Researchers find songbirds and parrots can have as many, sometimes more, neurons packed into their brains than mammals - even monkeys and apes

Some can count, many make tools, and others recognise themselves in the mirror. But how birds pull off such complex feats with so little brain matter has long had scientists scratching their heads.

Now an answer may finally be at hand. Researchers who studied 28 bird species found that songbirds and parrots can have as many, and sometimes more, neurons packed into their brains than mammals - even monkeys and apes.



The tiny but densely-packed neurons are thought to endow birds with cognitive abilities that far outstrip expectations and which in some cases are more than a match for primates with similar-sized brains.



“For a long time there has been this enigma that birds have rather small brains but are actually incredibly clever,” said Pavel Němec at Charles University in Prague. “They are able to do things that we once thought only apes and humans could do. There was a mismatch between their brain size and their cognitive abilities.”



In what Němec described as one of the hardest parts of the study, he and his co-workers bought or captured a variety of birds, ranging from starlings and zebra finches to jackdaws and parakeets, and set about examining their brains. Having removed and fixed the animals’ brains, the team set about dissecting the key regions. Each brain part was then ground up and mixed into a solution in which the neurons could be dyed and counted.



Facebook Twitter Pinterest For each species, the total number of neurons (in millions) in their brains is shown in yellow, the number of neurons (in millions) in their forebrains is shown in blue and their brain mass (in grams) is shown in red. The scale bar in the lower right is 10 mm. Photograph: Suzana Herculano-Houzel/ Vanderbilt University

While birds have tiny brains, they turn out to have phenomenal numbers of neurons. The macaw’s brain is no larger than a walnut, but it has more neurons in its forebrain - a region crucial for intelligent behaviour - than the macaque, which has a brain the size of a lemon. Both sulphur-crested cockatoos and bushbabies have brains that weigh about 10g, but the cockatoo has two billion neurons, twice as many as the bushbaby.



Parrots, songbirds and corvids, including ravens, rooks and crows, had the highest densities of neurons in their forebrains, offering up the idea that what the birds lack in size, they more than make up for in sheer numbers of brain cells. Details of the study are published in Proceedings of the National Academy of Sciences.



“This pretty much answers the question we began with: how can these birds be so clever with such small brains?” said Němec. “The answer is that there are so many neurons, their computing power is comparable to that of primates.”



The more scientists study birds, the more they uncover about their unexpected talents. In 2002, an Oxford team watched with delight as a New Caledonian crow bent a piece of wire into a hook and fished food from a container. They are not the only birds to use tools. Other researchers have documented the counting skills of African grey parrots and the ability of magpies to recognise their own reflections.



“For a long time having a ‘bird brain’ was considered to be a bad thing,” said co-author Suzana Herculano-Houzel at Vanderbilt University in Nashville, Tennessee. While no concrete link between intelligence and numbers of neurons has been established, the scientists argue that the huge numbers of neurons in the birds’ forebrains may give them more brainpower, gram for gram, than mammals.



Andreas Nieder, a neurobiologist at the University of Tübingen in Germany, said that the so-called endbrain, which includes the neocortex in mammals, and a structure called the pallium in birds, is considered a key site for intelligent behaviour.

“If some birds, most notably corvids and parrots, have far more numbers of neurons per brain mass than even primates, then this must have beneficial behavioural consequences. These new findings could definitely help to explain why some birds, such as jays, crows and ravens, excel in their cognitive skills,” he said. “This is because more neurons per brain mass allow for more connections between neurons and larger networks, and this, in turn, enables faster and more powerful processing of information.”



Němec is now analysing the brains of more birds, including pigeons, waterfowl and chickens, and later hopes to move on to studying how their brains are wired up. “We would like to look at whether avian neurons have similar numbers of connections to those in primates, but that is for a large future project,” he said.