Bad dog, smart dog: spontaneous discrimination of quantities in shelter dogs

Dogs’ co-domestication led to a series of modifications in their behaviour and cognition. Yet, how recent evolutionary history also interacts with developmental and experiential factors is often neglected. Here we tested shelter dogs in a two-alternatives free-choice task between different food quantities. Shelter dogs represent a heterogeneous population with high inter-individual variability, and we hypothesised that we could observe differences in cognitive performance between individuals depending on their attitude towards humans. Overall, we found that dogs preferred to approach the larger set of food (emmeans = 6.62. SE = 0.24, t = 28.17, p < 0.0001). However, consistently with our initial hypothesis, we observed that dogs that were evaluated as ‘less sociable’ by the keepers of the shelter succeeded already on their first trial (P(larger set) = 0.81, SE = 0.1, z = 2.31, p = 0.02), similar to what was observed in wolves and roaming dogs. Vice-versa, individuals that were evaluated as ‘highly sociable’ behaved at chance on the first trial and begun selecting the larger set only after a first interaction with the experimental setting (P(larger set) = 0.51, SE = 0.11, z = -0.7, p = 0.94), thus behaving alike to pet dogs. We discuss our results from both an experimental perspective, as in designing studies that account for multifaceted factors to reach a better understanding of cognition and behaviour in the Canis familiaris, and an applicative perspective, as in adding on current practices to facilitate the difficult process of inclusion of dogs in shelters, and possibly adoption.