Rooks Use Stones to Raise the Water Level to Reach a Floating Worm

In Aesop's fable “The Crow and the Pitcher,” a thirsty crow uses stones to raise the level of water in a pitcher and quench its thirst. A number of corvids have been found to use tools in the wild [1], [2], [3] and [4], and New Caledonian crows appear to understand the functional properties of tools and solve complex physical problems via causal and analogical reasoning [5], [6], [7], [8], [9], [10] and [11]. The rook, another member of the corvid family that does not appear to use tools in the wild, also appears able to solve non-tool-related problems via similar reasoning [12]. Here, we present evidence that captive rooks are also able to solve a complex problem by using tools. We presented four captive rooks with a problem analogous to Aesop's fable: raising the level of water so that a floating worm moved into reach. All four subjects solved the problem with an appreciation of precisely how many stones were needed. Three subjects also rapidly learned to use large stones over small ones, and that sawdust cannot be manipulated in the same manner as water. This behavior demonstrates a flexible ability to use tools, a finding with implications for the evolution of tool use and cognition in animals.