“We need another and a wiser and perhaps a more mystical concept of animals,” the great nature writer Henry Beston wrote in his lovely century-old meditation on otherness and the web of life. “In a world older and more complete than ours they move finished and complete, gifted with extensions of the senses we have lost or never attained, living by voices we shall never hear.”

In the century since, we have come to unravel some of the wonders of the non-human sensorium — from the tetrachromatic vision of bees to the choral communication of migrating birds to the magnificent eye of the scallop. But few animal sensoria are more marvelously other than the ability of owls to see with sound, partway between synesthesia and advanced mathematical computation.

The visual system of owls is already astonishing enough, a hundred times more light-sensitive than that of a pigeon and capable of seeing ultraviolet light. Their enormous tubular eyes admit more daylight and have more cells to process photons than the eyes of birds with much sharper daytime vision. While the retinae of most birds are dominated by cones — photoreceptors tuned to bright light and tasked with color detection — the retinae of owls contain more than 90% rods, tuned to low light and sensitive to movement: the elements of hunting at night.

And yet the most extraordinary aspect of owl vision takes place not in their eyes but in their ears — theirs is one of the most sensitive auditory systems in nature, connected to one of the most computationally impressive brains.

In 1978, neurobiologists Eric Knudsen and Masakazu Konishi set out to illuminate its mysteries. Enlisting the help of an engineer who had worked on NASA’s Viking spacecraft — humanity’s historic reach for Mars — they sent a loudspeaker circling the head of an owl along a light-rail, traveling at a constant distance from the owl’s head: part halo and part ring of Saturn. Observing the neural response, they discovered something never before seen in nature — particular auditory neurons in the owl’s brain were responding only when a sound was coming from a particular direction: geolocation not by satellite but by sound, doing overground what cetaceans do underwater.

Recounting the research in her altogether fascinating book What an Owl Knows: The New Science of the World’s Most Enigmatic Birds (public library), Jennifer Ackerman writes:

By comparing the responses to sound by neurons in the cochlea of both ears, the brain builds a kind of multidimensional map of auditory space. This allows owls to fix the location of prey with speed and precision.

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Animals have brain maps for vision and touch, but these are built from visual images and touch receptors that map onto the brain through direct point-to-point projections. With ears, it’s entirely different. The brain compares information received from each ear about the timing and intensity of a sound and then translates the differences into a unified perception of a single sound issuing from a specific region of space. The resulting auditory map allows owls to “see” the world in two dimensions with their ears.

This research laid the foundation of studying how all animal brains appraise their environment through sound, leading to the development of a new diagnostic test for hearing loss in human infants — something notoriously difficult to test in nonverbal creatures. But the owl brain itself remained a frontier of fascination.

As other neuroscientists picked up the thread, they discovered that a barn owl’s brain performs complex mathematical computations to accomplish this spatial specificity, not merely adding and multiplying signals but engaging in a kind of probabilistic statistical calculation known as Bayesian inference. (If there is anything to settle the debate about whether humans have discovered or invented mathematics, here is blazing evidence that this is a fundamental language of nature in constant dialogue with living systems.)

Further research into the brain anatomy of owls revealed something even more astonishing: part of their hearing nerve branches off into the optical center of the brain, so that auditory input is processed by the visual system — literally a way of seeing with sound.

Couple the science of the owl with its poetry in Mary Oliver’s lovely meditation on the owl as a lens on the interconnectedness of life, then revisit the poetic science of how vision shaped consciousness.