An African gray parrot (Psittacus erithacus), Alex, trained to label vocally collections of 1-6 simultaneously presented homogeneous objects, correctly identified, without further training, quantities of targeted subsets in heterogeneous collections. For each test trial Alex was shown different collections of 4 groups of items that varied in 2 colors and 2 object categories (e.g., blue and red keys and trucks) and was asked to label the number of items uniquely defined by the conjunction of 1 color and 1 object category (e.g., "How many blue key?"). The collections were designed to provide maximal confounds (or distractions) and thus replicate the work of Trick and Pylyshyn (1989) on humans. Humans count rather than subitize under such conditions. Alex's results (83.3% overall accuracy) are therefore discussed in terms of their relation to human numerical competence, particularly with respect to counting.
Pepperberg, I. M. (1994). Numerical competence in an African gray parrot (Psittacus erithacus). Journal of Comparative Psychology, 108(1), 36.