It is getting to be common knowledge that some birds can count. Recent research (citation below) has shown some of the details of how crows handle numbers. They have a different brain architecture from mammals but in some ways show similar functions to our neo-cortex in their endbrain association area. This points to possible convergent evolution.
Ditz and Nieder planted electrodes in the endbrain of crows and recorded activity of NLC (nidopallium caudolaterale) neurons. The birds were shown groups of items and the NCL neurons shown activity to specific numbers of items. The activity of a particular neuron peaked at a particular number.
Here is the abstract: “It is unknown whether anatomical specializations in the endbrains of different vertebrates determine the neuronal code to represent numerical quantity. Therefore, we recorded single-neuron activity from the endbrain of crows trained to judge the number of items in displays. Many neurons were tuned for numerosities irrespective of the physical appearance of the items, and their activity correlated with performance outcome. Comparison of both behavioral and neuronal representations of numerosity revealed that the data are best described by a logarithmically compressed scaling of numerical information, as postulated by the Weber–Fechner law. The behavioral and neuronal numerosity representations in the crow reflect surprisingly well those found in the primate association cortex. This finding suggests that distantly related vertebrates with independently developed endbrains adopted similar neuronal solutions to process quantity.”
It is interesting, and confirms other bird studies, that:
- they can put items in categories in order to count them,
- they can make a set of the items in a particular category,
- they can assess the quantity on a logarithmic scale (like 1, 2, 3, 4, 6ish, 9ish, 15ish etc),
- this is an abstract quantity and does not depend on the arrangement, size etc. of the items.
Citation: Helen M. Ditz and Andreas Nieder. Neurons selective to the number of visual items in the corvid songbird endbrain. PNAS, June 2015 DOI: 10.1073/pnas.1504245112