Bird brains are far smaller than human brains. Despite this, they nevertheless pack a punch in terms of proportion. Many birds have large craniums for their body size, which is an essential and costly evolutionary characteristic. (Brain cells are extremely greedy, requiring up to ten times their weight in oxygen and blood flow.)
But why does a bird require so many cells and neurons? According to experienced scientific writer Jennifer Ackerman, who explores the various manifestations of bird intelligence in her latest book, The Genius of Birds, the list is nearly endless. From mockingbirds that learn hundreds of “languages” to pied babblers who “kidnap” chicks from other families, Ackerman seeks out the brainiest animals and shows their unique mental powers through entertaining narratives. Audubon exchanged emails with Ackerman about these stories, as well as the many mysteries surrounding birds and their intellect.
Nagoya University physiologists have gained a better grasp of the cerebral circuitry in birds that allows them to determine where a certain sound is coming from. Their findings, which were published in the journal Science Advances, could help scientists grasp the fundamentals of how mammalian brains compute the time difference between a single sound coming at each individual ear, a concept known as ‘interaural time difference.’ This capacity is essential for sound localization.
Many animals, including humans, use the temporal difference of a sound reaching both ears as a clue for sound source localization. We’d like to see if the link we discovered between brain function and structure is universal in other species. Extending our research to mammalian brains will be critical for understanding the fundamental principle of interaural time difference detection that birds and mammals share with humans.
Rei Yamada
“Animals can execute accurate interaural time difference detection for sounds of a wide range of frequencies,” says Rei Yamada, a cell physiology specialist at Nagoya University’s Graduate School of Medicine. The neuronal circuitry for this procedure is so sophisticated that the multiple branches extending from a single nerve cell, known as dendrites, receive a specific sound frequency from one or both ears. However, it is not yet obvious how all of this comes together to enable interaural time difference detection.
Yamada and his colleague Hiroshi Kuba were curious about the technique. They used lasers to stimulate excitatory receptors in a region of the brain responsible for sound localization in chicken brain slices. This was followed by modeling trials to help them understand the significance of their original findings.
They noticed that nerve junction, known as synapses, were especially dense at the ends of specialized long dendrites dedicated to transmitting impulses from low-frequency sounds. Contrary to popular belief, this clustering reduced the power of signal transmission down the length of the dendrite, resulting in a weaker signal by the time it reached the nerve cell. This technique, on the other hand, allowed the nerve cell to sustain powerful inputs entering through dendrites dedicated to each ear, allowing it to carry out the necessary time difference and location computation operations.
Birds, in fact, make better use of the space allowed for their tiny brains by packing in more neurons than mammals. But what exactly characterizes a bird as intelligent? Scientists believe the definition should be expanded.
“The ability to fly to Argentina, return, and land in the same bush—we don’t respect that intelligence in a lot of other organisms,” says Kevin McGowan, a crow expert at Cornell Lab of Ornithology in Ithaca, New York. “We’ve narrowed the field to things we believe only we can do.” However, when it comes to standard intelligence, such as replicating human speech or problem-solving, “it always comes down to parrots and corvids,” according to McGowan.
“Many animals, including humans,” Yamada explains, “use the temporal difference of a sound reaching both ears as a clue for sound source localization. We’d like to see if the link we discovered between brain function and structure is universal in other species. Extending our research to mammalian brains will be critical for understanding the fundamental principle of interaural time difference detection that birds and mammals share with humans.”
