Arithmetic in newborn chicks

A previous study showed that chicks tend to approach the larger number of imprinted objects, irrespective of the number of objects they have been reared with. Newly-hatched domestic chicks were reared with five identical objects. On days 3 or 4, chicks underwent free choice tests in which sets of three and two of the five original objects disappeared (either simultaneously, or one by one), each behind one of two opaque identical screens. Chicks (N=17) spontaneously inspected the screen occluding the larger set (Exp. 1). Results were confirmed on a novel group of chicks (N=16) tested under conditions controlling for continuous variables (total surface area or contour length; Exp. 2). In the third experiment (N=20), after the initial disappearance of the two sets (first event) some of the objects were visibly transferred, one by one, from one screen to the other (second event). Thus, computation of a series of subsequent additions or subtractions of elements that appeared and disappeared, one by one, was needed in order to perform the task successfully. Chicks spontaneously chose the screen hiding the larger number of elements at the end of the second event, irrespective of the directional cues provided by the initial (first event) and final (second event) displacements. Results suggest impressive proto-arithmetic capacities in the young and relatively inexperienced chicks of this precocial species.