Assessing larger-than rule learning in African grey parrots (Psittacus erithacus).
Many animals discriminate between magnitudes (e.g., in size, quantity, volume, length) that have fitness implications. Accumulated experience may facilitate the formation of relational rules that can be applied in novel contexts. However, the extent to which animals can form a relational rule, and are able to apply it to novel contexts remains a core focus when understanding the evolution of cognition. Here, we assessed the ability of African grey parrots o acquire the relative larger-than rule in size or quantity discrimination, and if so, how this was learned. Eight captive parrots initially participated in a natural preference test (NPT) to assess their prior preference for a larger amount of seeds. Each parrot was then randomly selected to either acquire the larger-than rule in size or quantity in a basic training (BT). They then participated in transfer training (TT) to evaluate their ability to apply the learned rule to novel stimulus pairs, and a final transfer test (FTT) to assess whether the parrots could generalise the learned rule to unseen stimulus pairs beyond the training range. Six parrots successfully completed both training and the test, with only one parrot, Sensei, passing the quantity discrimination FTT. More detailed analyses showed that the parrots showed varied performance in the TT, but as a group, showed limited transfer in the TT, suggesting the use of associative learning through increased experience in BT. They also showed better performance if a stimulus pair had a larger difference (Webers law). The success of Sensei was attributed to extensive TT alongside his quick natural preference toward larger amounts. These results suggest that repeated exposure to TT stimulus pairs increases familiarity with the stimulus pairs, which can facilitate task success, but individuals vary in their ability to acquire relational rules.