No Offense! “Bird Brain” Is a Compliment
Next time someone calls you a birdbrain, smile and say “thank you.” Our feathered friends come well equipped with hardware and software for complex behaviors. A new study published in the Proceedings of the National Academy of Sciences puts birds on par with macaques and other mammals, and even suggests they can think.
Here’s what the news from Vanderbilt University says about the results of a detailed study by researchers primarily from the University of Prague, with additional team members from Austria, Brazil, and the United States:
The macaw has a brain the size of an unshelled walnut, while the macaque monkey has a brain about the size of a lemon. Nevertheless, the macaw has more neurons in its forebrain — the portion of the brain associated with intelligent behavior — than the macaque.
That is one of the surprising results of the first study to systematically measure the number of neurons in the brains of more than two dozen species of birds ranging in size from the tiny zebra finch to the six-foot-tall emu, which found that they consistently have more neurons packed into their small brains than are stuffed into mammalian or even primate brains of the same mass. [Emphasis added.]
How is this possible? The answer includes miniaturization and efficient packaging:
That is possible because the neurons in avian brains are much smaller and more densely packed than those in mammalian brains, the study found. Parrot and songbird brains, for example, contain about twice as many neurons as primate brains of the same mass and two to four times as many neurons as equivalent rodent brains.
Not only are neurons packed into the brains of parrots and crows at a much higher density than in primate brains, but the proportion of neurons in the forebrain is also significantly higher, the study found.
The scientists note that even despised birds like pigeons show much the same brain power. Powered flight, obviously, takes a lot of hardware and software to operate in any bird; how much so in the supreme flyers Illustra Media showed in Flight: The Genius of Birds: starlings, Arctic terns, and especially the tiny hummingbirds? Dr. Suzana Herculano-Houzl, lead author of the study, shows her delightful surprise in video clips in the news item. The small heads of birds belie the observations of complex behaviors they perform.
But it’s not just routine tasks the brains must perform. Some birds can remember where they stored hundreds of seeds. Birds have been observed to hide a seed while another bird is watching, then move it when the neighbor is gone — indicative of a possible ‘theory of mind’ that shows planning and recognizing what the other bird is thinking.
The study provides a straightforward answer to a puzzle that comparative neuroanatomists have been wrestling with for more than a decade: how can birds with their small brains perform complicated cognitive behaviors?
The conundrum was created by a series of studies beginning in the previous decade that directly compared the cognitive abilities of parrots and crows with those of primates. The studies found that the birds could manufacture and use tools, use insight to solve problems, make inferences about cause-effect relationships, recognize themselves in a mirror and plan for future needs, among other cognitive skills previously considered the exclusive domain of primates.
Indeed, crows have shown the ability to solve a puzzle made famous in an Aesop’s fable (Reuters): dropping stones in a pitcher to raise the water level in order to get a drink. New Caledonian crows have shown the ability to use three tools in succession to reach a food source (BBC News). Owners of parrots know the cleverness of their pets; their ability to mimic human speech and singing is astonishing. Some cockatiels can even do the Riverdance.
Finding such detail and complexity in the brains of birds poses a serious evolutionary problem. The old progressive gradualism of Darwin saw humans at the pinnacle of evolution, with everything that came before less advanced. To find that birds, so completely distant from mammals on the Tree of Life, having comparable brains to primates is unexpected from a Darwinian view.
In the second video clip from Vanderbilt, Herculano-Houzl struggles to give an evolutionary account. She intimates that birds evolved intelligence first and then kept it at that level while mammals, evolving separately, arrived at comparable intelligence later. That only compounds the problem. The paper further compounds the problem by postulating that “songbirds and parrots independently evolved vocal learning pathways by duplication of preexisting, surrounding motor circuits.” But duplication does not add information; it’s an accident. The statement amounts to saying bird intelligence happened by chance.
As Denyse O’Leary has explored here at Evolution News, intelligence does not require a specific type of brain. What better way to dismiss evolutionary pathways than to show independent brain types with similar capabilities for cognition and intelligence? It’s similar to Tim Standish’s comment in Living Waters about a mind being able to know a solution to a problem (in that case, magnetic navigation) and applying it over and over again in different contexts. Isn’t that a better explanation than admitting ignorance and tossing out suggestions?
What ultimate mechanisms drive the evolution of the enlarged, neuron-rich telencephalon, which sets parrots and songbirds apart from the more basal birds we examined, remains poorly understood. We suggest that this expansion has been due to simultaneous selective pressures on cognitive enhancement and an evolutionary constraint on brain size, which may stem from the constraints on body size imposed by active flight.
One cause we know that can optimize multiple, competing constraints is intelligence. When a cause is known to be necessary and sufficient to explain a phenomenon, that cause should be preferred as the vera causa (true cause). It would seem that intelligent causes are best equipped to take up the challenge the researchers leave at the end of their paper:
Our finding of greater than primate-like numbers of neurons in the pallium of parrots and songbirds suggests that the large absolute numbers of telencephalic neurons in these two clades provide a means of increasing computational capacity, supporting their advanced behavioral and cognitive complexity, despite their physically smaller brains. Moreover, a short interneuronal distance, the corollary of the extremely high packing densities of their telencephalic neurons, likely results in a high speed of information processing, which may further enhance cognitive abilities of these birds. Thus, the nuclear architecture of the avian brain appears to exhibit more efficient packing of neurons and their interconnections than the layered architecture of the mammalian neocortex.
Further comparative studies on additional species are required to determine whether the high neuronal densities and preferential allocation of neurons to the telencephalon represent unique features of songbirds, parrots, and perhaps some other clades like owls, or have evolved multiple times independently in large-brained birds. More detailed quantitative studies should assess the distribution of neurons among various telencephalic regions involved in specific circuits subserving specific functions. The results, combined with behavioral studies, will enable us to determine the causal relationships between neuronal numbers and densities and perceptual, cognitive, and executive/motor abilities, and greatly advance our understanding of potential mechanisms linking neuronal density with information-processing capacity.
Go ahead. With all this in mind, you can judge the credibility of the evolutionary explanation for yourself.