Tool use and animals: How birds are chipping away at its definition


Tool use among animals is nothing new; the definition has been ever evolving as new examples are brought forth for examination. Eleven variations now exist of the original definition, with the most current stated,

…(as the) external employment of an unattached or manipulatable 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.

by Dr. Robert Shumaker, in his book, Animal Tool Behavior: The Use and Manufacture of Tools by Animals. Using these terms, a segue is offered for animals classified as “borderline” tool users, to be re-considered for categorization as tool users. Such would be the case of the Great Spotted Woodpecker.

In October, 2014, Animal Cognition released the publication, “Manipulation of Walnuts to Facilitate Opening by the Great Spotted Woodpecker (Picoides major): Is it Tool Use?”, conducted by researchers Xianfeng Yi, Michael A. Steele, and Zhen Shen. Their study was held in the Heilongjang province of northeast China, and documented the harvesting of walnuts produced by the Manchurian walnut tree using what appears to be tool use behavior by the Great Spotted Woodpecker.

To summarize their experiment, Yi, Steele, and Shen built five platforms, each stocked with 20 walnuts, individually equipped with lightweight radio transmitters. Various members of P. major were then seen to retrieve a given walnut and fly off to open them at a later time. Once relocated, researchers found an overwhelming majority of walnuts, 98%, were positioned with a similar orientation. It was such that the walnuts’ weakest point of entry, known as the hilum, faced the bird directly for pecking and was wedged between adjoining branches of a tree. Intrigued, the researchers decided to offer an additional 60 walnuts. But rather than loosely offer them in a pile for birds to retrieve, the researchers wedged the walnuts between adjoining branches.

The orientations of the hilum was, both directed vertically and flush with the branches, horizontally and flush with the ground, or diagonally in an alternative direction. The purpose of this was to see if the birds could recognize an improper orientation and rearrange the walnuts to open them more easily. Results revealed, birds recovered 27 of the 60 walnuts, and successfully, reoriented 90% of those horizontally so that the hilum would face the bird directly. Meaning, the birds were able to recognize an improper orientation.

It bears mentioning, classic tool use behavior in avian species is rare. A few examples include the New Caledonian Crow and Woodpecker Finch; both of which use twigs and like objects as an extension of their short bills to retrieve food. Other examples include the Green heron, which baits its prey using objects set upon the surface of water to lure fish, and the Egyptian Vulture which is capable of cracking eggs for food by dropping rocks onto them, and also by rolling twigs in wool to use as an insulator when building its nests. In each of these cases, the birds are physically using and/or altering an unattached object for their personal benefit. With a case such as the Great Spotted Woodpecker, the birds require a tree’s stability to open the walnut. Because they never move or alter the tree’s position, this behavior is classified as borderline tool use. However, researchers Yi, Steele, and Shen seem to believe they can build an argument for the science community to reexamine classifying these birds as tool users.

At the core of their argument is the idea that, “the woodpeckers are definitely manipulating the nuts in an orientation that is required for the tool to be effective.” It is no longer simply wedging an object so that it doesn’t move, but it is knowingly repositioning the walnut so that its weakest point of entry faces the bird directly. This repeated behavior shows a higher level of cognitive reasoning skills, which seems to be the shared link between tool users of different species. It suggests to researchers that perhaps this birds’ neurological development may be different when compared to similar species. Such is the interest of these researchers for future study.

Animals are dispelling and challenging our preconceived notions. Thankfully, people are beginning to recognize the change. This simple act speaks volumes for the future development of Ecology and like disciplines. It also tells us, the argument of tool use classification continues to remain debatable.

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