Birds that sing or use tools have about as many neurons in their brains as monkeys do.

Pavel Němec at Charles University in Prague and his colleagues measured the brain size of birds from 28 species, and counted the number of cells in the organs. They found that intelligent birds such as parrots and songbirds have larger brains relative to their body size, with much higher neuron density, than do less-intelligent birds such as chickens. Moreover, a higher proportion of the neurons were located in the forebrain, which controls higher cognitive function.

Such high neuronal densities could be contributing to the intelligence of the birds, the authors suggest.

Proc. Natl Acad. Sci. USA (2016)