Discrimination of small quantities by fish (redtail splitfin, Xenotoca eiseni)

Further evidence for addition and numerical competence by a Grey parrot (Psittacus erithacus)

(2012) Irene M. Pepperberg   ANIMAL COGNITION

Evidence for Two Numerical Systems That Are Similar in Humans and Guppies

(2012) Christian Agrillo et al.   PLoS One

Small and large number discrimination in guppies

(2011) Laura Piffer et al.   ANIMAL COGNITION

Spontaneous discrimination of small quantities: shoaling preferences in angelfish (Pterophyllum scalare)

(2011) Luis M. Gómez-Laplaza et al.   ANIMAL COGNITION

Arithmetic in newborn chicks

(2009) R. Rugani et al.   PROCEEDINGS OF THE ROYAL SOCIETY B-BIOLOGICAL SCIENCES

Discrimination of small numerosities in young chicks.

(2008) Rosa Rugani et al.   JOURNAL OF EXPERIMENTAL PSYCHOLOGY-ANIMAL LEARNING AND COGNITION