Do smaller intelligent animals have a higher neuron density to account for their seeming intelligence? Otherwise, what?
It also may be the case that we are implying intelligence in some cases.
The responses these animals show may have been evolutionarily selected as it best for their survival. However, to us the benefits of these responses may not be directly visible. For example, sheep herding dogs may have a high degree of spatial and numerical capabilities since humans bred them for these traits.