Crossbills (Loxia curvirostra) are able to form the "larger than" concept.

An original method for studying cognitive abilities in largely wild passerine birds was developed. Studies of five crossbills (Loxia curvirostra) showed that this approach could be used to assess their ability to form concepts. All five crossbills learned selection rules for the "larger number" feature over the range "1-10." The birds successfully transferred this to stimuli significantly different from those used in training, which were not comparable in terms of all quantitative properties, but only some (only area or number). Only one bird was able to transfer the learned choice rule to multiples in a new range ("10-20"). Thus, the ability of representative small forest passerine birds to form the "larger than" concept was demonstrated.