Tool Use and Tool Making

The aye-aye (Daubentonia madagascariensis), a primate endemic to Madagascar, has an unusually long middle finger used to extract insect larvae from trees and fruit pulp. The absence of species that exploit these resources (e.g., there are no woodpeckers in Madagascar), combined with appropriate genetic variability for digit length, led to the evolution of an elongated middle finger. In some species, evolution has favored an alternative solution. Rather than lengthening a finger (as in the aye-aye) or shaping a beak (as in the woodpecker), some species evolved an ability to use tools to exploit food resources (Figure 8.6). Tool use requires using an object to access or protect a resource. Traditionally thought to be a restricted behavioral capacity, tool use is present in a variety of species (Shumaker, Walkup, & Beck, 2011). Here are some examples of tool use.

• Some solitary digger wasps of the genus Ammophila store eggs and paralyzed prey (to be used as food by emerging larvae) in a burrow. The wasp then selects a stone of the appropriate size and transports it to the burrow’s entrance where it is used to seal the hole.

Figure 8.6 Top left: A chimpanzee (Pan troglodytes') is using two stones, one as a hammer and the other as an anvil, to crack a nut. Top right: A New Caledonian crow (Corvus moneduloides) using a stick to extract insect larvae from a tree. Bottom left: An otter (Enhydra lutris) using a stone to break a clam. Bottom right: An Egyptian vulture (Neophron percnopterus) using a stone to break an egg.

Source: Top left: Photograph courtesy of Tetsuro Matsuzawa. Top right: From Rutledge and Hunt, (2004), reproduced with permission from Elsevier. Bottom left: Photo from Creative Commons, https://search.creativecommons.org, by Peter Kaminski, license CC BY 2.0. Bottom right: Photo from Creative Commons, https://search.creativecommons, org, by Maurice Koop, license CC BY-ND 2.0.

• • Several species of wrasses (fish of the family Labridae) have been observed to hold a clam in their mouth and then forcefully throw it against a rock (used as an anvil) until the shell cracked.
• • In the Galapagos Islands, where there are also no native woodpeckers, the woodpecker finch Cactospiza pallida uses cactus spines to poke into insect burrows in trees.
• • Egyptian vultures (Neophron percnopterus) throw stones at eggs, while the African banded mongoose (Mungos /imago) throws the egg onto a hard stone to break it.
• • The sea otter (Enhydra lutris) forages for mussels and bivalves on the sea floor and surfaces with its prey and a flat stone. Floating on its back, the otter strikes the mussel against a stone held on its chest and functioning as an anvil, until it can crash the shell with its teeth.

New Caledonian crows (Corvus moneduloides) not only use tools, but they also manufacture tools. Crows cut twigs and twist them into hook-shaped tools to retrieve insect larvae, a behavior that has been observed both in the wild and in the laboratory (Rutz & St Clair, 2012). In tool making, an object is selected and modified such that it can be later used to obtain a specific resource.

Familiar examples of tool making are found among primates. Primate tool behavior is facilitated by manual dexterity, visual acuity, and a propensity and motivation to manipulate objects. Field observations show that chimpanzees use a wide variety of tools to obtain food. They use stones and wood pieces as hammer and anvil to crack hard nuts, leaves as sponges to absorb water from tree holes, and carefully manufactured twigs and sticks to collect termites from their nests (Shumaker, Walkup, & Beck, 2011).

A similar tool kit has been described in capuchin monkeys (Cebus paella). Laboratory observations show that capuchin monkeys can manufacture sticks from tree branches to dip into corn syrup through holes in a specially designed apparatus. Monkeys also rapidly learn to use a variety of objects as sponges (paper towels, leaves, etc.) to absorb fruit juice from a source that was actually direcdy accessible (Westergaard & Fragaszy, 1987). Whereas it is obvious that these tool users display similar behavioral capacities and achieve analogous outcomes, the development of such behavior shows important species differences. In one experiment, capuchin monkeys (Cebus apelld), chimpanzees (Pan troglodytes), bonobos (Pan paniscus), and an orangutan (Pongo pygmaeus) rapidly learned to insert a stick into a clear tube to remove a piece of food placed inside the tube (Visalberghi, Fragaszy, & Savage-Rumbaugh, 1995). However, differences between the capuchin monkeys and the apes emerged when three sticks were bundled together so that they would not fit inside the tube. Capuchin monkeys solved this problem by trial and error, attempting first, unsuccessfully, to insert the bundle into the tube. Prior training with the stick interfered with the resolution of the new problem—negative transfer. By contrast, apes solved this problem without attempting to insert the bundle into the tube—positive transfer. In apes, prior training with a single stick facilitated the resolution of the new problem with the bundled sticks (see Chapters 5 and 7 for additional studies of transfer of learning in primates).

Apes also show their planning capacities in the context of tool use (Byrne, Sanz, & Morgan, 2013). Planning implies the selection of a particular tool, which provides no immediate advantage or reward, to be used in the future for a specific task. In one experiment (Mulcahy & Call, 2006a), bonobos and orangutans received training to use a tool to have access to a piece of food. Once they had mastered the problem, they were allowed 5 min in a room with two suitable and six unsuitable tools. Then, they were moved to a waiting room for 1 h, and finally they had access to the baited apparatus where they could obtain the food by using the suitable tool. After several trials, both bonobos and orangutans learned to transport the appropriate tool to the waiting room and then use the tool to obtain food. In an additional test, one bonobo and one orangutan showed tool transport when they had to wait overnight for 14 h before they could use the tool to obtain food. These apes appear to be planning for the future use of a tool.