Humans, including infants, and many other species have a capacity for rapid, nonverbal estimation of numerosity. However, the mechanisms for number perception are still not clear; some maintain that ...

Crows recently demonstrated an understanding of the concept of zero. It’s only the latest evidence of animals’ talents for numerical abstraction — which may still differ from our own grasp of numbers.

While some experiments try to test animals' perception of quantities in natural settings, others use training paradigms that offer experimenters more control over the conditions. All face the obstacle ...