Chicks vs. Infants: 4-1. Numerical discrimination in day old domestic chicks (Gallus gallus)

The aim of this work is to investigate the domains of the two systems that are considered to be at the basis of the non-verbal numerical skills. These would represent, respectively, small values (‹3), and large magnitudes (›4). Intriguing experiments report as human infants (of 10-12 months, an age in which infants are able to distinguish between large numerousness such as 8vs.12) discriminate between 1vs.2, 1vs.3, 2vs.3, but not between 1vs.4. This suggests the independence of the non-verbal numerical systems. Other researches though indicate a continuity in the representation of small and large numbers. Experimental evidence, reporting as day-old chicks are able to process subsequent additions and subtractions such (4-1)vs.(1+1), supports this last hypothesis. Here, newly-hatched domestic chicks were reared with 5 identical imprinting objects. On day 3, subjects underwent free choice tests between sets of objects once the sets had disappeared (one object at a time) each behind one of two identical opaque screens. In all comparisons (4vs.1, 5vs.1 or 4vs.2), chicks spontaneously inspected the screen occluding the larger set. Our findings suggest a continuity in the processing of small and large numerousness in this species, the difference with the infants’ data demands additional investigation regarding the origins and the evolution of the systems involved.