Revisiting the definition of animal tool use

Protracted development of stick tool use skills extends into adulthood in wild western chimpanzees

Tool use is considered a driving force behind the evolution of brain expansion and prolonged juvenile dependency in the hominin lineage. However, it remains rare across animals, possibly due to inherent constraints related to manual dexterity and cognitive abilities. In our study, we investigated the ontogeny of tool use in chimpanzees (Pan troglodytes), a species known for its extensive and flexible tool use behavior. We observed 70 wild chimpanzees across all ages and analyzed 1,460 stick use events filmed in the Taï National Park, Côte d'Ivoire during the chimpanzee attempts to retrieve high-nutrient, but difficult-to-access, foods. We found that chimpanzees increasingly utilized hand grips employing more than 1 independent digit as they matured. Such hand grips emerged at the age of 2, became predominant and fully functional at the age of 6, and ubiquitous at the age of 15, enhancing task accuracy. Adults adjusted their hand grip based on the specific task at hand, favoring power grips for pounding actions and intermediate grips that combine power and precision, for others. Highly protracted development of suitable actions to acquire hidden (i.e., larvae) compared to non-hidden (i.e., nut kernel) food was evident, with adult skill levels achieved only after 15 years, suggesting a pronounced cognitive learning component to task success. The prolonged time required for cognitive assimilation compared to neuromotor control points to selection pressure favoring the retention of learning capacities into adulthood.

Proto-tool use for food processing in wild Arabian babblers: matching processing methods, substrates and prey types

Cognition is a powerful adaptation, enabling animals to utilise resources that are unavailable without manipulation. Tool use and food processing are examples of using cognition to overcome the protective mechanisms of food resources. Here, we describe and examine the flexibility of proto-tool use (defined as the alteration of an object through object-substrate manipulation) for food processing in a cooperatively breeding bird, the Arabian babbler (Argya squamiceps). Field observations demonstrate that the birds transport different caterpillar species to different substrate types depending on the processing method needed to prepare the caterpillar for eating. Species with toxic setae (e.g. Casama innotata) are transported to be rubbed on rough substrates (e.g. sand) before consumption, while other species (e.g. Hyles livornica) are transported to be pounded against hard substrates until their inner organs are removed and only their external body part is consumed. These results are among the few to describe flexible proto-tool use for food processing in wild animals. They thereby contribute to the taxonomic mapping of proto-tool use and food processing in non-human species, which is a fundamental step to advance comparative studies on the evolution of these behaviours and their underlying cognitive mechanisms.

Object use in insects

Insects are the most diverse group of organisms in the animal kingdom, and some species exhibit complex social behaviors. Although research on insect object use is still in its early stages, insects have already been shown to display rich object-use behaviors. This review focuses on patterns and behavioral flexibility in insect object-use behavior, and the role of cultural evolution in the development of object-use behaviors. Object use in insects is not widespread but has been documented in a diverse set of taxa. Some insects can use objects flexibly and display various object-use patterns. Like mammals and birds, insects use objects in diverse activities, including foraging, predator defense, courtship, and play. Intelligence, pre-existing manipulative behaviors, and anatomical structure affect innovations in object use. In addition, learning and imitation are the main mechanisms underlying the spread of object-use behaviors within populations. Given that insects are one of the major animal groups engaging in object use, studies of insect object use could provide general insights into object use in the animal kingdom.

Robot tool use: A survey

Using human tools can significantly benefit robots in many application domains. Such ability would allow robots to solve problems that they were unable to without tools. However, robot tool use is a challenging task. Tool use was initially considered to be the ability that distinguishes human beings from other animals. We identify three skills required for robot tool use: perception, manipulation, and high-level cognition skills. While both general manipulation tasks and tool use tasks require the same level of perception accuracy, there are unique manipulation and cognition challenges in robot tool use. In this survey, we first define robot tool use. The definition highlighted the skills required for robot tool use. The skills coincide with an affordance model which defined a three-way relation between actions, objects, and effects. We also compile a taxonomy of robot tool use with insights from animal tool use literature. Our definition and taxonomy lay a theoretical foundation for future robot tool use studies and also serve as practical guidelines for robot tool use applications. We first categorize tool use based on the context of the task. The contexts are highly similar for the same task (e.g., cutting) in non-causal tool use, while the contexts for causal tool use are diverse. We further categorize causal tool use based on the task complexity suggested in animal tool use studies into single-manipulation tool use and multiple-manipulation tool use. Single-manipulation tool use are sub-categorized based on tool features and prior experiences of tool use. This type of tool may be considered as building blocks of causal tool use. Multiple-manipulation tool use combines these building blocks in different ways. The different combinations categorize multiple-manipulation tool use. Moreover, we identify different skills required in each sub-type in the taxonomy. We then review previous studies on robot tool use based on the taxonomy and describe how the relations are learned in these studies. We conclude with a discussion of the current applications of robot tool use and open questions to address future robot tool use.

A robust tool kit: First report of tool use in captive crested capuchin monkeys (Sapajus robustus)

Primate tool use is of great interest but has been reported only in a limited number of species. Here we report tool use in crested capuchin monkeys (Sapajus robustus), an almost completely unstudied robust capuchin species. Crested capuchins and their sister species, the yellow-breasted capuchin, diverged from a common ancestor over 2 million years ago, so this study fills a significant gap in understanding of tool use capacity and variation within the robust capuchin monkey radiation. Our study group was a captive population of seven individuals at the Santa Ana Zoo in California. The monkeys were given no prior training, and they were provided with a variety of enrichment items, including materials that could be used as tools as well as hard-to-access resources, for open-ended interactions. In 54 observation hours, monkeys performed eleven tool use actions: digging, hammering, probing, raking, sponging, striking, sweeping, throwing, waving, wedging, and wiping. We observed tool modification, serial tool use, and social learning opportunities, including monkeys' direct observation of tool use and tolerated scrounging of foods obtained through tool use. We also observed significant individual skew in tool use frequency, with one individual using tools daily, and two individuals never using tools during the study. While crested capuchins have never been reported to use tools in the wild, our findings provide evidence for the species' capacity and propensity for tool use, highlighting the urgent need for research on this understudied, endangered primate. By providing detailed data on clearly identified S. robustus individuals, this study marks an effort to counteract the overgeneralization in the captive literature in referring to any robust capuchins of unknown provenance or ancestry as Cebus apella, a practice that obfuscates potential differences among species in tool use performance and repertoire in one of the only species-rich tool-using genera in the world.

Tool Use in Horses

Simple Summary

Tool use has not yet been confirmed in horses, mules or donkeys. As this subject is difficult to research with conventional methods, we used crowdsourcing to gather data. We asked equid owners and carers to report and video examples of “unusual” behaviour via a dedicated website, and we searched YouTube and Facebook for videos of equids showing tools. From 635 reports, including 1014 actions, we found 13 unambiguous cases of tool use. Tool use was associated with restricted management conditions in 12 of the 13 cases, and 8 of the 13 cases involved other equids or humans. The most frequent tool use, with seven examples, was for foraging, for example, equids using sticks to scrape hay into reach. There were four cases of tool use for social purposes, such as horses using brushes to groom others, just one case of tool use for escape, in which a horse threw a halter when it wished to be turned out, and one case of tool use for comfort, in which a horse scratched his abdomen with a stick. Equids therefore can develop tool use, especially when management conditions are restricted, but it is rare.

Abstract

Tool use has not yet been confirmed in horses, mules or donkeys. As this subject is difficult to research with conventional methods, we used a crowdsourcing approach to gather data. We contacted equid owners and carers and asked them to report and video examples of “unusual” behaviour via a dedicated website. We also searched YouTube and Facebook for videos of equids showing tool use. From 635 reports, including 1014 behaviours, we found 20 cases of tool use, 13 of which were unambiguous in that it was clear that the behaviour was not trained, caused by reduced welfare, incidental or accidental. We then assessed (a) the effect of management conditions on tool use and (b) whether the animals used tools alone, or socially, involving other equids or humans. We found that management restrictions were associated with corresponding tool use in 12 of the 13 cases (p = 0.01), e.g., equids using sticks to scrape hay within reach when feed was restricted. Furthermore, 8 of the 13 cases involved other equids or humans, such as horses using brushes to groom others. The most frequent tool use was for foraging, with seven examples, tool use for social purposes was seen in four cases, and there was just one case of tool use for escape. There was just one case of tool use for comfort, and in this instance, there were no management restrictions. Equids therefore can develop tool use, especially when management conditions are restricted, but it is a rare occurrence.

Training of Motion Control May Not Improve Tool-Manipulation Ability in Rats (Rattus norvegicus)

In recent times, previous studies have reported the manipulation of tools by rats and degus in controlled experimental settings. However, a previous study reported that only one out of eight experimentally naïve rats could manipulate a rake-shaped tool according to the position of a food reward without prior experience of obtaining the reward with the tool before the test. The present study aimed to improve the training of rats and investigate rodents’ ability to manipulate tools according to food position. Stricter criteria were employed when training the rats to promote the rats’ monitoring of their own tool manipulation. Additional training was introduced to give them the opportunity to learn that the reward moved closer to them by pulling an object connected to the reward. The present study showed that only one of eight rats could manipulate a tool according to the position of the reward without prior experience of obtaining the reward with the tool or perceiving that part of the tool came in contact with the reward, as the previous study showed. The change in training did not enhance the rats’ tool-manipulation ability according to the food position. These procedures should be conducted in a wider variety of animals to investigate whether the training in motion control can promote the subjects’ effective tool-use behavior.

Surfactant affects the tool use behavior of foraging ants

Surfactants are commonly used in detergents, soaps and agrichemical products. After use, the residual surfactants can be dispersed into environmental compartments, directly or indirectly affecting aquatic and terrestrial organisms. Ants are one of the few insects that are able to make and use tools when foraging for liquid food. However, this unique behavior of ants may be greatly affected by environmental pollutants. Here, we hypothesized that surfactants have adversarial impacts on ant foraging behavior, and tested this hypothesis by investigating the effect of TWEEN 80 (a common nonionic surfactant) on the tool use behavior of black imported fire ants (Solenopsis richteri) when foraging for liquid food (sugar water). Natural pine needles and man-made sponges were provided as tools for ants. The results revealed increasing surfactant concentration induced ants to deposit more tools and caused a higher drowning rate of ants. S. richteri tended to deposit more pine needles and tools of smaller size when exposed to surfactant. Interactions between tool type and surfactant concentration showed significant effects on tool deposition and drowning rate of ants. Addition of surfactant into sugar water increased the drowning rate and reduced the foraging activity and food collection of ant workers, suggesting that surfactant in liquid food can affect the foraging efficiency of ants. However, availability of tools reduced drowning rate and increased sugar water collected compared to without tools. Our results demonstrated that ants can adjust their tool use strategies to manage the foraging risk caused by environmental surfactant, such as increasing the amount and selecting appropriate size of the tools and assembling tools of different structures. Therefore, long-term exposure to surfactants may alter foraging behavior of ants and contribute to evolve new foraging strategy.

One Function One Tool? A Review on Mutual Exclusivity in Tool Use Learning in Human and Non-human Species

The goal of this review is twofold: first to explore whether mutual exclusivity and functional fixedness overlap and what might be their respective specificities and second, to investigate whether mutual exclusivity as an inferential principle could be applied in other domains than language and whether it can be found in non-human species. In order to do that, we first give an overview of the representative studies of each phenomenon. We then analyze papers on tool use learning in children that studied or observed one of these phenomena. We argue that, despite their common principle -one tool one function- mutual exclusivity and functional fixedness are two distinct phenomena and need to be addressed separately in order to fully understand the mechanisms underlying social learning and cognition. In addition, mutual exclusivity appears to be applicable in other domains than language learning, namely tool use learning and is also found in non-human species when learning symbols and tools.

Extending the Reach of Tooling Theory: A Neurocognitive and Phylogenetic Perspective

Tool use research has suffered from a lack of consistent theoretical frameworks. There is a plethora of tool use definitions and the most widespread ones are so inclusive that the behaviors that fall under them arguably do not have much in common. The situation is aggravated by the prevalence of anecdotes, which have played an undue role in the literature. In order to provide a more rigorous foundation for research and to advance our understanding of the interrelation between tool use and cognition, we suggest the adoption of Fragaszy and Mangalam's (2018) tooling framework, which is characterized by the creation of a body-plus-object system that manages a mechanical interface between tool and surface. Tooling is limited to a narrower suite of behaviors than tool use, which might facilitate its neurocognitive investigation. Indeed, evidence in the literature indicates that tooling has distinct neurocognitive underpinnings not shared by other activities typically classified as tool use, at least in primates. In order to understand the extent of tooling incidences in previous research, we systematically surveyed the comprehensive tool use catalog by Shumaker et al. (2011). We identified 201 tool use submodes, of which only 81 could be classified as tooling, and the majority of the tool use examples across species were poorly supported by evidence. Furthermore, tooling appears to be phylogenetically less widespread than tool use, with the greatest variability found in the primate order. However, in order to confirm these findings and to understand the evolution and neurocognitive mechanisms of tooling, more systematic research will be required in the future, particularly with currently underrepresented taxa.

Dog Stick Chewing: An Overlooked Instance of Tool Use?

Tool use is a central topic in research on cognitive evolution and behavioral ecology in non-human animals. Originally thought to be a uniquely human phenomenon, many other species have been observed making and using tools for a variety of purposes, starting with Goodall's (1964) groundbreaking work with chimpanzees in Gombe. Despite the frequent attention and great research interest in animal tool use, and ubiquity of the behavior, we argue here that chewing sticks by dogs (and other animals) should be included as a case of tool use. We discuss alternate possible explanations and then propose several testable predictions regarding this hypothesis. We suggest that tool use may be more common than is often assumed and that many cases of animal tool use may be overlooked.

Honey bees (Apis cerana) use animal feces as a tool to defend colonies against group attack by giant hornets (Vespa soror)

Honey bees (genus Apis) are well known for the impressive suite of nest defenses they have evolved to protect their abundant stockpiles of food and the large colonies they sustain. In Asia, honey bees have evolved under tremendous predatory pressure from social wasps in the genus Vespa, the most formidable of which are the giant hornets that attack colonies in groups, kill adult defenders, and prey on brood. We document for the first time an extraordinary collective defense used by Apis cerana against the giant hornet Vespa soror. In response to attack by V. soror, A. cerana workers foraged for and applied spots of animal feces around their nest entrances. Fecal spotting increased after colonies were exposed either to naturally occurring attacks or to chemicals that scout hornets use to target colonies for mass attack. Spotting continued for days after attacks ceased and occurred in response to V. soror, which frequently landed at and chewed on entrances to breach nests, but not Vespa velutina, a smaller hornet that rarely landed at entrances. Moderate to heavy fecal spotting suppressed attempts by V. soror to penetrate nests by lowering the incidence of multiple-hornet attacks and substantially reducing the likelihood of them approaching and chewing on entrances. We argue that A. cerana forages for animal feces because it has properties that repel this deadly predator from nest entrances, providing the first report of tool use by honey bees and the first evidence that they forage for solids that are not derived from plants. Our study describes a remarkable weapon in the already sophisticated portfolio of defenses that honey bees have evolved in response to the predatory threats they face. It also highlights the strong selective pressure honey bees will encounter if giant hornets, recently detected in western North America, become established.

Protective behavior or 'true' tool use? Scrutinizing the tool use behavior of ants

In the genus Aphaenogaster, workers use tools to transport liquid food to the colony. During this behavior, ants place or drop various kinds of debris into liquids or soft food, and then, they carry the food-soaked tools back to the nest. According to some authors, this behavior is not "true" tool use because it represents two separate processes: a defense response to cover the dangerous liquid and a transport of food. Here, we investigated the debris dropping and retrieving behavior of the ant Aphaenogaster subterranea to establish which of the two hypotheses is more probable by conducting manipulative experiments. We tested the responses of eight colonies (a) to liquid food (honey-water) and nonfood liquids (water) in different distances from the nest and (b) to nonthreatening liquids previously covered or presented as small droplets. We also tested whether the nutritional condition of colonies (i.e., starved or satiated) would affect the intensity and rate of debris dropping. Our results were consistent with the tool-using behavior hypothesis. Firstly, ants clearly differentiated between honey-water and water, and they directed more of their foraging effort toward liquids farther from the nest. Secondly, ants performed object dropping even into liquids that did not pose the danger of drowning or becoming entangled. Lastly, the nutritional condition of colonies had a significant effect on the intensity and rate of object dropping, but in the opposite direction than we expected. Our results suggest that the foraging behavior of A. subterranea is more complex than that predicted by the two-component behavior hypothesis and deserves to be considered as "true" tool use.

Neural Processes Underlying Tool Use in Humans, Macaques, and Corvids

It was thought that tool use in animals is an adaptive specialization. Recent studies, however, have shown that some non-tool-users, such as rooks and jays, can use and manufacture tools in laboratory settings. Despite the abundant evidence of tool use in corvids, little is known about the neural mechanisms underlying tool use in this family of birds. This review summarizes the current knowledge on the neural processes underlying tool use in humans, macaques and corvids. We suggest a possible neural network for tool use in macaques and hope this might inspire research to discover a similar brain network in corvids. We hope to establish a framework to elucidate the neural mechanisms that supported the convergent evolution of tool use in birds and mammals.

Shells as 'extended architecture': to escape isolation, social hermit crabs choose shells with the right external architecture

Animals’ cognitive abilities can be tested by allowing them to choose between alternatives, with only one alternative offering the correct solution to a novel problem. Hermit crabs are evolutionarily specialized to navigate while carrying a shell, with alternative shells representing different forms of ‘extended architecture’, which effectively change the extent of physical space an individual occupies in the world. It is unknown whether individuals can choose such architecture to solve novel navigational problems. Here, we designed an experiment in which social hermit crabs (Coenobita compressus) had to choose between two alternative shells to solve a novel problem: escaping solitary confinement. Using X-ray microtomography and 3D-printing, we copied preferred shell types and then made artificial alterations to their inner or outer shell architecture, designing only some shells to have the correct architectural fit for escaping the opening of an isolated crab’s enclosure. In our ‘escape artist’ experimental design, crabs had to choose an otherwise less preferred shell, since only this shell had the right external architecture to allow the crab to free itself from isolation. Across multiple experiments, crabs were willing to forgo preferred shells and choose less preferred shells that enabled them to escape, suggesting these animals can solve novel navigational problems with extended architecture. Yet, it remains unclear if individuals solved this problem through trial-and-error or were aware of the deeper connection between escape and exterior shell architecture. Our experiments offer a foundation for further explorations of physical, social, and spatial cognition within the context of extended architecture.

Data-Driven Inference Reveals Distinct and Conserved Dynamic Pathways of Tool Use Emergence across Animal Taxa

Tool use is a striking aspect of animal behavior, but it is hard to infer how the capacity for different types of tool use emerged across animal taxa. Here we address this question with HyperTraPS, a statistical approach that uses contemporary observations to infer the likely orderings in which different types of tool use (digging, reaching, and more) were historically acquired. Strikingly, despite differences linked to environment and family, many similarities in these appear across animal taxa, suggesting some universality in the process of tool use acquisition across different animals and environments. Four broad classes of tool use are supported, progressing from simple object manipulations (acquired relatively early) to more complex interactions and abstractions (acquired relatively late or not at all). This data-driven, comparative approach supports existing and suggests new mechanistic hypotheses, predicts future and possible unobserved behaviors, and sheds light on patterns of tool use emergence across animals.

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Historical pathways of tool use acquisition inferred from large catalog of data

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Striking similarities in acquisition pathways across environments and lineages

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Acquisitions of different modes of tool use broadly follow conceptual complexity

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Wild/domestic differences and predictions of future/unobserved behaviors quantified

Evidence of tool use in a seabird

Documenting novel cases of tool use in wild animals can inform our understanding of the evolutionary drivers of the behavior’s emergence in the natural world. We describe a previously unknown tool-use behavior for wild birds, so far only documented in the wild in primates and elephants. We observed 2 Atlantic puffins at their breeding colonies, one in Wales and the other in Iceland (the latter captured on camera), spontaneously using a small wooden stick to scratch their bodies. The importance of these observations is 3-fold. First, while to date only a single form of body-care-related tool use has been recorded in wild birds (anting), our finding shows that the wild avian tool-use repertoire is wider than previously thought and extends to contexts other than food extraction. Second, we expand the taxonomic breadth of tool use to include another group of birds, seabirds, and a different suborder (Lari). Third, our independent observations span a distance of more than 1,700 km, suggesting that occasional tool use may be widespread in this group, and that seabirds’ physical cognition may have been underestimated.

Extraction without tooling around — The first comprehensive description of the foraging- and socio-ecology of wild Goffin’s cockatoos (Cacatua goffiniana)

When tested under laboratory conditions, Goffin’s cockatoos (Cacatua goffiniana) demonstrate numerous sophisticated cognitive skills. Most importantly, this species has shown the ability to manufacture and use tools. However, little is known about the ecology of these cockatoos, endemic to the Tanimbar Islands in Indonesia. Here we provide first insights into the feeding- and socio-ecology of the wild Goffin’s cockatoos and propose potential links between their behaviour in natural settings and their advanced problem-solving capacities shown in captivity. Observational data suggests that Goffin’s cockatoos rely on a large variety of partially seasonal resources. Furthermore, several food types require different extraction techniques. These ecological and behavioural characteristics fall in line with current hypotheses regarding the evolution of complex cognition and innovativeness. We discuss how the efficiency of (extractive) foraging may preclude tool use in wild Goffin’s cockatoos, even though the corresponding cognitive and ecological prerequisites seem to be present.

Non-foraging tool use in European Honey-buzzards: An experimental test

Examples of tool-use behaviors by birds outside foraging contexts are scarce and limited to a handful of species. We report a field experiment aimed to test whether an observed suite of odd behaviors by European Honey-buzzards (Pernis apivorus) represents use of green twigs cut from trees and woody shrubs as a tool to attract ants for anting. Specifically, we tested whether buzzards are selective in their choice of twigs, under the assumption that birds would prefer easy-to-collect twigs from plants that effectively attract ants. Experimental results lend support to our hypothesis that European Honey-buzzards cut green twigs of Montpellier maple trees (Acer monspessulanum) and, to a lesser extent, of Pyrenean oaks (Quercus pyrenaica) for their immediate use as ant attractors. Fresh twigs of both tree species attracted large numbers of ants, suggesting that their preferential use in the reported behavior of Honey-buzzards is not a random selection of the available plant material. Maple twigs, however, were the easiest to break and oak twigs the hardest compared to other plants in the community. This suggests that the relative ease of cracking of maple twigs may account for the preference Honey-buzzards have for this plant species as compared with Pyrenean oak, whose twigs demand considerable more effort from the birds to break. Our results lend support to the inclusion of the reported behavioral sequence by this raptor species as a potential example of tool use in birds outside the usual foraging context.

Sea Urchins as an Inspiration for Robotic Designs

Neuromorphic engineering is the approach to intelligent machine design inspired by nature. Here, we outline possible robotic design principles derived from the neural and motor systems of sea urchins (Echinoida). Firstly, we review the neurobiology and locomotor systems of sea urchins, with a comparative emphasis on differences to animals with a more centralized nervous system. We discuss the functioning and enervation of the tube feet, pedicellariae, and spines, including the limited autonomy of these structures. We outline the design principles behind the sea urchin nervous system. We discuss the current approaches of adapting these principles to robotics, such as sucker-like structures inspired by tube feet and a robotic adaptation of the sea urchin jaw, as well as future directions and possible limitations to using these principles in robots.

Habitual tool use innovated by free-living New Zealand kea

The emergence of flexible tool use is rare in the animal kingdom and thought to be largely constrained by either cognitive ability or ecological factors. That mostly birds with a high level of intelligence innovate tool use in captivity is consistent with the former hypothesis. We report here the first documented case of habitual tool use innovated in the wild by a bird species only known to have used tools in captivity. Trap-boxes containing food-bait and snap-trap(s) were installed in the remote Murchison Mountains, New Zealand, from 2002 to catch introduced stoats. Kea tampered with the trap-boxes in various ways. Over approximately 2.5 years, sticks were found inserted into at least 227 different trap-boxes that were up to 27 km apart. Video footage confirmed that the stick insertion was kea tool use. Trap-boxes are unlikely to have provided the only possibility for kea tool use in their habitat given their extractive foraging and skilled object manipulation. We argue that they instead greatly facilitated the opportunity for tool use, thus increasing the chance that kea would invent the behaviour. The innovation of tool use by kea in response to facilitation provides rare field support for the cognitive constraints hypothesis.

Tool manipulation by rats (Rattus norvegicus) according to the position of food

Tool-use behaviour has been observed in nonhuman animals in the wild and in experimental settings. In the present study, we investigated whether rats (Rattus norvegicus) could manipulate a tool according to the position of food to obtain the food in an experimental setting. Eight rats were trained to use a rake-shaped tool to obtain food beyond their reach using a step-by-step protocol in the initial training period. Following training, the rake was placed at the centre of the experimental apparatus, and food was placed on either the left or right side of the rake. Rats learned to manipulate the rake to obtain food in situations in which they could not obtain the food just by pulling the rake perpendicularly to themselves. Our findings thus indicate that the rat is a potential animal model to investigate the behavioural and neural mechanisms of tool-use behaviour.

Extraction of honey from underground bee nests by central African chimpanzees (Pan troglodytes troglodytes) in Loango National Park, Gabon: Techniques and individual differences

A detailed analysis of tool use behaviors can disclose the underlying cognitive traits of the users. We investigated the technique used by wild chimpanzees to extract the underground nests of stingless bees (Meliplebeia lendliana), which represent a hard-to-reach resource given their highly undetectable location. Using remote-sensor camera trap footage, we analyzed 151 visits to 50 different bee nests by 18 adult chimpanzees of both sexes. We quantified the degree of complexity and flexibility of this technique by looking at the behavioral repertoire and at its structural organization. We used Generalized Linear Mixed Models to test whether individuals differed in their action repertoire sizes and in their action sequencing patterns, as well as in their preferences of use of different behavioral elements (namely, actions, and grip types). We found that subjects showed non-randomly organized sequences of actions and that the occurrence of certain actions was predicted by the type of the previous action in the sequences. Subjects did not differ in their repertoire sizes, and all used extractive actions involving tools more often than manual digging. As for the type of grip employed, the grip involving the coordinated use of hands and feet together was most frequently used by all subjects when perforating, and we detected significant individual preferences in this domain. Overall, we describe a highly complex and flexible extractive technique, and propose the existence of inter-individual variation in it. We discuss our results in the light of the evolution of higher cognitive abilities in the human lineage.

Object-Tool-Actor Interaction: Object Information Drives Intended Action

Tool use is typically explored via actor-tool interactions. However, the target-object (that which is being acted on) may influence perceived action possibilities and thereby guide action. Three different tool-target-object pairings were tested (Experiment 1). The hammering action demonstrated the greatest sensitivity and therefore subsequently used to further investigate target-object pairings. The hammer was removed as an option and instructions were provided using pictorial (Experiment 2), written (Experiment 3), and both pictorial and written formats (Experiment 4). The designed tool is chosen when available (Experiment 1) and when removed as a choice (i.e., the hammer), participants perform the same action associated with the designed tool (i.e., hammering) regardless of instruction method (Experiments 2, 3, and 4).

Darwin's finches treat their feathers with a natural repellent

Darwin's finches are highly innovative. Recently we recorded for the first time a behavioural innovation in Darwin's finches outside the foraging context: individuals of four species rubbed leaves of the endemic tree Psidium galapageium on their feathers. We hypothesised that this behaviour serves to repel ectoparasites and tested the repellency of P. galapageium leaf extracts against parasites that negatively affect the fitness of Darwin's finches, namely mosquitoes and the invasive hematophagous fly Philornis downsi. Mosquitoes transmit pathogens which have recently been introduced by humans and the larvae of the fly suck blood from nestlings and incubating females. Our experimental evidence demonstrates that P. galapageium leaf extracts repel both mosquitoes and adult P. downsi and also inhibit the growth of P. downsi larvae. It is therefore possible that finches use this plant to repel ectopoarasites.

Tool-use by rats (Rattus norvegicus): tool-choice based on tool features

In the present study, we investigated whether rats (Rattus norvegicus) could be trained to use tools in an experimental setting. In Experiment 1, we investigated whether rats became able to choose appropriate hook-shaped tools to obtain food based on the spatial arrangements of the tool and food, similar to tests conducted in non-human primates and birds. With training, the rats were able to choose the appropriate hooks. In Experiments 2 and 3, we conducted transfer tests with novel tools. The rats had to choose between a functional and non-functional rake-shaped tool in these experiments. In Experiment 2, the tools differed from those of Experiment 1 in terms of shape, color, and texture. In Experiment 3, there was a contradiction between the appearance and the functionality of these tools. The rats could obtain the food with a functional rake with a transparent blade but could not obtain food with a non-functional rake with an opaque soft blade. All rats chose the functional over the non-functional rakes in Experiment 2, but none of the rats chose the functional rake in Experiment 3. Thus, the rats were able to choose the functional rakes only when there was no contradiction between the appearance and functionality of the tools. These results suggest that rats understand the spatial and physical relationships between the tool, food, and self when there was no such contradiction.

"Juggling" Behavior in Wild Hainan Gibbons, a New Finding in Nonhuman Primates

Many species of primates use tools and manipulate objects. Environmental objects, such as sticks and branches, are used in locomotion, display, conflict, nesting, and foraging. This study presents observations regarding endangered male Hainan gibbons (Nomascus hainanus) selecting sticks and then throwing and catching them repeatedly. This act of Hainan gibbons was termed as "juggling" behavior. This study is the first record of branch use of this kind in free-living gibbons. While it is impossible to experiment on this only remaining population of Hainan gibbons, the deliberate acquisition and then throwing and catching of a stick raises myriad questions regarding their function. The study determined that the juggling behavior of Hainan gibbons, in the process of their brachiation, helps them accurately judge the distance and support strength of an object. It was also found that an adult individual's proficiency in juggling behavior was much higher than that of a youth. Of all gibbon species, the juggling behavior of Hainan gibbon has a high degree of behavior refinement. Gibbons have the longest forearm than any other primates, which helps them in such performances-a unique mechanism that allows them to perform such unique activities, including juggling.

Asian elephants acquire inaccessible food by blowing

Many animals acquire otherwise inaccessible food with the aid of sticks and occasionally water. As an exception, some reports suggest that elephants manipulate breathing through their trunks to acquire inaccessible food. Here, we report on two female Asian elephants (Elephas maximus) in Kamine Zoo, Japan, who regularly blew to drive food within their reach. We experimentally investigated this behaviour by placing foods in inaccessible places. The elephants blew the food until it came within accessible range. Once the food was within range, the elephants were increasingly less likely to blow as the distance to the food became shorter. One subject manipulated her blowing duration based on food distance: longer when the food was distant. These results suggest that the elephants used their breath to achieve goals: that is, they used it not only to retrieve the food but also to fine-tune the food position for easy grasping. We also observed individual differences in the elephants' aptitude for this technique, which altered the efficiency of food acquisition. Thus, we added a new example of spontaneous behaviour for achieving a goal in animals. The use of breath to drive food is probably unique to elephants, with their dexterous trunks and familiarity with manipulating the act of blowing, which is commonly employed for self-comfort and acoustic communication.

Tool-use-associated sound in the evolution of language

Proponents of the motor theory of language evolution have primarily focused on the visual domain and communication through observation of movements. In the present paper, it is hypothesized that the production and perception of sound, particularly of incidental sound of locomotion (ISOL) and tool-use sound (TUS), also contributed. Human bipedalism resulted in rhythmic and more predictable ISOL. It has been proposed that this stimulated the evolution of musical abilities, auditory working memory, and abilities to produce complex vocalizations and to mimic natural sounds. Since the human brain proficiently extracts information about objects and events from the sounds they produce, TUS, and mimicry of TUS, might have achieved an iconic function. The prevalence of sound symbolism in many extant languages supports this idea. Self-produced TUS activates multimodal brain processing (motor neurons, hearing, proprioception, touch, vision), and TUS stimulates primate audiovisual mirror neurons, which is likely to stimulate the development of association chains. Tool use and auditory gestures involve motor processing of the forelimbs, which is associated with the evolution of vertebrate vocal communication. The production, perception, and mimicry of TUS may have resulted in a limited number of vocalizations or protowords that were associated with tool use. A new way to communicate about tools, especially when out of sight, would have had selective advantage. A gradual change in acoustic properties and/or meaning could have resulted in arbitrariness and an expanded repertoire of words. Humans have been increasingly exposed to TUS over millions of years, coinciding with the period during which spoken language evolved. ISOL and tool-use-related sound are worth further exploration.

Do bimanual coordination, tool use, and body posture contribute equally to hand preferences in bonobos?

Approximately 90% of the human population is right-handed. The emergence of this hand preference in humans is thought to be linked to the ability to execute complex tasks and habitual bipedalism. In order to test these hypotheses, the present study explored, for the first time, hand preference in relation to both body posture (seated and bipedal) and task complexity (bimanual coordination and two tool use tasks of different complexity) in bonobos (Pan paniscus). Few studies have explored the effects of both posture and task complexity on handedness, and investigations with bonobos are scarce, particularly studies on tool use. Our study aims to overcome such a gap by addressing two main questions: 1) Does a bipedal posture increase the strength of hand preference and/or create a directional bias to the use of the right hand? 2) Independent of body posture, does task complexity increase the strength of the hand preference and/or create a directional bias to the use of the right hand? Our results show that independent of body posture, the more complex the task, the more lateralization occurred. Moreover, subjects tended to be right-handed for tasks involving tool use. However, posture had no significant effect on hand preference in the tasks tested here. Therefore, for a given task, bonobos were not more lateralized in a bipedal posture than in a seated one. Task complexity might thus have contributed more than bipedal posture to the emergence of human lateralization and the preponderance of right-handedness, although a larger sample size and more data are needed to be conclusive.

A validated set of tool pictures with matched objects and non-objects for laterality research

Neuropsychological and neuroimaging research has established that knowledge related to tool use and tool recognition is lateralized to the left cerebral hemisphere. Recently, behavioural studies with the visual half-field technique have confirmed the lateralization. A limitation of this research was that different sets of stimuli had to be used for the comparison of tools to other objects and objects to non-objects. Therefore, we developed a new set of stimuli containing matched triplets of tools, other objects and non-objects. With the new stimulus set, we successfully replicated the findings of no visual field advantage for objects in an object recognition task combined with a significant right visual field advantage for tools in a tool recognition task. The set of stimuli is available as supplemental data to this article.