult to locate. They also have a particular fondness for climbing up warm bodies until they reach the genitals. By the time they take their first bite, the animal is covered in them.

In Dindefelo, ant hills are rare and mostly found in gallery forests. The IJGE had set up some of its cameras in these areas, succeeding for the first time in recording chimpanzees feeding on legionnaire ants. This led to a key question: how did they manage to exploit such a risky resource?

Andreu Sánchez Megías traveled to Dindefelo to investigate as part of his master’s thesis. As he explains to EL PAÍS, the use of tools is key: “They make tools with branches that they strip. Sometimes they also modify the ends by tearing off the bark with their mouths. Once they get the perfect stick, they insert it into the hole where the ants are. They repeatedly pull it in and out until a sufficient number of ants climb up the stick. Then they pull it out and eat the ants.”

The study allowed the research team to observe that some chimpanzees visited the same ant hills repeatedly over time. Hiila was one of the most insistent chimpanzees. During the course of the study, which lasted for five years, she went to the same ant hill on 25 days. “Sometimes the ants stay for days in the same place, even though the chimps have gone on successive days to eat them,” says Sánchez Megías. “They risk being attacked by the chimps, but they prefer to stay in that spot because it’s hard to find another one. They have to be constantly weighing things up,” he adds.

However, it is also common for these insects to leave their home temporarily. For example, during the wet season, ant hills may flood, forcing the ants to move. The following year, they may return to the same location. Despite these changes, the chimpanzees return again and again to the ant hills. “It is impressive that they remember the exact spots where the ants are, because they are not visible to the naked eye,” says Adriana Hernández-Aguilar, co-director of research at the IJGE, seconded by Serra Húnter professor at the UB.

In several videos, Hiila comes to the ant hill accompanied by her offspring. According to Hernández-Aguilar, social learning could play a crucial role in this behavior. “Although it is very difficult to demonstrate that mothers actively teach their children, they do teach passively, enacting behaviors for their young to observe. Just as the babies learn the best places to sleep, they might also learn where the ants are and how to get them.”

In some cases, chimpanzees arrived at the ant hill carrying the tool they were going to use in their mouths. According to Josep Call, Professor of Evolutionary Origins of Mind at the University of St. Andrews, this tendency is particularly interesting: “On the one hand, the anticipated transport of tools suggests that they not only remember that there is food there, but also the type of food they are going to find. This ability has been demonstrated on multiple occasions in captivity, but is less frequently observed in the wild,” says Call.

These observations gleaned from the study are relevant to understanding the evolution of intelligence, including human intelligence. Early hominins are thought to have inhabited environments similar to Dindefelo, and these seasonal habitats are often associated with the development of complex cognitive abilities in primates. “It is possible that substantial changes in the environment make it difficult to remember places where food has been found in the past. This would perhaps lead species to develop a more consistent memory. For example, based on spatial (right/left) rather than figurative (green/brown) aspects, which would not be as affected by external shifts brought about by climatic changes,” Call explains.

According to Hernández-Aguilar, the study highlights the importance of the insect diet in the cognitive development of primates, especially those living in the savannah. “Dindefelo chimpanzees hunt monkeys, although this is not common. Most of their protein comes from insects. These food sources are essential to them, not only for their protein supply, but also for their mineral content. During the dry season, temperatures are very high, and they need minerals as much as we do,” he says.

The main objective of the IJGE in Senegal is to prevent the extinction of chimpanzees. The research conducted at Dindefelo not only provides information on the behavior and cognitive abilities of these primates but also helps to identify the key resources they need to survive in this extreme habitat. This is vitally important for the correct adjustment of conservation efforts.

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