Naïve chimpanzees are able to spontaneously use tools in order to excavate underground food, according to a new study, published in the journal PLoS ONE. The animals prefer longer tools for excavation and exhibit six different tool use behaviors in the context of excavation: digging, probing, perforating, pounding, shoveling and enlarging.
This study was conducted on a colony of chimpanzees (Pan troglodytes) housed at the Kristiansand Zoo in Kristiansand, Norway. Image credit: Motes-Rodrigo et al, doi: 10.1371/journal.pone.0215644.
In 2011, a team of researchers from the University of Ljubljana and Iowa State University reported that wild western chimpanzees (Pan troglodytes verus) from Bandafassi, Senegal, use tools to excavate underground food, but did not provide detail.
The only other non-human animals known to use tools to harvest underground food are bearded capuchins (Sapajus libidinosus) from Serra da Capivara National Park, Brazil.
“The discovery that wild chimpanzees and bearded capuchins use tools to excavate underground food is important because this behavior was once considered unique to hominins, one which supposedly set humans and their ancient ancestors apart from other primates,” said Dr. Alba Motes-Rodrigo from the University of Tübingen and colleagues.
“The incorporation of underground food into the hominin diet was thought to have played a critical role in human evolution because these resources were proposed to have served as fallback foods in the transition from moister, forested to drier habitats, where underground food was more abundant.”
In the new study, Dr. Motes-Rodrigo and co-authors studied tool use and selection in captive chimpanzees to further understand how food excavation behavior may have developed.
The scientists monitored a colony of ten chimpanzees living on an island enclosure at the Kristiansand Zoo in Norway, eight of whom were born in captivity and none of whom had previously performed excavating behaviors.
The team dug five small holes and placed whole fruit in each, initially leaving the holes open to alert the chimpanzees to the fruit, and later filling in each hole.
Tool use behaviors that emerged during the excavation of underground food: (A) probe, (B) perforate, (C) pound, (D) dig, (E) shovel, and (F) enlarge. Image credit: Motes-Rodrigo et al, doi: 10.1371/journal.pone.0215644.
At first, the researchers provided ready-made tree stick and bark tools; in a second experiment, they did not provide ready-made tools for excavation.
Nine of the ten chimpanzees successfully excavated buried fruit at least once, with eight chimps choosing to use tools rather than their bare hands to do so.
When the chimpanzees were not given ready-made tools, they collected their own tools from island vegetation.
The team observed the chimpanzees reusing particular tools as well as choosing long tools over shorter ones for excavation behaviors.
In addition to noting six different types of excavation behaviors, the study authors also observed chimps taking turns to excavate a hole, and even sharing the fruit once extracted.
“The results from captive chimps may not be exactly extrapolated to wild populations; and that modern apes should not be treated simply as ‘living fossil’ stand-ins for hominin ancestors,” Dr. Motes-Rodrigo and colleagues said.
“Nonetheless, early hominins may have worked out how to use simple tools to harvest underground food in a similar fashion to these chimps.”
_____
A. Motes-Rodrigo et al. 2019. Chimpanzee extractive foraging with excavating tools: Experimental modeling of the origins of human technology. PLoS ONE 14 (5): e0215644; doi: 10.1371/journal.pone.0215644