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Briefly about tool behaviour in animals






 

There are several detailed monographs about tool using in animals. Among them, Beck (1980) systematises the great body of data on how tool use is distributed within a wide variety of species. Goodall (1970, 1986) was first to summarise long term observations on tool using in chimpanzees, and McGrew in his books (1992, 2004) has given encyclopaedic description of tool using as a basic element of “culture” in our closest relatives. Here I place a brief review of tool using in wild and captured animals which act freely not being forced by researchers to solve any special problems with the use of tools.

Concepts and definitions. When considering tool behaviour, tools must be clearly distinguished from artefacts. Artefacts are common in the animal kingdom: beehives and beaver lodges are among the finest examples-and they are made by some creatures quite low in the evolutionary scale (such as the caddie fly larva that makes cases and nets). Tools are distinct from artefacts because they can be used to make other objects or to facilitate activities such as resource extraction. They are not by themselves of immediate and direct use. There are two distinctive tool behaviours in animals, namely, tool use and tool manufacture.

The generally accepted definition of animal tool use is that the animal is using an unattached environmental object to alter the form, position or condition of another object or organism, when the user holds or carries the tool during its use and is responsible for a proper and effective orientation of the tool (Beck, 1980). In terms of levels of sophistication, animals may or may not choose morphologically and functionally variable tools, showing selectivity amongst them so that a functionally appropriate tool is chosen for a task (Parker and Gibson, 1979; Tomasello and Call, 1997).

Tool manufacture includes four modes of tool behaviour. The simplest and most common is severing the fixed attachment between one environmental object and another (or the substrate) so that the first object can be used as a tool. This mode is termed detach. Examples are breaking a branch from a tree for use as a club or uprooting a sapling which is then brandished. The second mode, subtraction, is removing an object or objects from another unattached object so that the latter can serve more usefully as a tool. For example, a chimpanzee is subtracting when it removes leaves from a twig when the twig is to be used for termite or ant fishing. If, however, the ape removes the leaves so that the leaves can be used for wiping, it is detaching. The third modes are addition or combination in which two or more objects are connected to produce an adequate tool. An example is a chimpanzee connecting two short sticks to produce one of sufficient length to reach food. The last mode of tool manufacture is reshaping. This involves fundamental restructuring of material to provide a functional tool. Examples include chimpanzees crumpling leaves to increase their absorbency as a sponge or unrolling a coil of wire to produce a straight reaching tool (Beck, 1980; Whiten et al., 1999; McGrew, 2004). Recently came the first report of customary use of tool-sets - two or more different types of tool used in sequence to achieve a single goal - by a community of wild chimpanzees in the Congo Basin (Sanz et al., 2004). Chimpanzees tap termites from their mounds firstly perforating with heavy sticks to punch holes in termite mounds. Having gained access, they use a lighter stick known as a fishing tool to extract termites. It is worth to note that apes select specific materials for their puncturing tools, often gathering the sticks far from the termite nests and transporting them to the nests, where the chimps modified their selected sticks by stripping leaves and shortening them to a uniform length.

Let us survey how these modes are distributed in different species, from elephants to ants. As it has been already noted, Beck collected in his (1980) book a huge data about animals that were observed as tool users. Among them such unexpected creatures related to tool use as rodents, antelopes, ant lions, and sea anemones. Here we will consider only usual and frequently cited examples of animal’s tool behaviour in order to create the necessary prerequisites for the analysis of instrumental problem solving as an essential part of studying animal intelligence.

A club of tool users: description of phenomena and related problems. Asian elephants Elephas maximus and African elephants Loxidonta africana throw sticks, logs and stones at other animals and use sticks to scratch parts of the body; they wipe blood by tufts of grass and cork up wounds with them (Douglas-Hamilton and Douglas-Hamilton, 1975; Chevalier-Skolnikoff and Liska, 1993). Elephants definitely express tool manufacture such as subtraction modifying branches for fly switching. A great storyteller Rudyard Kipling alluded to elephants fly switching in the Chapter “The Elephant’s Child” in his 1902 “Just So Stories”. The elephant’s child, having acquired a new trunk (courtesy of the crocodile), starts for home and Kipling notes that, when flies bit him he broke off the branch of a tree and used it as a fly-whisk. Indeed, elephant’s prehensile trunk equipped with the special “finger” is capable of some of the same delicate manipulative movements performed by primates with their fingers. Use of branches for fly switching is a common form of tool use in elephants. Hart and co-authors (2001) presented to 13 Asian elephants maintained under a naturalistic system, branches that were too long or bushy to be effectively used as switches. Eight of these elephants modified the branches make them smaller and switched with the altered branch. There were different styles of modification of the branches, the most common of which was holding the main stem with the front foot and pulling off a side branch or the distal end with the trunk.

Sea otters provide one of the best-documented forms of tool use in wild animals. Fisher (1939) first described tool use in California sea otters Enhydra lutris nereis that hammered small molluscs on rocks placed on the animal’s chests. Hall and Schaller (1964) made detailed observations of tool behaviour of these animals which have no match among other species in the sophisticated use of stones as tools. The otter surfaces with a single mussel and a stone, rolls so that it is floating on its dorsum with the stone balanced on its ventrum, and then immediately begin to pound the flat side of the mussel against the stone. The mussel is held with both forefeet. The otters pound the mussels in series of forceful blows at the rate of 2 per second. The longest feeding sequence by one otter involving tools lasted 86 minutes; during which 54 mussels were consumed and 2 237 bowls were struck. Stones would sometimes be transported during subsequent dives and reused; one was used 12 consecutive times. There are many variations of tool behavioural patterns in sea otters. Sea urchins, crabs and lobsters are pounded on stones. Sea otters can also open clams by pounding them against another clam shell balanced on the ventrum. Houk and Geibel (1974) made observations of sea otters hammering an abalone from the substrate with a stone at a depth of 10 meters. An otter located an abalone in a rocky crevice, picked up a stone, and began to strike the abalone. The otter worked for 88 seconds and three times surfaced to breathe returning with the same rock. Indeed, sea otters offer an opportunity for further study of tool use.

Overwhelming majority of reports of tool behaviour in wild animals concern primates. Relatively simple behaviours such as dropping or throwing objects (branches, twigs, stones, excreta) toward intruders have been described by many authors in Capuchin monkeys, howler monkeys, spider monkeys, squirrel monkeys, woolly monkeys, and some other species (see: Beck, 1980, for a review). However, it takes many efforts to observe regular displays of complex tool behaviour in wild animals. Recently the regular cracking of palm tree nuts with the aid of two stones (“hammer” and “anvil”) have been revealed in Tufted Capuchin monkeys in the Ecological Park of Sao Paolo (Ottoni and Mannu, 2001). A similar style of tool use by Japanese macaques had been monitored for 20 years (Huffman, Nishie, 2001). Vervet monkeys Cecopithecus aethiops use leaves to sponge up water in tree hollows (Hauser, 1988).

Chimpanzees are well established as the most proficient tool users and makers among non-human primates. At the beginning of 20-th century Ladygina - Koths (1923) and Kö hler (1925) attracted attention of scientists to skilful manipulations with objects by apes. The animals used sharp sticks and wires to reach insects in cervices, poles to vault for a suspended banana, twigs as levers to open lids. Apes used a great variety of objects for comforting themselves. They scratched their skin by twigs, stones, and broken pieces of pottery, brushed their nails by sharp sticks and ears by stranded papers, wrapped their hands in paper and leaves when needed to operate with horny objects, and used leaves, sheets of paper and cloth to wipe themselves. Chimpanzees enjoyed advantages of tool use taunting other animals. For example, they called chickens throwing pieces of bread and prodded them with sticks or wires.

First scientific naturalistic study on tool use by wild chimpanzees was conducted by Nissen (1931). Since 1950-th, new observations have appeared in the primatological journals (see: Goodall, 1986 and McGrew, 1992, 2004, for reviews). A systematic synthesis by Whiten and colleagues (Whiten et al., 1999) describes various habits of chimpanzees including styles of the tool use at seven field sites in Africa. We will consider “cultural” aspects of these data in Part VIII. Here it is important to note that the authors described a complete set of tool behaviours such as pounding actions, ant- and termite fishing, nut hammering, absorbing water and honey by chewed leaves, throwing twigs and stones, and so on.

Detailed observations on each particular type of tool use showed that chimpanzees use brains and not brawn to exploit resources ignored by their sympatric competitors such as, say, baboons and gorillas lacking instrumental technology (McGrew, 2001). For example, McGrew (1974) described in details the so-called ant-dipping, that is, tool use by wild chimpanzees upon driver ants. To reach ants, a chimpanzee dips them with the use of shaped branches from rocks, fallen logs or other raised positions in order to avoid ants’ attacks. To make tools, a chimpanzee breaks off a branch of living woody vegetation, and then pulls off leaves. If the tool becomes damaged or coated with soil during the use, the ape may further modify it by biting off worn segments. The chimpanzee is skilful enough to catch ants momentarily in mass that is about the size of a hen’s egg and contains about 300 ants which then are chewed and swallowed. Chimpanzees are the most intelligent insectivores (Fig. VI-2). Bonobos, gorillas and orang-utans may eat many insects, but without instrumental technology and thus with much more efforts and downtime.

For brevity, we have just considered only one from the great number of examples of tool manufacture in anthropoids. It is worth to note that styles of life and technology greatly vary in different local populations. For instance, orang-utans in captivity often use tools, but no one before van Schaik and his colleagues (1999, 2003) had observed this behaviour in wild populations. Living high in the trees of the flooded forest in the north-west corner of Sumatra, members of a local population with high density of orang-utans locate pulpy fruits, of which their favourite is locally called " puwin." Inside this fruit lies a rich source of protein and lipids; outside are tiny hairs that researchers describe from experience as feeling like " Plexiglas needles, " capable of delivering a painful jab. By sliding a thin stick into a crack in the fruit, orang-utans can get the seeds out without having to handle the prickly husk.

In contrast to information from other great apes, which mostly show tool use in the context of food extraction, recent observations of Breuer et al. (2005) show that in gorillas other factors such as habitat type can stimulate the use of tools. The researchers first observed an adult female gorilla using a branch as a walking stick to test water deepness and to aid in her attempt to cross a pool of water at Mbeli Bai, a swampy forest clearing in northern Congo. In the second case they saw another adult female using a detached trunk from a small shrub as a stabilizer during food processing. She then used the trunk as a self-made bridge to cross a deep patch of swamp. There is the intriguing possibility, as the authors give this, that using branches to test water depth or as bridges is a more common adaptation to this particular habitat. These observations show that other but obtaining food resources functional demands may also stimulate tool use, at least in apes.

Another group of organisms that seem to be obvious candidates for investigating the cognitive abilities related to tool use are birds. Although there are only a few bird species for which habitual use of tools is known, at least in two species - New Caledonian Crows and woodpecker finches - skilfulness and flexibility in tool manufacturing can be considered close to that of primates.

Before considering sophisticated tool usage in these two species, I place here several examples of tool behaviour in other birds.

It is known that Egyptian vultures, Neophron percnopterus, drop stones on ostrich eggs (van Lawick-Goodall and van Lawick, 1966). With other bird species that use stones for breaking eggs, black breasted buzzard Hamirostra melanosternon (see: Aumann, 1990) and Egyptian vultures belong to a narrow section of creatures pretending for tool selectivity. Thouless et al. (1989) tested N. percnopterus providing them with models of ostrich eggs and a range of stone sizes. The authors showed that vultures strongly preferred 46-g stones. In similar tests H. melanosternon preferred 40-g stones (Aumann, 1990).

Green-backed herons, Butorides striatus, obtain bait as diverse as live insects, berries, twigs, and discarded crackers, and cast them on the waters. They then crouch and wait for the curious or hungry fish that comes to inspect the lure. The birds have even been observed carefully trimming oversized twigs to the proper dimensions (Walsh et al., 1985). However no studies have compared how well herons would do if they did not fish in this manner. Such estimation recently has been done on “land fishers”, burrowing owls Athene cunicularia (Levey et al., 2004). Their underground nests and surrounding areas are carpeted with the stinky stuff. Observations showed that owls deliberately use mammal dung as tools to reel in a meal and in the process substantially increase the number of dung beetles they eat. In 4-day tests with owls at 10 burrows, researchers found that taking the dung away from the burrows' entrances left the owls with few beetles in their diet. Owls with a refurbished cow-dung decor, however, averaged ten times as many beetle meals during the test.

Recent studies on cognitive abilities associated with tool use in birds revealed remarkable data on flexibility in tool manufacturing in New Caledonian crows and woodpecker finches. These are still the only two well studied examples of tool modification found among birds. In contrast to context-specific stereotyped tool behaviour of many other bird species, New Caledonian crows and woodpecker finches are flexible in their use of tools.

Tool behaviour of New Caledonian crows, Corvus moneduliodes, has recently been used as the motif of a postal stamp from New Caledonia. These birds make and use at least three forms of tools to aid prey capture. Almost everything known about their tool use in the wild is from the work of Hunt and (Hunt, 1996, 2000) and Hunt and Gray (2003, 2004). Crow’s tools include hooks cut from pandanus leaves, stick –type tools made from tree twigs, fern stolons, bamboo stems, tree leaf midribs, and thorny vines. To craft a hook from tree twigs, crows detach secondary twigs from the primary one by nipping at the joint with their beaks, leaving a piece of the primary twig to form a hook. After a twig is detached, crows remove leaves and bark, and have even been observed sculpting the shape of the hook with their beak. The crows carried tools with them as they flew to feeding areas, where they used hooked and narrow-tipped tools to fish out insects from hard-to-get spots.

The Galapagos finch Cactospiza pallida is known to use a cactus (prickly pear) spike to poke out insects embedded in the branches or trunks of trees. Where there are no cacti, Cactospiza breaks off a short stiff twig from a tree. Woodpecker finches even modify their tools: they shorten twigs or break off side twigs that would prevent insertion into holes (Eibl-Eibesfeldt, 1961b; Millikan and Bowman, 1967). These birds spend more time using tools and acquire more food with them than do chimpanzees. Strong ecological correlates have been revealed related to their tool behaviours. In the arid zone during the dry season, when prey is hardly available, finches spend half their foraging time using tools and obtain 50% of their prey this way, whereas in the humid zone birds of the same species rarely use tools (Tebbich et al., 2002). Experimental studies have demonstrated that trial-and-error learning is involved in the acquisition of tool use in young woodpecker finches (Tebbich et al., 2001).

It is amusing that from many species only New Caledonian Crows display such a high level of complexity of tool-related skills as manufacturing tools in a multi-step fashion, or by fine crafting (Kacelnik et al., 2004). The crafting of tools in this species involves (i) selection of appropriate raw material; (ii) preparatory trimming and (iii) three-dimension sculpturing (Hunt and Gray, 2004). Chimpanzees and orang-utans use crumpled leaves as sponges which could be regarded as “re-shaping” and all other known animal tool manufacture involves nothing more complex than detaching or subtracting objects from each other.

The second important thing is that the two most “engineering gifted” species, namely, New Caledonian Crows (Hunt and Gray, 2004) and Chimpanzees (see: McGrew, Marchant and Nishida, eds., 1996) are the only non-humans in which populations show routine tool use (Kacelnik et al., 2004). As it has been noted before, woodpecker finches (Grant and Grant, 2002; Tebbich et al., 2002) and orang-utans (van Schaik et al., 2003) show high frequencies of tool use in some populations, but there are others that never use tools. In all other animals - including sea otters operating with stones in very amazing style - there is either insufficient data to access tool use frequency or tool use is known to be absent in many populations.

At the same time, even being the most profiling tool users, both species display a high degree of genetic adaptations involves in ontogenetic shaping of tool behaviour. Using hand-raised juvenile New Caledonian Crows, Kenward et al. (2005) showed that chicks spontaneously manufacture and use tools, without any contact with adults of their species or any prior demonstration by humans. Similar results were obtained by Firsov (1977) in his experiments with artificially raised chimpanzees that manipulated with many things, used and manufactured tools and built nests for sleeping. Spontaneous tool use has also been recorded in woodpecker finches that were raised lacking contacts with tool using adults (Tebbich et al., 2001).

It is thus a very intriguing problem whether complex tool behaviour in animals should be associated with a high degree of cognitive abilities or with strong genetic adaptation. If both domains are responsible for this type of behaviour, are they distinguishable? We will be trying to find an answer, at least partly, further in this Chapter and in the next paragraph and in Part VII.

 


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