Grey parrot numerical competence: a review

A review of decades of work with a grey parrot trained to use English labels. Tasks included labelling the number of objects in a set, answering questions about which colour or shape had a given quantity, and responding to questions about sets containing several categories at once.

Studied in

Psittacus erithacus

Sample size

1 principal subject across a long-running training programmeThe grey parrot Alex, studied over decades.

The parrot labelled quantities up to six accurately, answered questions requiring a specific subset to be counted rather than the whole set, and showed some understanding of ordinality and of the absence of a quantity.

• One individual, trained intensively over decades; not a sample from which species-typical ability can be read.
• The training method makes inadvertent cueing a standing concern, addressed but not eliminated.
• A review rather than a single controlled experiment.

• A sense of number

  Many animals can tell "more" from "less" — far fewer can actually count

• Common raven

  Ravens can copy human words. There is no evidence they mean anything by them