Tool use by non-humans is a phenomenon in which a non-human animal uses any kind of tool in order to achieve a goal such as acquiring food and water, grooming, combat, defence, communication, recreation or construction. Originally thought to be a skill possessed only by humans, some tool use requires a sophisticated level of cognition. There is considerable discussion about the definition of what constitutes a tool and therefore which behaviours can be considered true examples of tool use. A wide range of animals, including mammals, birds, fish, cephalopods, and insects, are considered to use tools.

Primates are well known for using tools for hunting or gathering food and water, cover for rain, and self-defence. Chimpanzees have often been the object of study in regard to their usage of tools, most famously by Jane Goodall, since these animals are frequently kept in captivity and are closely related to humans. Wild tool use in other primates, especially among apes and monkeys, is considered relatively common, though its full extent remains poorly documented, as many primates in the wild are mainly only observed distantly or briefly when in their natural environments and living without human influence. Some novel tool-use by primates may arise in a localised or isolated manner within certain unique primate cultures, being transmitted and practised among socially connected primates through cultural learning. Many famous researchers, such as Charles Darwin in his 1871 book The Descent of Man, have mentioned tool use in monkeys (such as baboons).

Among other mammals, both wild and captive elephants are known to create tools using their trunks and feet, mainly for swatting flies, scratching, plugging up waterholes that they have dug (to close them up again so the water does not evaporate), and reaching food that is out of reach. In addition to primates and elephants, many other social mammals particularly have been observed engaging in tool use. A group of dolphins in Shark Bay uses sea sponges to protect their beaks while foraging. Sea otters will use rocks or other hard objects to dislodge food (such as abalone) and break open shellfish. Many or most mammals of the order Carnivora have been observed using tools, often to trap prey or break open the shells of prey, as well as for scratching and problem-solving.

Corvids (such as crows, ravens and rooks) are well known for their large brains (among birds) and tool use. New Caledonian crows are among the only animals that create their own tools. They mainly manufacture probes out of twigs and wood (and sometimes metal wire) to catch or impale larvae. Tool use in some birds may be best exemplified in nest intricacy. Tailorbirds manufacture 'pouches' to make their nests in. Some birds, such as weaver birds, build complex nests utilising a diverse array of objects and materials, many of which are specifically chosen by certain birds for their unique qualities. Woodpecker finches insert twigs into trees in order to catch or impale larvae. Parrots may use tools to wedge nuts so that they can crack open the outer shell of nuts without launching away the inner contents. Some birds take advantage of human activity, such as carrion crows in Japan, which drop nuts in front of cars to crack them open.

Several species of fish use tools to hunt and crack open shellfish, extract food that is out of reach, or clear an area for nesting. Among cephalopods (and perhaps uniquely or to an extent unobserved among invertebrates), octopuses are known to utilise tools relatively frequently, such as gathering coconut shells to create a shelter or using rocks to create barriers.

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 ... 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 weaver ants using conspecifics to glue leaves together. These have been termed "social tools".^[11]

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 shrikes (Laniidae) is well known.^[15] Several other birds may use spines or forked sticks to anchor a carcass while they flay it with the bill. It has been concluded that "This is an example of a fixed device which serves as an extension of the body, in this case, talons" and is thus a true form of tool use. On the other hand, the use of fixed skewers may not be true tool-use because the thorn (or other pointed objects) is not manipulated by the bird.^[14] Leopards perform a similar behaviour by dragging carcasses up trees and caching them in the forks of branches.^[16]

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 learning and cognition. For some animals, tool use is largely instinctive and inflexible. For example, the woodpecker finch of the Galápagos Islands use twigs or spines as an essential and regular part of its foraging behaviour, but these behaviours are often quite inflexible and are not applied effectively in different situations. The mechanisms driving other tool use, e.g. chimpanzee tool-use, are still debated. Whilst some may argue that behaviours such as using twigs to "fish" for termites, may be developed by watching others use tools and may even be a true example of animal teaching, studies with captive chimpanzees have found that many of these species-typical behaviours (including termite fishing) are individually learnt by each chimpanzee.^[22][23] Tools may even be used in solving puzzles in which the animal appears to experience a "Eureka moment".

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.^[27] In the wild, mandrills have been observed to clean their ears with modified tools. Scientists filmed a large male mandrill at Chester Zoo (UK) stripping down a twig, apparently to make it narrower, and then using the modified stick to scrape dirt from underneath his toenails.^[28] Captive gorillas have made a variety of tools.^[29]

Chimpanzees and bonobos

Chimpanzees are sophisticated tool users with behaviours including cracking nuts with stone tools and fishing for ants or termites with sticks. These chimpanzees not only use these sticks to fish out their meal, but they in fact build their own 'tool kits' to do so, as observed in the Republic of Congo. They first use a smaller stick to break open the termite or ant mound, then use a large stick to make holes in the prey's colony, and then insert a 'fishing probe' into the hole and pull out all the termites or ants that have gathered on the stick.^[30] There are more limited reports of the closely related bonobo (Pan paniscus) using tools in the wild; it has been claimed they rarely use tools in the wild although they use tools as readily as chimpanzees when in captivity,^[31] It has been reported that females of both chimpanzees and bonobos use tools more avidly than males.^[32] Leonid Firsov reported a case when two female chimpanzees had the keys to their cage accidentally left at least 2.7 meters (9 feet) away from it, and managed to use objects at hand as improvised tools to retrieve them and get out.^[33] Wild chimpanzees predominantly use tools in the context of food acquisition, while wild bonobos appear to use tools mainly for personal care (cleaning, protection from rain) and social purposes. Wild bonobos have been observed using leaves as cover for rain, or the use of branches in social displays.^[31]

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 colobus monkeys with the help of small sticks, after opening the ends of the bones with their teeth.^[39] A juvenile female was observed to eat small parts of the brain of an intact skull that she could not break open by inserting a small stick through the foramen magnum. On another occasion, an adult female used three sticks to clean the orbits of a colobus monkey skull after she had just eaten the eyes.^[25]

A bonobo fishing for termites

In Gombe National Park in 1960, Jane Goodall observed a chimpanzee, David Greybeard, poking pieces of grass into a termite mound and then raising the grass to his mouth. After he left, Goodall approached the mound and repeated the behaviour because she was unsure what David was doing. She found that the termites bit onto the grass with their jaws. David had been using the grass as a tool to "fish" or "dip" for termites.^[24] Soon after this initial discovery of tool use, Goodall observed David and other chimpanzees picking up leafy twigs, stripping off the leaves, and using the stems to fish for insects. This modification of a leafy twig into a tool was a major discovery: previously, scientists thought that only humans made and used tools, and that this was what separated humans from other animals.^[24]

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 Tai National Park only sometimes use tools, whereas Gombe chimpanzees rely almost exclusively on tools for their intake of driver ants. This may be due to difference in the rewards gained by tool use: Gombe chimpanzees collect 760 ants/min compared to 180 ants/min for the Tai chimpanzees.^[25]

Some chimpanzees use tools to hunt large bees (Xylocopa sp.) which make nests in dead branches on the ground or in trees. To get to the grubs and the honey, the chimpanzee first tests for the presence of adults by probing the nest entrance with a stick. If present, adult bees block the entrance with their abdomens, ready to sting. The chimpanzee then disables them with the stick to make them fall out and eats them rapidly. Afterwards, the chimpanzee opens the branch with its teeth to obtain the grubs and the honey.^[25]

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