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Written by Stephanie Boehm, Phys.org
Capuchin monkeys use sticks to search the ground for food. Capuchin Culture Project in Scientific Reports (2024). DOI: 10.1038/s41598-024-61243-8
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Capuchin monkeys use sticks to search the ground for food. Capuchin Culture Project in Scientific Reports (2024). DOI: 10.1038/s41598-024-61243-8
Capuchin monkeys are omnivores, and in the wild their diet includes buds, flowers, leaves, seeds, nuts, fruits, and berries. The same goes for birds, eggs, small mammals, molluscs, and arthropods such as insects and spiders.
Some of these food sources are found underground, and tools could allow monkeys to find and access them. Wild chimpanzees (Pan troglodytes) are known to use sticks to dig underground plant storage organs (bulbs, corms, taproots, tubers), but how do capuchin monkeys obtain food from underground? There is little research on.
A research team from the University of São Paulo, the Capuchin Monkey Culture Project in Brazil, the Max Planck Institute for Animal Behavior and the Max Planck Institute for Evolutionary Anthropology in Germany, has discovered that the bearded capuchin monkey (Sapajus libidinosus, formerly known as Cebus libidinosus) was found in the wild. We investigated how they live. Underground food sources. A paper describing the team's findings has been published in Scientific Reports.
Sticks and stones as tools for capuchin monkeys
Bearded capuchin monkeys are known for using rocks as hammers to crack open wrapped fruits and nuts.
A 2009 study found that in Brazil's Capybara Mountains National Park, an arid savannah region, people use stones to find and access subterranean food and “habitually modify sticks and use sticks as probes. This is the first report on the observation of a population of bearded capuchin monkeys in the dry savannah region known as “the savannah.” “They bathe for honey, expel prey (lizards, bees, scorpions, etc.) from rock crevices and trunks, and sometimes seek other resources,” the Scientific Reports paper states.
Credit: Scientific Reports Capuchin Culture Project (2024). DOI: 10.1038/s41598-024-61243-8
Importantly, this new study provides the first report of bearded capuchin monkeys using sticks as probes to find food underground. Researchers in the new study spent 21 months observing a group of bearded capuchin monkeys in Brazil's Ubajara National Park, a humid savannah region.
Of the 31 individuals in the group (adults and subadults only, no juveniles), the researchers found that the monkeys were able to dig underground using only tools or hands to collect trapdoor spiders (Idiops sertania and Neodiplothele sp.). A total of 214 cases of digging were recorded. ) and an underground storage organ, described in the paper as “a tuberous root with a reddish-brown skin that monkeys peel off with their hands and teeth before eating the meat.”
Looking at the usage status of stone tools in numbers
The monkeys used tools selected from a group of 50 stone tools in just over half of their digging attempts (51.4%), giving them a success rate of 31.8%. Using only the hands had more success (40.4%). Stone was used in 59% of the attempts to excavate underground storage organs, and in 48% of his attempts to dig spider burrows.
Tools used by capuchin monkeys in Uvajala National Park. (a) Stick tool used to investigate trapdoor spiders. (b) Drilling stones used to excavate underground food. Scale: 10cm. Credit: Scientific Reports (2024). DOI: 10.1038/s41598-024-61243-8
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Tools used by capuchin monkeys in Uvajara National Park. (a) Stick tool used to investigate trapdoor spiders. (b) Drilling stones used to excavate underground food. Scale: 10cm. Credit: Scientific Reports (2024). DOI: 10.1038/s41598-024-61243-8 (a, b) Underground storage organs excavated by researchers during the wet period in the same location excavated by capuchin monkeys. The roots of this plant species are reddish. Although we have not been able to identify the species yet, it is morphologically similar to the Fariña Seca USO (Thloa glaucocarpa) excavated by capuchin monkeys in Capybara Mountains National Park. Credit: Scientific Reports (2024). DOI: 10.1038/s41598-024-61243-8
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(a, b) Underground storage organs excavated by researchers during the humid period in the same location excavated by capuchin monkeys. The roots of this plant species are reddish. Although we have not been able to identify the species yet, it is morphologically similar to the Fariña Seca USO (Thloa glaucocarpa) excavated by capuchin monkeys in Capybara Mountains National Park. Credit: Scientific Reports (2024). DOI: 10.1038/s41598-024-61243-8
The researchers observed that monkeys used stone tools in 59% of hill mines, but only 24% of riverbank mines. Although men used stone tools more frequently than women, the gender of stone tool users did not play a role in the success of their attempts.
Most of the stone tools were made of sandstone and were “much smaller and lighter (average weight 128 g) than the pounding tools used by the same group to crack open palm fruits (average weight 1,142 g),” the researchers report. are doing.
How to use the stick tool by number
In the 40 recorded attempts, the monkey used a stick on the ground and was successful on 42.5% of its attempts. Of these 40 of his specimens, 32 were specifically targeted at trapdoor spider burrows. The other eight targets were unknown because researchers either did not have access to the rugged excavation site or were unable to locate the remains of the monkeys. In nearly half (47.5%) of these digging attempts, the monkeys used multiple sticks.
Monkeys used sticks to dig on riverbanks almost twice as often (63%) than in hills, and of the 30 stick tools the researchers measured, they had an average total length of 29.4 cm and an average total thickness. was 2.9mm.
(a) A trapdoor spider of the species Idiops sertania (family Idiopidae) eaten by a capuchin monkey in UNP. (b, c) Burrows are usually located in valleys with trapdoors camouflaged in the surrounding ground. (d) Trapdoor spider of the species Neodiplothele sp. (family Barychelidae, species not yet described) consumed by capuchin monkeys. (e) Its morphology is not very robust and it may lose some of its legs during the exploration process (some legs are found inside the burrow after an exploration episode). (f, g) They also build burrows in valleys, especially riverbanks, and camouflage their trapdoors into the surrounding ground. Credit: Scientific Reports (2024). DOI: 10.1038/s41598-024-61243-8
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(a) A trapdoor spider of the species Idiops sertania (family Idiopidae) eaten by a capuchin monkey in UNP. (b, c) Burrows are usually located in valleys, with trapdoors camouflaged in the surrounding ground. (d) Trapdoor spider of the species Neodiplothele sp. (family Barychelidae, species not yet described) consumed by capuchin monkeys. (e) Its morphology is not very robust and it may lose some of its legs during the exploration process (some legs are found inside the burrow after an exploration episode). (f, g) They also build burrows in valleys, especially riverbanks, and camouflage their trapdoors into the surrounding ground. Credit: Scientific Reports (2024). DOI: 10.1038/s41598-024-61243-8
Techniques for catching spiders
The researchers observed that the monkeys used four techniques to capture trapdoor spiders. Monkeys also used two methods to reach underground storage organs: “hands only” and “digging through stones.”
In the case of spiders, monkeys were further observed using 'stick probing'. First, they used their hands to remove the gill cover covering the spider's burrow, then inserted a twig and swung it from side to side, pushing the spider out so they could capture the spider and perhaps remove the ootheca (egg mass) as well. Probably.
The fourth spider burrowing technique was the “stone stick,” in which the monkeys first used stone tools to minimize the depth of the burrow, and then used the stick to probe inside and remove spiders and egg sacs.
Other potential effects on drilling operations
This paper discusses in detail how other factors such as wet and dry seasons can influence different drilling behaviors and considers soil cohesiveness.
Furthermore, this study presents a comprehensive comparison of the behavior of capuchin monkeys observed in the present study in Ubajara National Park with that observed in a previous study conducted in Serra da Capibara National Park. , suggesting that differences in group culture may play a role in the observed behavior.
This type of research is important to “better understand the ecological pressures that may have shaped the emergence of different drilling tools and techniques in primate lineages,” the researchers concluded. There is.
Further information: Tatiane Valença et al. Wild capuchin monkeys use stones and sticks to access underground food, Scientific Reports (2024). DOI: 10.1038/s41598-024-61243-8
Magazine information: Scientific Reports
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