KeywordsTriadic Interaction Gestural Communication Young Bull Social Tool Social Target
A tool directed toward another animal (social target) or the use of another animal as a tool (social means).
Tool use in nonhuman animals takes many forms. Social tool use consists of two different categories. Social-target tool use involves an animal using a tool toward or for the purpose of another animal. For instance, a male gila woodpecker often fed his offspring with honey, but this proved difficult when the honey was thinned down. He then removed pieces of bark and dipped them in the honey, which allowed him to transport it to his offspring. Thus, the bark was a tool that functioned to transport a liquid to a social target. The second category is social-means tool use: using another animal as a tool. For example, African elephant bulls have been observed to pick up and throw young bulls at fences, which broke and consequently enabled the bulls to pass. The young bulls were used as throwing tools. Some cases involve both social-target and social-means tool use, such as when a chimpanzee hits another chimpanzee with a dead colobus monkey (examples from Shumaker et al. 2011).
Based on Shumaker et al.’s (2011) general definition of tool use, social-target tool use is the external employment of an unattached or manipulable attached environmental object to alter more efficiently the form, position, or condition of another animal (not the user itself), when the user holds and directly manipulates the tool during or prior to use and is responsible for the proper and effective orientation of the tool. Social-means tool use is the external employment of another manipulable animal (the tool) to alter more efficiently the form, position, or condition of another object, another organism, or the user itself, when the user holds and directly manipulates the tool during or prior to use and is responsible for the proper and effective orientation of the tool.
The majority of tool-use modes can be social-target tools and social-means tools. Some modes even require a social target, such as using a tool to stab, beat or entice others. Tools can also be used to create or augment a display, which clearly has a social component. However, our definition excludes certain behaviors that are sometimes regarded as social tool use (e.g., Johnson 2010; Völter et al. 2015) because the tool is not physically manipulated by the user. Examples of excluded behaviors are social learning of tool use, material culture, recruitment, communication, deception, tool sharing, and cooperation. Nonetheless, this distinction is not absolute and is only based on their typical aspects. For instance, communication may involve social tool use when an object is used to create or augment a social display.
Social-Target Tool Use
One of the most common types of social-target tool use is agonistic dropping or throwing. Some bird species and most primates appear to do this, with the exception of prosimians (Hunt et al. 2013; Shumaker et al. 2011). It is sometimes argued that only aimed throwing and dropping should be considered tool use, but this is often difficult to determine. Moreover, throwing and dropping may have the same function whether aimed or not; they can effectively intimidate, threaten, or displace others (Osvath and Karvonen 2012). Some unaimed dropping and throwing appears to be stereotyped displacement, or originates from it, which could then have developed into aimed social-target tool use (Hunt et al. 2013).
Not all chimpanzees are habitual projectile throwers. Only 39 out of 91 chimpanzees threw consistently in one group. Those that did had greater cortical connectivity in areas of the brain that are associated with motor control and speech production in humans. These differences were mainly present in the brain hemisphere opposite to their preferred throwing hand, which was also the hand they mostly used in other tool tasks and gestural communication. This contralateral brain-limb association is likewise typical for humans. Chimpanzees that had learned to throw scored better on tests of communicative abilities than those that did not. There were no differences in performance on other tests of social and physical cognition. Both throwing and gestural communication serve to alter the behavior of others, although it is unclear whether one is the result of the other (Hopkins et al. 2012).
Social-Means Tool Use
Using another animal as a tool seems to be rarer than social-target tool use. In one case, a large troop of Japanese macaques was provided with food in a long transparent tube. They were conditioned to use stick tools, and some learned to throw stones to push the food out. Other macaques often waited at the far end of the tube so they could steal the food if a tool user threw a stone against it. The tube was wide enough for infants to enter, and two females pulled back theirs if they spontaneously crawled into the tube and collected the food. Another female used all four of her infants as social-means tools by actively pushing them into the tube and pulling them back once they retrieved the food. The advantages of this tool use are that the tool was always available, in contrast to sticks and stones that could be burrowed under snow, and that scroungers could not wait at the other end of the tube to steal the food (Tokida et al. 1994).
Orangutans can also use their offspring as social tools. In one experiment food was placed behind a barrier with holes too small for the hands of adults. Each of three orangutan females frequently used their juvenile offspring as tools by moving them toward the barrier, pushing their hands through a hole, or pulling their arms once they grabbed the food. Similarly, when food was placed behind a small door opening, the mothers pushed the juveniles through, held on to their limbs, and pulled them back as soon as they retrieved the food. They then took the food from them. Similar results were found when the goal was a tool that could be used to retrieve inaccessible food, which shows that orangutans can use tools sequentially with the first tool being a social-means tool. In forced choice experiments, the juveniles preferred to take the food but were often coerced by their mothers to take a tool that they then used to retrieve preferred food. They were also sometimes moved through the narrow door opening if they could use a tool there to obtain food for themselves and their mothers (Völter et al. 2015). Orangutans also throw objects at dogs and even pull humans toward a goal so they can use them as ladders (Köhler 1993). These experiments show that orangutan can adjust their behavior flexibly by using others as social tools.
Social-Means-Target Tool Use
A triadic interaction is necessary when both social tool use types are combined. The user manipulates another animal as a tool to affect a third animal in social-means-target tool use. However, it does not follow that all triadic interactions involve social tool use, as some researchers have claimed (e.g., Johnson 2010), when the user does not physically manipulate the tool. One type of triadic interaction that does involve social tool use is agonistic buffering, in which an animal uses another animal as a tool to discourage attacks from an aggressive target. Primates such as macaques, baboons, bonobos, and chimpanzees sometimes hold infants to inhibit potentially agonistic interactions. In some cases they instead used infants to get third parties to follow them or elicit affiliation from them (Johnson 2010; Parker and Gibson 1977; Shumaker et al. 2011).
A very different kind of social-means-target tool use is found in boxer crabs. They hold small stinging anemones in their claws and use them to catch food. They also use these anemones as protection against threats or as weapons in fights with other crabs. This behavior mostly encompasses twitching, waving, and extending the anemones. Contacting other crabs with anemones only rarely occurs. Fights are often ritualized in many animal species, which include the weapon use of boxer crabs that could inflict serious damage on contact (Karplus et al. 1998).
Social tool use can involve cognitive complexity that is traditionally only associated with nonsocial tool use. Although learning socially to use tools and the psychological manipulation of others are interesting behavioral categories, they should be seen as distinct from social tool use because the user exerts no direct physical control over the purported tool, which is instead regarded as a self-propelled agent. With our operational definition, social tool use can be investigated as being both a social and tool-related behavior, which offers unique avenues for future research.
- Hopkins, W. D., Russell, J. L., & Schaeffer, J. A. (2012). The neural and cognitive correlates of aimed throwing in chimpanzees: A magnetic resonance image and behavioural study on a unique form of social tool use. Philosophical Transactions of the Royal Society B, 367, 37–47. doi:10.1098/rstb.2011.0195.CrossRefGoogle Scholar
- Johnson, C. M. (2010). Observing cognitive complexity in primates and cetaceans. International Journal of Comparative Psychology, 23, 587–624.Google Scholar
- Karplus, I., Fiedler, G. C., & Ramcharan, P. (1998). The intraspecific fighting behavior of the Hawaiian boxer crab, Lybia edmondsoni – Fighting with dangerous weapons? Symbiosis, 24, 287–302.Google Scholar
- Köhler, W. (1993). The mentality of orangs. International Journal of Comparative Psychology, 6, 189–229.Google Scholar
- Shumaker, R. W., Walkup, K. R., & Beck, B. B. (2011). Animal tool behavior: The use and manufacture of tools by animals. Baltimore: JHU Press.Google Scholar