Spontaneous quantity discrimination in Capuchin, Spider and Howler monkeys: a preliminary investigation

This preliminary study investigates cognitive abilities and quantitative skills of Capuchin (Cebus capucinos), Spider (Ateles geoffroyi) and Howler (Alouatta palliata) monkeys through a series of tests using the free-choice method. The monkeys were presented with an inclined wooden plate on which two relevant stimuli, such as banana and beetroot sticks of different sizes were placed. The ratio between these sticks changed according to pseudo random sequence. If they were sensitive to the difference in quantities they were expected to select the larger one. Data suggest that spider and howler monkeys can grasp this difference while for the capuchins the result is unclear. This study is a starting point for future investigation that can be useful to understand the similiarity between human and non-human primates in quantitative skills.