Tool use by non-humans
Tool use by non-humans is a phenomenon in which a non-human animal uses any kind of
Among other
Several species of
Definitions and terminology
The key to identifying tool use is defining what constitutes a tool. Researchers of animal behaviour have arrived at different formulations.
In 1981, Beck published a widely used definition of tool use.[1] This has been modified to:
The external employment of an unattached or manipulable attached environmental object 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.[2]
Other, briefer definitions have been proposed:
An object carried or maintained for future use.
— Finn, Tregenza, and Norman, 2009.[3]
The use of physical objects other than the animal's own body or appendages as a means to extend the physical influence realized by the animal.
— Jones and Kamil, 1973[4]
An object that has been modified to fit a purpose ... [or] An inanimate object that one uses or modifies in some way to cause a change in the environment, thereby facilitating one's achievement of a target goal.
— Hauser, 2000[5]
Others, for example Lawick-Goodall,[6] distinguish between "tool use" and "object use".
Different terms have been given to the tool according to whether the tool is altered by the animal. If the "tool" is not held or manipulated by the animal in any way, such as an immobile anvil, objects in a bowerbird's bower, or a bird using bread as bait to catch fish,[7] it is sometimes referred to as a "proto-tool".[8]
When an animal uses a tool that acts on another tool, this has been termed use of a "meta-tool". For example, New Caledonian crows will spontaneously use a short tool to obtain an otherwise inaccessible longer tool that then allows them to extract food from a hole.[8] Similarly, bearded capuchin monkeys will use smaller stones to loosen bigger quartz pebbles embedded in conglomerate rock, which they subsequently use as tools.[9]
Rarely, animals may use one tool followed by another, for example, bearded capuchins use stones and sticks, or two stones.[9] This is called "associative", "secondary" or "sequential" tool use.[10]
Some animals use other individuals in a way which could be interpreted as tool use, for example, ants crossing water over a bridge of other ants, or
Borderline examples
Play
Play has been defined as "activity having no immediate benefits and structurally including repetitive or exaggerated actions that may be out of sequence or disordered".[12] When play is discussed in relation to manipulating objects, it is often used in association with the word "tool".[13] Some birds, notably crows, parrots and birds of prey, "play" with objects, many of them playing in flight with such items as stones, sticks and leaves, by letting them go and catching them again before they reach the ground. A few species repeatedly drop stones, apparently for the enjoyment of the sound effects.[14] Many other species of animals, both avian and non-avian, play with objects in a similar manner.[2]
Fixed "devices"
The impaling of prey on thorns by many of the
Use of bait
Several species of bird, including herons such as the striated heron (Butorides striatus), will place bread in water to attract fish.[14][17][18] Whether this is tool use is disputed because the bread is not manipulated or held by the bird.[19]
Captive orcas have been observed baiting and catching a bird with a regurgitated fish, as well as showing similar behaviour in the wild.[20][21]
Learning and cognition
Tool use by animals may indicate different levels of
In mammals
Primates
Tool use has been reported many times in both wild and captive primates, particularly the great apes. The use of tools by primates is varied and includes hunting (mammals, invertebrates, fish), collecting honey, processing food (nuts, fruits, vegetables and seeds), collecting water, weapons and shelter.
Tool manufacture is much rarer than simple tool use and probably represents higher cognitive functioning. Soon after her initial discovery of tool use, Goodall observed other chimpanzees picking up leafy twigs, stripping off the leaves and using the stems to fish for insects. This change of a leafy twig into a tool was a major discovery. Prior to this, scientists thought that only humans manufactured and used tools, and that this ability was what separated humans from other animals.[24] In 1990, it was claimed the only primate to manufacture tools in the wild was the chimpanzee.[25] However, since then, several primates have been reported as tool makers in the wild.[26]
Both bonobos and chimpanzees have been observed making "sponges" out of leaves and moss that suck up water and using these for grooming. Sumatran orangutans will take a live branch, remove twigs and leaves and sometimes the bark, before fraying or flattening the tip for use on ants or bees.
Chimpanzees and bonobos
Hunting
Research in 2007 showed that common chimpanzees sharpen sticks to use as weapons when hunting mammals. This is considered the first evidence of systematic use of weapons in a species other than humans.[34][35] Researchers documented 22 occasions when wild chimpanzees on a savanna in Senegal fashioned sticks into "spears" to hunt lesser bushbabies (Galago senegalensis).[36] In each case, a chimpanzee modified a branch by breaking off one or two ends and, frequently using its teeth, sharpened the stick. The tools, on average, were about 60 cm (24 in) long and 1.1 cm (0.4 in) in circumference. The chimpanzee then jabbed the spear into hollows in tree trunks where bushbabies sleep.[37] There was a single case in which a chimpanzee successfully extracted a bushbaby with the tool. It has been suggested that the word "spear" is an overstatement that makes the chimpanzees seem too much like early humans, and that the term "bludgeon" is more accurate, since the point of the tool may not be particularly sharp.[38] This behaviour was seen more frequently in females, particularly adolescent females, and young chimps in general, than in adult males.[35]
Chimpanzees often eat the marrow of long bones of
In
Other studies of the Gombe chimps show that young females and males learn to fish for termites differently. Female chimps learn to fish for termites earlier and better than the young males.[40] Females also spend more time fishing while at the mounds with their mothers—males spend more time playing. When they are adults, females need more termite protein because with young to care for, they cannot hunt the way males can.[41]
Populations differ in the prevalence of tool use for fishing for invertebrates. Chimpanzees in the
Some chimpanzees use tools to hunt large bees (
Chimpanzees have even been observed using two tools: a stick to dig into an ant nest and a "brush" made from grass stems with their teeth to collect the ants.[25]
Collecting honey
Honey of four bee species is eaten by chimpanzees. Groups of chimpanzees fish with sticks for the honey after having tried to remove what they can with their hands. They usually extract with their hands honeycombs from undisturbed hives of honey bees and run away from the bees to quietly eat their catch. In contrast, hives that have already been disturbed, either through the falling of the tree or because of the intervention of other predators, are cleaned of the remaining honey with fishing tools.[25]
Processing food
Tai chimpanzees crack open nuts with rocks, but there is no record of Gombe chimpanzees using rocks in this way.[24] After opening nuts by pounding with a hammer, parts of the kernels may be too difficult to reach with the teeth or fingernails, and some individuals use sticks to remove these remains, instead of pounding the nut further with the hammer as other individuals do:[25] a relatively rare combination of using two different tools. Hammers for opening nuts may be either wood or stone.[42]
Collecting water
When chimpanzees cannot reach water that has formed in hollows high up inside trees, they have been observed taking a handful of leaves, chewing them, and dipping this "sponge" into the pool to suck out the water.[41] Both bonobos and chimpanzees have also been observed making "sponges" out of leaves and moss that suck up water and are used as grooming tools.[43]
Orangutans
Orangutans were first observed using tools in the wild in 1994 in the northwest corner of Sumatra.[44] As with the chimpanzees, orangutans use tools made from branches and leaves to scratch, scrape, wipe, sponge, swat, fan, hook, probe, scoop, pry, chisel, hammer, cover, cushion and amplify. They will break off a tree branch that is about 30 cm long, snap off the twigs, fray one end and then use the stick to dig in tree holes for termites.[27][45] Sumatran orangutans use a variety of tools—up to 54 types for extracting insects or honey, and as many as 20 types for opening or preparing fruits such as the hard to access Neesia malayana.[46] They also use an 'autoerotic tool'—a stick which they use to stimulate the genitals and masturbate (both male and female).[47] There have been reports that individuals in both captivity and in the wild use tools held between the lips or teeth, rather than in the hands.[48] In captivity, orangutans have been taught to chip stone to make and use Oldowan tools.[49][50]
Orangutans living in Borneo scavenge fish that wash up along the shore and scoop catfish out of small ponds for fresh meals. Over two years, anthropologist Anne Russon observed orangutans learning to jab sticks at catfish to scare them out of the ponds and in to their waiting hands.[51] Although orangutans usually fished alone, Russon observed pairs of apes catching catfish on a few occasions.[52] On the island of Kaja in Borneo, a male orangutan was observed using a pole apparently trying to spear or bludgeon fish. This individual had seen humans fishing with spears. Although not successful, he was later able to improvise by using the pole to catch fish already trapped in the locals' fishing lines.
Sumatran orangutans use sticks to acquire seeds from a particular fruit.[53] When the fruit of the Neesia tree ripens, its hard, ridged husk softens until it falls open. Inside are seeds that are highly desirable to the orangutans, but they are surrounded by fibreglass-like hairs that are painful if eaten. A Neesia-eating orangutan will select a 12 cm stick, strip off the bark, and then carefully collect the hairs with it. Once the fruit is safe, the ape will eat the seeds using the stick or its fingers.[45] Sumatran orangutans will use a stick to poke a bees' nest wall, move it around and catch the honey.[45]
Orangutans have been observed using sticks to apparently measure the depth of water. It has been reported that orangutans use tools for a wide range of purposes including using leaves as protective gloves or napkins, using leafy branches to swat insects or gather water, and building sun or rain covers above the nests used for resting.[54] It has been reported that a Sumatran orangutan used a large leaf as an umbrella in a tropical rainstorm.[45]
Orangutans produce an alarm call known as a "kiss squeak" when they encounter a predator like a snake. Sometimes, orangutans will strip leaves from a branch and hold them in front of their mouth when making the sound. It has been found this lowers the maximum frequency of the sound i.e. makes it deeper, and in addition, smaller orangutans are more likely to use the leaves. It has been suggested they use the leaves to make themselves sound bigger than they really are, the first documented case of an animal using a tool to manipulate sound.[55]
Gorillas
There are few reports of gorillas using tools in the wild.[56] Western lowland gorillas have been observed using sticks to apparently measure the depth of water and as "walking sticks" to support their posture when crossing deeper water.[57] An adult female used a detached trunk from a small shrub as a stabiliser during food gathering, and another used a log as a bridge. One possible explanation for the absence of observed tool use in wild gorillas is that they are less dependent on foraging techniques that require the use of tools, since they exploit food resources differently from chimpanzees. Whereas chimpanzees and orangutans feeding involves tools such as hammers to crack open nuts and sticks to fish for termites, gorillas access these foods by breaking nuts with their teeth and smashing termite mounds with their hands.[58]
Captive western lowland gorillas have been observed to threaten each other with sticks and larger pieces of wood, while others use sticks for hygienic purposes. Some females have attempted to use logs as ladders.[59] In another group of captive gorillas, several individuals were observed throwing sticks and branches into a tree, apparently to knock down leaves and seeds.[60] Gorillas at Prague Zoo have used tools in several ways, including using wood wool as "slippers" when walking on the snow or to cross a wet section of the floor.[29]
Monkeys
Species | Type and Extent of Tool Use | References[61] |
---|---|---|
Red howler monkey (Alouatta seniculus) | Anecdotal evidence of a free individual using tools to be aggressive towards another | Richard-Hansen et al., 1998 |
Geoffroy's spider monkey (Ateles geoffroyi) | Multiple recorded observations of free individuals using tools for physical maintenance | Campbell, 2000; Rodriguez & Lindshield, 2007 |
White-fronted capuchin (Cebus albifrons) | Multiple recorded observations of free individuals using tools for food transportation | Phillips, 1998 |
Brown capuchin (Sapajus apella | Extensive observations of tool use including: captive, free, and semi free individuals extracting food with tools, captive individuals transporting food with a tool, and captive individuals to be aggressive towards another | Cooper & Harlow, 1961; Izawa & Mizuno, 1977; Strusaker & Leland, 1977; Antinucci & Visalberghi, 1986; Visalberghi, 1990, 1993; Fernandes, 1991; Anderson & Henneman, 1994; Westergaard & Suomi, 1994, 1995; Westergaard et al., 1995; Lavallee, 1999; Boinski et al., 2000; Cleveland et al., 2004; de A. Moura & Lee, 2004; Ottoni & Mannu, 2001; Ottoni et al., 2005; Schrauf et al., 2008 |
White-faced capuchin (Cebus capucinus) | Multiple accounts of free individuals using tools to extract food, maintain their physical self, defend against predation, and to be aggressive towards another | Bierens de Haan, 1931; Boinski, 1988; Chevalier-Skolnikoff, 1990; Baker, 1996 |
Black-striped capuchin (Sapajus libidinosus) | Multiple accounts of free individuals using tools to prepare and extract food and to perform physical maintenance. | Fragaszy et al., 2004; Waga et al., 2006; Visalberghi et al., 2007; Mannu & Ottoni, 2009 |
Wedge-capped capuchin (Cebus olivaceus) | Multiple accounts of free individuals using tools to perform physical maintenance. | Valderrama et al., 2000 |
Golden-breasted capuchin (Sapajus xanthosternus) | Multiple accounts of free individuals using tools to extract food | Canale et al., 2009 |
Sooty mangabey (Cercocebus atys) | Multiple accounts of captive individuals using tools to perform physical maintenance | Galat-Luong, 1984; Kyes, 1988 |
Agile mangabey (Cercocebus agilis) | Anecdotal evidence of a captive individual using tools to capture food | Guillaume & Meyerson, 1934 |
Red-tailed monkey (Cercopithecus ascanius) | Anecdotal evidence of a free individual using tools to perform physical maintenance | Worch, 2001 |
Vervet Monkey (Cercopithecus aethiops) | Multiple accounts of captive individuals using tools to capture food and perform physical maintenance | Galat-Luong, 1984; Pollack, 1998; Santos et al., 2006 |
Lowe's mona monkey (Cercopithecus campbelli) | Anecdotal evidence of a captive individual using a tool to perform physical maintenance. | Galat-Luong, 1984 |
Western red colobus (Colobus badius) | Multiple accounts of free individuals using tools to be aggressive towards another | Struhsaker, 1975; Starin. 1990 |
Common patas monkey (Erythrocebus patas) | Anecdotal evidence of a captive individual using tools to capture food | Gatinot, 1974 |
Long-tailed macaque (Macaca fascicularis)
|
Multiple accounts of semi free and free individuals using tools to prepare food, free individuals using tools to extract food and perform physical maintenance, and captive individuals transporting and capturing food and performing physical maintenance and other tasks | Carpenter, 1887; Chiang, 1967; Karrer, 1970; Artaud & Bertrand, 1984; Zuberbühler et al., 1996; Malaivijitnond et al., 2007; Watanabe et al., 2007; Masataka et al., 2009; Gumert et al., 2009 |
Japanese macaque (Macaca fuscata) | Multiple accounts of free individuals using tools to prepare and extract food and captive individuals capturing food | Kawai, 1965; Tokida et al., 1994; Hihara et al., 2003 |
Rhesus macaque (Macaca mulatta) | Multiple accounts of captive individuals preparing, transporting, and capturing food with tools | Shepherd, 1910; Hobhouse, 1926; Parks & Novak, 1993; Erwin, 1974 |
Pig-tailed macaque (Macaca nemestrina) | Multiple accounts of captive individuals using tools to capture food and perform physical maintenance | Beck, 1976 |
Sulawesi crested macaque (Macaca nigra)
|
Anecdotal evidence of captive individuals using tools to extract food | Babitz, 2000 |
Bonnet macaque (Macaca radiata) | Anecdotal evidence of free individuals using tools to perform physical maintenance | Sinah, 1997 |
Lion-tailed macaque (Macaca silenus) | Multiple accounts of free individuals using tools to prepare food, captive individuals to extract and transport food, and semi free individuals to transport food | Hohmann, 1988; Westergaard, 1988; Fitch-Snyder & Carter, 1993; Kumar et al., 2008 |
Tonkean macaque (Macaca tonkeana) | Multiple accounts of captive individuals using tools to extract food and perform physical maintenance, and semi free individuals using tools to capture food | Bayart, 1982; Anderson, 1985; Ueno & Fujita, 1998; Ducoing & Thierry, 2005 |
Drill (Mandrillus leucophaeus) | Anecdotal evidence of captive individuals using tools to perform physical maintenance | Armbruster, 1921; Galat-Luong, 1984 |
Mandrill (Mandrillus sphinx) | Anecdotal evidence of captive individuals using tools | Schultz 1961 |
Olive baboon (Papio anubis) | Multiple accounts of free individuals preparing, extracting, to be aggressive towards another, and performing physical maintenance with tools and of captive individuals using tools to capture food | van Lawick-Goodall et al., 1973; Pettet, 1975; Pickford, 1975; Benhar & Samuel, 1978; Oyen, 1979; Westergaard, 1992, 1993 |
Yellow baboon (Papio cynocephalus) | Anecdotal evidence of captive individuals using tools to capture food | Nellman & Trendelenburg, 1926 |
Hamadryas baboon (Papio hamadryas) | Multiple accounts of captive individuals using tools to capture food | Beck, 1972, 1973 |
Guinea baboon (Papio papio) | Multiple accounts of captive individuals using tools to capture food | Beck, 1973b; Petit & Thierry, 1993 |
Chacma baboon (Papio ursinus) | Multiple accounts of free individuals using tools to extract food and to be aggressive towards another and of captive individuals capturing food | Bolwig, 1961; Marais, 1969; Hamilton III et al., 1975 |
Silvered leaf monkey (Trachypithecus cristatus)
|
Multiple accounts of free individuals using tools to be aggressive towards another | Lydekker, 1910 |
Tool use has been observed in at least 32 monkey species [61] including individuals that are captive, free, and semi-free range. These observations entail established, long term use of tools such as baboons using items to hit humans as well as more elusive, rare use like the howler monkeys' use of leaves to treat wounds.[62] Use is further nuanced by if a species uses objects they have found or objects that they have modified. Of the 32 species that exhibit tool use, 11 of these exhibit object modification to make tools.[61]
In a captive environment, capuchins readily insert a stick into a tube containing viscous food that clings to the stick, which they then extract and lick.[63] Capuchins also use a stick to push food from the centre of a tube retrieving the food when it reaches the far end,[64] and as a rake to sweep objects or food toward themselves.[65] The black-striped capuchin (Sapajus libidinosus) was the first non-ape primate for which tool use was documented in the wild; individuals were observed cracking nuts by placing them on a stone anvil and hitting them with another large stone (hammer).[66] Similar hammer-and-anvil use has been observed in other wild capuchins including robust capuchin monkeys (genus Sapajus)[66][67][68][69][70] It may take a capuchin up to 8 years to master this skill.[71] The monkeys often transport hard fruits, stones, nuts and even oysters to an anvil for this purpose.[72] Capuchins also use stones as digging tools for probing the substrate and sometimes for excavating tubers.[9] Wild black-striped capuchin use sticks to flush prey from inside rock crevices.[9] Robust capuchins are also known to sometimes rub defensive secretions from arthropods over their bodies before eating them;[67] such secretions are believed to act as natural insecticides.
Baboons have also exhibited extensive tool use, seen within research on the chacma baboon (Papio ursinus) troops living on the desert floor of the Kuiseb Canyon in South West Africa. These baboons intentionally dropped stones over cliffs.[73] Researchers have seen other types of tool use such as raking with tools and the use of barrels to climb in baboons.[74]
Scientists have observed mandrills to modify and then use tools within captive environments.[28]
In long-tailed macaques, tool use has been extensively observed, particularly within foraging and grooming habits.[75][76] These tools have both been synthetic and organic in origin and their use varies greatly depending on populations.[77] The research done within these populations and their tool use has been used to draw conclusions that high levels of sensorimotor intelligence help evolve innovative tool use.[77]
Limitations of primate tool use
Tools used by nonhuman primates are limited in their complexity. Unlike human tools, which increase in complexity as they are passed down, nonhuman primate tools may be restricted to what has been dubbed "zones of latent solutions" (ZLS) - that is, the range of tools and techniques that can be developed independently by a species. Tools within this zone can be individually and socially learned, but tools outside this zone cannot. This renders non-human primates unable to develop tools beyond this zone, towards levels of human technology.
According to the ZLS hypothesis, every primate possesses a zone of solutions to ecological problems that can develop in interaction with a given environment, known as their zone of latent solutions.[78] This package of skills fits the primate's environment; it contains packages of potential solutions that can be realized within the primate's existing and potential behaviour. Tool use within this zone can likewise be expressed via genetic predispositions, through trial and error learning, and all this may be triggered by social learning - but this social learning does not transfer the skills themselves, as in humans. All this may lead some to the conclusion that all primates have a human-like capacity to copy abilities to make and/or use complex tools from each other. However, nonhuman primate tool use is likely constrained to those tools within each species' zone of latent solutions - unless human training expands this zone.
For example, every chimpanzee has the capacity to learn how to use sticks to capture and consume ants.[79] This behaviour is likely in the chimpanzees' ZLS, and therefore belong to every chimpanzee's potential biological toolkit. Yet, many may require a social "push", i.e. a trigger, before they themselves develop this behaviour individually. However, chimpanzees, and every other great ape, seem to be unable to learn tool use behaviour outside of their ZLS - i.e. in cases where a behaviour would not just be triggered, but copied. For example, in a 2009 experiment no species of great ape apart from humans (including chimpanzees, gorillas and orangutans) were able to spontaneously bend a flexible strip into a loop to hook and retrieve an otherwise unreachable object, under any condition, even with human teaching.[80] Since loops fall securely outside of great apes' ZLS—perhaps as there was never any use for this behaviour in their ecological environment—this behaviour is unable to be learned socially by non-human primates.
The role of culture in primate tool use
Humans navigate our material world through the lens of cultural learning. Cultural learning is defined as high-complexity social learning, where tools and behaviours are invented on top of previous inventions which have previously been copied and taught - leading to cultural refinement across generations via the so-called cultural ratchet effect.[81] As cultural animals, we regularly invent new tools based on our acquired cultural background, we may pay attention to specific models, such as the most successful individuals (and various other social learning biases), and in this way the best tool practices may increase in frequency and stick around in our collective repertoire until better designed ones are built on top.[82] This cultural learning allows human tool complexity and efficiency to "ratchet up" through cultural generations, building tools of increased complexity over time, which allows the products (behaviours and/or artefacts) to accumulate over time in a process known as "cumulative culture."[82] Nonhuman primate tools, contrarily, are unable to ratchet up in complexity over time as these animals do not copy tool design that they themselves could not have independently created from scratch, and therefore primates other than humans are restricted to those tools that reside within their zone(s) of latent solutions.[78]
While human tools and technologies currently still increase in complexity at an exponential rate, for instance evolving from stone tools to rocket ships and supercomputers within a few thousand years, nonhuman primate tools show little evidence of improvement or underlying technological change in their underlying know-how across generations. For example, archaeological evidence indicates that the basic chimpanzee nut-cracking know-how has been static for at least the past 4300 years.[78] This consistency and stasis in tool behaviour suggests that chimpanzee tools are not refined or improved across generations with a ratcheting-up effect, but rather reinvented by every single chimpanzee generation. That is, non-human primates must "re-invent the wheel" at every generation anew.
Humans differ from nonhuman primates in how we perceive tools and their underlying know-how. Humans, as a cultural species, are predisposed to copy the know-how (methods, relationships and processes) behind tools, while our nonhuman primate relatives are predisposed to instead individually innovate their tools from scratch or to be merely socially triggered to re-innovate the tools used by others (who, ultimately had to innovate them from scratch). For example, when both human children and chimpanzees (both aged 2–4 years) are shown solutions to open a box with observably unnecessary steps involved, human children consistently copy even the unnecessary steps, while chimpanzees bypass unnecessary steps and go straightforwardly to their natural tendencies of engaging with the box, such as using a stick to poke it.[83] This difference between chimpanzees and humans suggests that chimpanzees tend to see tools through the lens of their own individual approaches, while humans tend to see tools through the lens of the underlying know-how, even where their own tendencies mismatch the observed know-how. Nonhuman primates are predisposed to re-innovate technologies that already exist in their zone of latent solutions, while, as a cumulative cultural species, humans learn know-how culturally that clearly is beyond the human zone of latent solutions. Over time, and across generations, this has led humans to have culturally created billions of know-how types, with the vast majority being beyond the human zone of latent solutions. Other apes, in contrast, seem to draw from a range of know-how that counts in mere thousands.[84]
While humans and nonhuman primates are both tool users, both their expression and their capacities for tool use are vastly different. The zone(s) of latent solutions of nonhuman primates, and the cultural ratcheting-up of human technology rest on different underlying processes with vastly different capacities for complexity and improvement over time. While humans copy know-how that is supraindividual, other primates do not. It is currently unclear whether the zone of latent solutions approach is restricted to non-human primates, or whether it may also help explain tool use in many (or all) other animals. One step towards determining whether other animals' tool use is likely based on latent solutions or is instead due to cultural evolution of know-how is to determine - for each species examined - whether similar tool use exists in more than one population of the same species, where these populations are culturally unconnected (the so-called "method of local restriction" [84]). Whenever similar tool use shows in such culturally unconnected populations of the same species, this makes it more likely that the tool behaviour is a latent solution. Likewise, if the same tool use appears in one or more populations of one or more closely related species, this is some (more indirect) evidence that it is a latent solution - in all the related species in which it is shown.
Elephants
Asian elephants may use tools in insightful problem solving. A captive male was observed moving a box to a position where it could be stood upon to reach food that had been deliberately hung out of reach.[87][88]
Elephants have also been known to drop large rocks onto an electric fence to either ruin the fence or cut off the electricity.[89]
Cetaceans
A community of Indo-Pacific
There is evidence that both ecological and cultural factors predict which dolphins use sponges as tools. Sponging occurs more frequently in areas with higher distribution of sponges, which tends to occur in deeper water channels.
Indo-Pacific bottlenose dolphins in Shark Bay have also been observed carrying conch shells. In this behaviour, dolphins insert their rostrum into the shell's aperture. Although this behaviour is rare, it appears to be used for foraging. Dolphins appear to use the conch shells to scoop fish from the substrate then carry the shell to retrieve the fish near the surface.[100]
Sea otters
Under each foreleg, the sea otter (Enhydra lutris) has a loose pouch of skin that extends across the chest. In this pouch (preferentially the left side), the animal stores collected food to bring to the surface. Otters are also known to keep rocks in this "pocket" that they use to crack open clams and shellfish.[101] To open hard shells, it may pound its prey with both paws against the rock which it places on its chest. Furthermore, sea otters will use large stones to pry an abalone off its rock; they will hammer the abalone shell with observed rates of 45 blows in 15 seconds or 180 rpm, and do it in two or three dives. Releasing an abalone, which can cling to rock with a force equal to 4,000 times its own body weight, requires multiple dives by the otter.[102] Furthermore, out of the thirteen currently known species of otters, at least 10 demonstrate stone-handling behaviour, suggesting that otters may have a genetic predisposition to manipulate stones.[103]
Other carnivores
Wild
Honey badgers both wild and captive have been filmed manipulating various objects to assist them in making climbs, including making mud balls and stacking them. In 2021, a South African honey badger named Stoeffel repeatedly escaped his enclosure to attack the next door lions. Stoeffel went so far as to build a ramp to get over the wall.[105]
North American badgers (Taxidea taxus) hunt Richardson's ground squirrels (Spermophilus richardsonii). The most common hunting technique is excavation of burrow systems, but plugging of openings into ground-squirrel tunnels accounts for 5–23% of hunting actions. Badgers usually use soil from around the tunnel opening, or soil dragged 30–270 cm from a nearby mound to plug tunnels. The least common (6%), but most novel, form of plugging used by one badger involved movement of 37 objects from distances of 20–105 cm to plug openings into 23 ground-squirrel tunnels on 14 nights.[106]
In 2011, researchers at the Dingo Discovery and Research Centre in Melbourne, Australia, filmed a dingo manipulating a table and using this to get food.[107]
Other mammals
A family of captive Visayan warty pigs have been observed using a flat piece of bark as a digging tool.[110] Horses have also been observed using different tools.[111]
In birds
Tool use is found in at least thirty-three different
Many birds (and other animals) build nests.
Prey-dropping behaviour is seen in many species of birds. Species of crows such as Carrion, Northwestern, American, and New Caledonian crows exhibit this behaviour using different prey.[116][117][118][119][120] Gulls, particularly Kelp, Western, Black-Headed and Sooty gulls are also known to drop mussels from a height as a foraging adaptation.[121][122][123][124] This behaviour is demonstrated by dropping prey from a height onto a hard substrate in order to break the prey's shell open. Several variables such as prey size, substrate type, kleptoparasitism, etc. can influence the behaviour of prey dropping in various species.[116]
Finches
Perhaps the best known and most studied example of an avian tool user is the woodpecker finch (Camarhynchus pallidus) from the Galápagos Islands. If the bird uncovers prey in bark which is inaccessible, the bird then flies off to fetch a cactus spine which it may use in one of three different ways: as a goad to drive out an active insect (without necessarily touching it); as a spear with which to impale a slow-moving larva or similar animal; or as an implement with which to push, bring towards, nudge or otherwise maneuver an inactive insect from a crevice or hole. Tools that do not exactly fit the purpose are worked by the bird and adapted for the function, thus making the finch a "tool maker" as well as a "tool user". Some individuals have been observed to use a different type of tool with novel functional features such as barbed twigs from blackberry bushes, a plant that is not native to the islands. The twigs were first modified by removing side twigs and leaves and then used such that the barbs helped drag prey out of tree crevices.[8]
There is a genetic predisposition for tool use in this species, which is then refined by individual trial-and-error learning during a sensitive phase early in development. This means that, rather than following a stereotypical behavioural pattern, tool use can be modified and adapted by learning.
The importance of tool use by woodpecker finch species differs between vegetation zones. In the arid zone, where food is limited and hard to access, tool use is essential, especially during the dry season. Up to half of the finches' prey is acquired with the help of tools, making them even more routine tool users than chimpanzees. The tools allow them to extract large, nutritious insect larvae from tree holes, making tool use more profitable than other foraging techniques. In contrast, in the humid zone, woodpecker finches rarely use tools, since food availability is high and prey is more easily obtainable. Here, the time and energy costs of tool use would be too high.[8]
There have been reported cases of woodpecker finches brandishing a twig as a weapon.[14]
Corvids
Corvids are a family of birds characterised by relatively large brains, remarkable behavioural plasticity (especially highly innovative foraging behaviour) and well-developed cognitive abilities.[8][125]
Carrion crows
Carrion crows were observed on Eden estuary in Scotland between February and March 1988 to investigate their dropping strategies with mussels. Carrion crows selected larger mussels and dropped them from a height of ~8m onto hard substrate. The height of mussels dropped were lower than what researchers expected, which may be due to difficulty locating prey post dropping as well as trying to prevent kleptoparasitism (stealing of food by other scavengers). Behaviour of prey dropping seen in carrion crows suggest that the size of prey, substrate surfaces, and height drop influence their behaviour. Therefore, it can be inferred that other species may exhibit different behaviour strategies based on their prey, and environment.[120]
Northwestern crows
Different variables such as, prey size, shell breakability, predators, substrate, and height affect the behaviour of prey dropping for different species. For instance, selection of prey may depend on substrate used in that environment.
American crows
American crows are another of several species of birds that possess prey dropping behaviour. When performing the study of prey dropping in American crows, the number of drops to crack a walnut decreased as the height of prey dropped increased and crows had more success when dropping walnuts onto asphalt compared to soil. Prey loss almost always occurred through kleptoparasitism however, there is a lack of evidence that shows kleptoparasitism being directly affected by height of prey dropped.[117]
Caledonian crows
New Caledonian crows (Corvus moneduloides) are perhaps the most studied corvid with respect to tool-use.
In the wild, they have been observed using sticks as tools to extract insects from tree bark.[126][127] The birds poke the insects or larvae until they bite the stick in defence and can then be drawn out. This "larva fishing" is very similar to the "termite fishing" practised by chimpanzees. In the wild, they also manufacture tools from twigs, grass stems or similar plant structures, whereas captive individuals have been observed to use a variety of materials, including feathers and garden wire. Stick tools can either be non-hooked—being more or less straight and requiring only little modification—or hooked. Construction of the more complex hooked tools typically involves choosing a forked twig from which parts are removed and the remaining end is sculpted and sharpened. New Caledonian crows also use pandanus tools, made from barbed leaf edges of screw pines (Pandanus spp.) by precise ripping and cutting although the function of the pandanus tools is not understood.[128]
While young birds in the wild normally learn to make stick tools from elders, a laboratory New Caledonian crow named "Betty" was filmed spontaneously improvising a hooked tool from a wire. It was known that this individual had no prior experience as she had been hand-reared.[129] New Caledonian crows have been observed to use an easily available small tool to get a less easily available longer tool, and then use this to get an otherwise inaccessible longer tool to get food that was out of reach of the shorter tools. One bird, "Sam", spent 110 seconds inspecting the apparatus before completing each of the steps without any mistakes. This is an example of sequential tool use, which represents a higher cognitive function compared to many other forms of tool use and is the first time this has been observed in non-trained animals. Tool use has been observed in a non-foraging context, providing the first report of multi-context tool use in birds. Captive New Caledonian crows have used stick tools to make first contact with objects that were novel and hence potentially dangerous, while other individuals have been observed using a tool when food was within reach but placed next to a model snake. It has been claimed "Their [New Caledonian crow] tool-making skills exceed those of chimpanzees and are more similar to human tool manufacture than those of any other animal."[8]
New Caledonian crows have also been observed performing tool use behaviour that had hitherto not been described in non-human animals. The behaviour is termed "insert-and-transport tool use". This involves the crow inserting a stick into an object and then walking or flying away holding both the tool and object on the tool.[130]
New Caledonian crows also demonstrate prey-dropping behaviour. The first recorded evidence of this species of crow demonstrating prey dropping behaviour on the snail Placostylus fibratus in a 2013 study.[118] New Caledonian crows dropped snails from a particular height onto rocky beds and video recording showed one crow repeating this four times from the same height.[118]
Hawaiian crow
Captive individuals of the critically endangered Hawaiian crow (Corvus hawaiiensis) use tools to extract food from holes drilled in logs. The juveniles exhibit tool use without training or social learning from adults. As 104 of the 109 surviving members of the species were tested, it is believed to be a species-wide ability.[131][132]
Others
Other corvid species, such as rooks (Corvus frugilegus), can also make and use tools in the laboratory, showing a degree of sophistication similar to that of New Caledonian crows.[8] While not confirmed to have used tools in the wild, captive blue jays (Cyanocitta cristata) have been observed using strips of newspaper as tools to obtain food.[133][134]
Various corvids have reached for stones to place in a vessel of water so as to raise the surface level to drink from it or access a floating treat, enacting Aesop's Fable of The Crow and the Pitcher.
A wild
Common ravens (Corvus corax) are one of only a few species who make their own toys. They have been observed breaking off twigs to play with socially.[140] A corvid has been filmed sliding repeatedly down a snow-covered roof while balancing on a lid or tray.[141][142][143] Another incidence of play in birds has been filmed showing a corvid playing with a table tennis ball in partnership with a dog, a rare example of tool use for the purposes of play.[144] Blue jays, like other corvids, are highly curious and are considered intelligent birds. Young blue jays playfully snatch brightly coloured or reflective objects, such as bottle caps or pieces of aluminium foil, and carry them around until they lose interest.
Warblers
The tailorbird (genus Orthotomus) takes a large growing leaf (or two or more small ones) and with its sharp bill pierces holes into opposite edges. It then grasps spider silk, silk from cocoons, or plant fibres with its bill, pulls this "thread" through the two holes, and knots it to prevent it from pulling through (although the use of knots is disputed[145]). This process is repeated several times until the leaf or leaves forms a pouch or cup in which the bird then builds its nest.[14][146] The leaves are sewn together in such a way that the upper surfaces are outwards making the structure difficult to see. The punctures made on the edge of the leaves are minute and do not cause browning of the leaves, further aiding camouflage. The processes used by the tailorbird have been classified as sewing, rivetting, lacing and matting. Once the stitch is made, the fibres fluff out on the outside and in effect they are more like rivets. Sometimes the fibres from one rivet are extended into an adjoining puncture and appear more like sewing. There are many variations in the nest and some may altogether lack the cradle of leaves. It is believed that only the female performs this sewing behaviour.[145] The Latin binomial name of the common tailorbird, Orthotomus sutorius, means "straight-edged" "cobbler" rather than tailor.[147] Some birds of the genus Prinia also practise this sewing and stitching behaviour.[148]
Brown-headed nuthatches
Brown-headed nuthatches (Sitta pusilla) have been observed to methodically use bark pieces to remove other flakes of bark from a tree. The birds insert the bark piece underneath an attached bark scale, using it like a wedge and lever, to expose hiding insects. Occasionally, they reuse the same piece of bark several times and sometimes even fly short distances carrying the bark flake in their beak. The evolutionary origin of this tool use might be related to these birds frequently wedging seeds into cracks in the bark to hammer them open with their beak, which can lead to bark coming off.
Brown-headed nuthatches have used a bark flake to conceal a seed cache.[8]
Crested lark
A crested lark (Galerida cristata) has been photographed apparently holding in its bill a stone chip it was reportedly using to dislodge prey from paving joints.[149]
Parrots
Kea, a highly inquisitive New Zealand mountain parrot, have been filmed stripping twigs and inserting them into gaps in box-like stoat traps to trigger them. Apparently, the kea's only reward is the banging sound of the trap being set off.[150] In a similarly rare example of tool preparation, a captive Tanimbar corella (Cacatua goffiniana) was observed breaking off and "shaping" splinters of wood and small sticks to create rakes that were then used to retrieve otherwise unavailable food items on the other side of the aviary mesh.[151][152] This behaviour has been filmed.
Many owners of household parrots have observed their pets using various tools to scratch various parts of their bodies. These tools include discarded feathers, bottle caps, popsicle sticks, matchsticks, cigarette packets and nuts in their shells.[14]
Hyacinth macaws (Anodorhynchus hyacinthinus) have been repeatedly observed to use tools when breaking open nuts, for example, pieces of wood being used as a wedge. Several birds have wrapped a piece of leaf around a nut to hold it in place. This behaviour is also shown by palm cockatoos (Probosciger aterrimus). It seems that the hyacinth macaw has an innate tendency to use tools during manipulation of nuts, as naïve juveniles tried out a variety of objects in combination with nuts.[8]
Tool use behaviour has been observed in the kea, wherein a bird named Bruce, who has a broken upper beak, wedged pebbles between his tongue and lower mandible and then utilised this arrangement to aid with his preening habits.[153]
Tool use behaviour has been observed in the Tanimbar corella in captivity. It was reported in November 2012 by Professor Alice Auersperg of the University of Vienna, that a cock bird named Figaro was observed spontaneously shaping splinters of wood and small sticks in order to create rakes that were then utilised to extend his reach and retrieve otherwise unavailable food items located upon the other side of his aviary mesh.[151][154]
In July 2013, the results of a joint study involving scientists from
Further research in 2020 by Auersperg's team compared the problem-solving ability of the captive-bred Goffins at the Goffin Lab with wild birds caught in Tanimbar and exposed to the same experimental conditions – in which the birds were placed in an "innovation arena" and presented a series of 20 different tasks (e.g. pressing a button, turning a wheel, pulling out a drawer, removing a twig, overturning a cup, opening a clip, etc.) which they could choose to partake in, in order to obtain a food reward. It was found that while the wild Goffins were less inclined to interact with the test apparatus, those that did solved the presented tasks at a similar rate to the captive-bred birds.[156]
Wild Goffins were also observed shaping sticks of different dimensions in order to create a series of tools which enabled them to eat
Egyptian vultures
When an Egyptian vulture (Neophron percnopterus) encounters a large egg, it takes a stone into its beak and forcefully throws it at the egg until the shell is broken, usually taking a few minutes. This behaviour, first reported in 1966,[158] seems to be largely innate and is displayed by naïve individuals. Its origin could be related to the throwing of eggs; rounded (egg-like) stones are preferred to jagged ones.[159]
In a small population in Bulgaria, Egyptian vultures use twigs to collect sheep wool for padding their nests. Although both twigs and wool can serve as nesting material, this appears to be deliberate tool use. The birds approached bits of discarded wool with a twig in their beak, which was then either used as a rake, to gather the wool into heaps, or to roll up the wool. Wool was collected only after shearing or simulated shearing of sheep had taken place, but not after wool had simply been deposited in sheep enclosures.[160]
Fire-foraging raptors
In Australia the black kite (Milvus migrans), whistling kite (Haliastur sphenurus) and unrelated brown falcon (Falco berigora) are not only attracted to wildfires to source food, but will variously use their beaks or talons to carry burning sticks so as to spread fire, complicating human efforts to contain fires using firebreaks.[161]
Owls
Burrowing owls (Athene cunicularia) frequently collect mammalian dung, which they use as a bait to attract dung beetles, a major item of prey.[162]
Gulls
Gulls have been known to drop mollusc shells on paved and hard surfaces such as roads. Their dropping habits are similar to corvids in the sense that repeated drops allow gulls to have easier access towards their prey. Certain species (e.g. the herring gull) have exhibited tool use behaviour, using pieces of bread as bait to catch goldfish, for example.[18]
Kelp gulls
Kelp gulls are one of the well-known gulls that have displayed prey-dropping.[123] These gulls are known to learn their prey-dropping skills by studying other gulls around them, and are able to refine this behaviour to benefit themselves. They commonly break their prey on hard surfaces, such as rocks, asphalt, and even roofs of houses and cars. Kelp gulls normally drop black mussels, and drop-sites are normally chosen based on how well it would break the prey as well as the amount of kleptoparasites that are in the area, as other gulls may take the opportunity to steal an individual's prey. Dropping behaviour occurs at any time of year but is more prevalent in the winter during low-tide hours, most likely due to having more access to larger mussels. Kelp gulls will fly over 0.5 km to a preferred substrate on which to break their prey. Height from which the prey is dropped will increase after each drop of the prey. Once the prey is dropped, a gull will descend as quickly as possible to recover its prey. This is likely to prevent kleptoparasitism, which is very common in prey-dropping. On average, a kelp gull will descend at an average of 4 m/s in comparison to the prey's fall of 5 m/s, which allows the gull to reach the ground about 0.5 seconds after the prey has landed onto the surface.[123] Adult kelp gulls have a higher success rate of breaking and obtaining their prey while prey dropping than juvenile kelp gulls.[123]
Western gulls
Western gulls are one of the many species of gulls that have been observed to drop their prey on the ground.[122] A study observed that a major factor influencing dropping behaviour in these gulls had to do with the mass and size of the prey being dropped. When performing a study using different sizes of Washington clams, smaller clams were normally pecked at. The larger clams however were dropped unless they were too heavy to carry, usually exceeding 268 grams in weight. Drop behaviour differs between adult and immature western gulls. All adult western gulls that have been studied displayed prey dropping behaviour, and dropped from an average of 118 metres away from where they were originally retrieved. In the study, dropping occurred either over mudflats or a parking lot, which correlated with weight of the clams, which average clam weights were 106.7 g and 134.3 g respectively. Immature gulls meanwhile are much more clumsy with their dropping, and only 55% of juvenile western gulls that were observed displayed this behaviour. Juvenile gulls also did not seem to have a correlation between the weight of the clam and the height the clam was dropped at, though it is noted that the younger gulls seemed to drop their prey at much lower heights than their older peers. This could be evidence of juvenile gulls learning this behaviour through trial and error. The low height at which the clams are dropped may also result in the number of times the younger gulls had to drop their prey. Immature western gulls tend to drop their prey more frequently than the older gulls do, most likely due to inconsistency in drop height as well as the height of the drops. Unlike most birds who drop their prey, western gulls actually seem to prefer softer substrates over larger substrates when dropping their prey, and only seem to drop their prey on hard surfaces if their prey is heavier.[122]
Black-headed gulls
In observations made in Central Europe, a two-year-old black-headed gull was seen taking a small swan mussel about 60 feet up into the air to drop on an asphalt road.[124] It is unknown how successful the gull was seeing as a nearby crow stole the mussel. This was the first time prey-dropping was recorded in this species of gulls. It is likely that this behaviour is not common in this species of gull, as there is no other evidence of black-headed gulls dropping prey. It is more likely that this observation was due to the fact that there was a large group of hood crows during this study, and it may be that the gull observed was mimicking the prey-dropping behaviour of the hood crows nearby. This may be evident seeing as after the gull had dropped the mussel, it made no move to try and grab it for another drop. However, due to the fact that it was not only a single black-headed gull that was observed, but also a young bird, it is possible that successful prey-dropping may occur in other members of this species.[124]
Sooty gulls
In 2009, two sooty gulls near Hamata, Egypt, were seen using prey-dropping behaviour on a strip of coral reef. Unlike other gulls, the gulls only flew up about 6 m and broke molluscs in one drop. All drops were successful.[124]
Herons
The green heron (Butorides virescens) and its sister species the striated heron (Butorides striata) have been recorded using food (bread crusts), insects, leaves, and other small objects as bait to attract fish, which they then capture and eat.[163]
In reptiles
A 2013 paper suggested that American alligators and mugger crocodiles living near bird rookeries used twigs and sticks as bait to catch nesting birds. However, a 2019 study found no support that alligators were displaying sticks as lures, or that the predator was taking the seasonal behavior of the birds into account, as was suggested in the original paper. As of 2023, there is no evidence for tool use in reptiles. [164]
In fish
Several species of
It has been reported that freshwater stingrays use water as a tool by manipulating their bodies to direct a flow of water and extract food trapped amongst plants.[166]
Prior to laying their eggs on a vertical rock face, male and female whitetail major damselfish clean the site by sand-blasting it. The fish pick up sand in their mouths and spit it against the rock face. Then they fan the area with their fins. Finally they remove the sand grains that remain stuck to the rock face by picking them off with their mouths.[167]
Banded acara (Bujurquina vittata), South American cichlids, lay their eggs on a loose leaf. The male and female of a mating pair often "test" leaves before spawning: they pull and lift and turn candidate leaves, possibly trying to select leaves that are easy to move. After spawning, both parents guard the eggs. When disturbed, the parent acara often seize one end of the egg-carrying leaf in their mouth and drag it to deeper and safer locations.[168]
Archerfish are found in the tropical mangrove swamps of India and Australasia. They approach the surface, take aim at insects that sit on plants above the surface, squirt a jet of water at them, and grab them after the insects have been knocked off into the water. The jet of water is formed by the action of the tongue, which presses against a groove in the roof of the mouth. Some archerfish can hit insects up to 1.5 m above the water surface. They use more water, which gives more force to the impact, when aiming at larger prey. Some triggerfish (e.g. Pseudobalistes fuscus) blow water to turn sea urchins over and expose their more vulnerable ventral side.[169] Whether these later examples can be classified as tool use depends on which definition is being followed because there is no intermediate or manipulated object, however, they are examples of highly specialised natural adaptations.
In invertebrates
Cephalopods
At least four
Octopuses deliberately place stones, shells and even bits of broken bottle to form a wall that constricts the aperture to the den, a type of tool use.[171]
In laboratory studies, Octopus mercatoris, a small pygmy species of octopus, has been observed to block its lair using a plastic Lego brick.[12]
Smaller individuals of the common blanket octopus (Tremoctopus violaceus) hold the tentacles of the Portuguese man o' war, to whose poison they are immune, both as protection and as a method of capturing prey.[172]
Insects
Ants of the species Dorymyrmex bicolor pick up stones and other small objects with their mandibles and drop them down the vertical entrances of rival colonies, allowing workers to forage for food without competition.[173]
Several species of ant are known to use substrate debris such as mud and leaves to transport water to their nest. A study in 2017 reported that when two species of Aphaenogaster ant are offered natural and artificial objects as tools for this activity, they choose items with a good soaking capacity. The ants develop a preference for artificial tools that cannot be found in their natural environment, indicating plasticity in their tool-use behaviour.[174]
Hunting wasps of the genus
Some species of crickets construct acoustic baffles from the leaves of plants to amplify sounds they make for communication during mating.[176] It was in 1975 that scientists first observed Oecanthus burmeisteri and two other species of South African chirping crickets doing this.[177]
Insects can also learn to use tools. A study in 2017 showed that bumblebees of the species Bombus terrestris learned to move a small wooden ball to a goal for a sucrose reward.[178]
See also
- Animal cognition
- Animal-computer interaction
- Bird intelligence
- Cephalopod intelligence
- Cetacean intelligence
- Elephant intelligence
- Embodied cognition
- Fish intelligence
- Structures built by animals
- Hermit crab (shell, anemone)
- Cow Tools, a cartoon which attempted to parody this topic
- Primate archaeology
- Zoopharmacognosy (medicinal plant use by animals)
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Further reading
- Robert W. Shumaker; Kristina R. Walkup; Benjamin B. Beck (2011). Animal Tool Behavior: The Use and Manufacture of Tools by Animals. The Johns Hopkins University Press.
- Michael Henry Hansell (2005). Animal architecture. Oxford University Press. p. 1. ISBN 978-0-19-850752-9.
External links
- Chimpanzee making and using a termite "fishing rod"
- Chimpanzee using tool to break into beehive to get honey
- Crow making a tool by bending wire to snag food
- Various tool use by birds
- Fish using an anvil to break open prey
- Dolphin using a marine sponge to protect its rostrum
- Mandrill using a tool to clean under its nails
- New Caledonian crows picking up an object with a tool and transporting both