It has long been observed that some species of bird, such as parrots and crows, have high levels of intelligence. They are able to use tools and solve puzzles on a level with some primates, despite having very small brains. This has confused many scientists over the years- how can an animal with such a small brain show such complex and intelligent behaviours?
This conundrum was solved by Olkowicz et al (2016), and published in PNAS. Superficially, the brains of birds and mammals look different, but they actually work using similar neuron organisation and have homologous regions. However, the brains of mammals are often much bigger than the brains of birds, so how can they have similar intelligence?
The researchers scanned the brains of 28 different species of birds, including parrots and crows, using an isotropic fractionator to discern the density of neurons, and compared the densities to mammals. Neurons are cells found in the nervous system, that transmit information as pulses of electrical system from the source to the brain, and then from the brain to create an action in response.
The results show that bird brains have many more neurons in them than equally sized mammal brains. Goldcrests have up to 64 million neurons in the Pallium brain region, which is 5x more neurons than in the mouse pallium. Parrots also had more neurons in some regions of their brain than Rhesus macaques, despite having a brain that is an order of magnitude smaller.
In conclusion, it appears that birds may have a higher-powered brain due to the sheer number and close-connectivity of their neurons. This is important, as studies of brains and neurons in other species may lead to further discoveries about the structure and function of the brain and central nervous system in humans.
The paper: Olkowicz et al. Bird have primate-like number of neurons in the forebrain. 2016. PNAS. 113(26). 7255-7260.