On the brain
bird brain is described in most dictionaries as a person who is stupid, unintelligent or foolish, and as early as the 1600s such a person would be called ‘bird-witted’. The reason for this is probably linked to the small size of a bird’s brain. However, a recent study showed that some birds have twice the number of neurons compared to primate brains of a similar mass and use about a third of the amount of energy that an equivalent mammal brain would need. All of this means that birds in fact have a more efficient brain than we do.
The large density of neurons explains why corvids and parrots are known to be the most intelligent bird species, being able to manufacture and use tools, solve problems and recognise themselves in a mirror. One famous Grey Parrot called Alex could understand numbers, colours and shapes and knew at least 150 words. Crows can remember a human face several years after seeing it and can count up to seven.
The structure of the avian brain has many similarities to that of the mammalian brain, with two cerebral hemispheres, a cerebellum and a medulla oblongata. Bird brains have a thin cerebral cortex and also possess a hyperpallium, which controls intelligent behaviour. Comparisons of the number of neurons in the hyperpallium show that in crows there are twice as many as in pigeons and chickens. One special area, the wulst, is linked to visual recognition, and so is large in owls, for example, which have good binocular vision. Songbirds have what is called ‘Area X’, which is involved with vocal learning when young, while parrots have a different pathway, which enables them to learn new sounds at any age.
Although a macaw and a pheasant are of roughly the same weight, a macaw has a brain nearly five times the size of a pheasant’s. The brain of an ostrich is only the size of a walnut and weighs 27 g, which is a mere 0.015% of its total body weight. The much smaller Raven has a 15.4-g brain, this being nearly 2% of its body weight. Remarkably, a tiny hummingbird has a brain the size of a pea and yet this makes up 4.2% of its weight. One of the reasons for such a relatively large brain is that it can move in many more directions than other birds when flying and so has to make a lot of high-speed decisions. It also has a large hippocampus, which enables it to remember every individual flower it has visited and when to return there for its next feed.
One study recently showed that brain size (relative to body size) in birds depends on the amount of parental care that the species receives. Altricial birds, which include corvids and parrots, need a large amount of care after hatching and some crows may be looked after by their parents for up to four years. Fascinatingly, birds which live on islands have also been shown to have larger brains than their mainland counterparts.