Spontaneous construction of Chinese boxes by Degus (Octodon degu):: A rudiment of recursive intelligence?

The ability to hierarchically combine multiple objects to construct a self-embedded structure is assumed to be unique to primates and parrots. However, we observed that Degus, a species of rodents, spontaneously constructed this structure while they were being trained for an unrelated vocal operant task. With a large dust-bath bowl, a medium sized food cup, and a small toy ball, they built a triplet Chinese boxes. The strategy by Degus in constructing this structure was similar with that by primates: first they mainly constructed pairs of the objects and then proceeded to triplets. The relation between the evolutionary emergence of hierarchical construction and language acquisition is discussed.