The Avian Brain

This post is based on “The Genius of Birds,” a book by Jennifer Ackerman. The chickadee is more than just a bird of verve and agility. It’s also acrobatic in its aptitudes, curious intelligent, and opportunistic with a prodigious memory. It is a bird masterpiece beyond in the words of Forbush. The chickadee family rates right up there with woodpeckers on Lefevbre’s IQ scale. Chickadees stash seeds and other food in thousands of different hiding places to eat later. They can remember where they put a single food item for up to six months. And they do this with a brain roughly twice the size of a garden pea. The chickadee has double the brain size of birds in the same body-weight range, such as a flycatcher or swallow. Many bird species have surprisingly large brains for their body size. Scientists call them hyper inflated, much like our brains.

Birds have condensed genomes, which may be an adaptation to powered flight. Birds have the smallest genomes of any amniote, the group of animals, including reptiles and mammals, that lay their eggs on land. The typical mammal has a genome ranging from 1 billion to 8 billion base pairs, whereas in birds it hovers at around 1 billion. This is the result of fewer repeat elements and a large number of so-called deletion events, in which DNA has been expunged over evolutionary time. This more compressed genome might allow a bird to regulate its genes more rapidly to meet the requirements of flight.

Birds evolved from dinosaurs during the Jurassic period, 150 million to 160 million years ago. Paleontologist Stephen Brusatte of the University of Edinburgh says that we find that there is no clear distinction between ‘dinosaur’ and bird.’ A dinosaur didn’t just change into a bird one day. The bird body plan began early and was assembled gradually, piece by piece over 100 million years of steady evolution.

Birds have their eggheads and their pinheads. Not all birds have big brains for their body size. For example, birds of a similar size, a crow (with a brain of 7 to 10 grams) and a partridge (only 1.9 grams) have different sized brains. But two smaller birds, the great spotted woodpecker (with a brain of 2.7 grams) and the quail (0.73 gram) have different sized brains.

Reproductive strategy plays a role in brain size. The 20% of bird species that are precocial—born with their eyes open and able to leave the nest within a day or two—have larger brains at birth than altricial birds. These are born, naked, blind, and helpless and remain in the nest unit they’re as big as their parents, and only then do they fully fledge. Precocial birds, such as shorebirds, typically take to life straightaway. Though their brains are relatively large at hatching—allowing them to catch and eat an insect or run short distances when only days old—they don’t grow much after birth, so they end up smaller than the brains of altricial birds. So, nest sitters end up with bigger brains than nest quitters.

Brain size is also correlated with how long a bird stays in its nest to apprentice with its parents after fledging. The longer the juvenile period, the bigger the brain, perhaps so that a bird can store all it learns. Long childhoods are characteristic of most intelligent animal species.

Birds experience the same cycles of slow-wave sleep and rapid eye movement (REM) that humans do. Scientists believe that these patterns of brain activity play a crucial role in the growth of big brains. Birds rarely have REM sleep longer than 10 seconds, packaged into hundreds of episodes per sleep period, while humans have several bouts of REM sleep per night, each lasting ten minutes to an hour. For both mammals and birds, REM sleep might be especially needed for the early development of the brain. Newborn mammals such as kittens have much more REM sleep than adult cats. Human babies may spend up to half their sleep in the REM stage, whereas for adults, it’s about 20%. Similarly young owlets have more REM sleep that older owlets.

Both birds and humans have periods of deep, slow-wave sleep in direct proportion to how long they’ve been awake. And in both birds and humans, the brain regions used more extensively in waking hours sleep more deeply during subsequent sleep.

A research team headed by Niels Rattenborg at the Max Planck Institute of Ornithology made use of a bird’s ability humans do not have. Birds can modulate their deep sleep by opening one eye, limiting the slow-wave sleep to only one half of the brain while keeping the other half alert. It takes very little thought to understand how such a capability is beneficial to birds. The team built a little movie theater for several pigeons, blocked one eye in each of them. and showed them David Attenborough’s The Life of Birds. After staying awake watching the film for eight hours with a single eye, the birds were allowed to sleep. Studies of their brain activity showed deeper slow-wave sleep in the visual processing region of the brain connected to the stimulated eye.

Rattenborg says that both humans and birds showing this kind of localized brain effect suggest that slow-wave sleep may play a role in maintaining optimal brain functioning. “overall, the parallels between mammalian and avian sleep raise the intriguing possibility that their independent evolution may be related to the function served by the pattern of sleep: the evolution of large, complex brains in both birds and mammals.”

Erich Jarvis says, “About 75% of our forebrain is cortex and the same is true for birds, particularly species of songbirds and parrots. They have as much ‘cortex’, relatively speaking, as we do. It’s just not organized the way ours is.” The author continues, “Whereas the nerve cells in a mammal’s neocortex are stacked in six distinct layers like plywood, those in the bird’s cortex like structure cluster like cloves in a garlic bulb. But the cells themselves are basically the same, capable of rapid and repetitive firing, and the way they function is equally sophisticated, flexible, and inventive. Moreover, they use the same chemical neurotransmitters to signal between them. And perhaps most important, bird and mammal brains share similar nerve circuits, or pathways between brain regions—which turns out to be vital for complex behavior. It’s the connections, the links between brain cells, that matter in the matter of intelligence. And in this regard, bird brains are not so different from our own.

Irene Pepperberg offers this computer analogy. Mammalian brains are like PCs, she says, while bird brains are like Apples. The processing is different, but the output is similar.

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