Scientists have recently made some remarkable discoveries about non-human sounds. With the aid of digital bioacoustics – tiny, portable digital recorders similar to those found in your smartphone – researchers are documenting the universal importance of sound to life on Earth.
By placing these digital microphones all over Earth, from the depths of the ocean to the Arctic and the Amazon, scientists are discovering the hidden sounds of nature, many of which occur at ultrasonic or infrasonic frequencies, above or below human hearing range. Non-humans are in continuous conversation, much of which the naked human ear cannot hear. But digital bioacoustics helps us hear these sounds, by functioning as a planetary-scale hearing aid and enabling humans to record nature’s sounds beyond the limits of our sensory capacities. With the help of artificial intelligence (AI), researchers are now decoding complex communication in other species.
As scientists eavesdrop on nature, they are learning some astonishing things. Many species that we once thought to be mute actually make noise – lots of it, in some cases. For example, research by Camila Ferrara at Brazil’s Wildlife Conservation Society has demonstrated that Amazonian sea turtles make more than 200 distinct sounds. Ferrara’s research showed that turtle hatchlings even make sounds while still in their eggs, before they hatch, to coordinate the moment of their birth. Ferrara’s acoustic research also revealed that mother turtles wait nearby in the river, calling to their babies to guide them to safety, away from predators: the first scientific evidence of parental care in turtles, which were previously thought to simply abandon their eggs.
And this is likely to be only the opening chapter in discoveries about turtle noise. Gabriel Jorgewich-Cohen at the University of Zurich recently collected recordings from more than 50 species of turtles previously thought to be non-vocal.
Scientists are also learning that vocally active species – like bats – make sounds which contain much more complex information than previously thought. Bat echolocation, for example, was discovered nearly a century ago. But only recently have researchers begun deciphering the sounds that bats make for other purposes. By recording many hours of bat vocalizations and decoding them using AI algorithms, scientists have revealed that bats remember favors and hold grudges; socially distance and go quiet when ill; and use vocal labels that reveal individual and kin identity. Male bats learn territorial songs in specific dialects from their fathers and, much like birds, sing these songs to defend territory and attract mates, which scientists characterize as culture.
Research by Mirjam Knörnschild in Costa Rica with sac-winged bats has demonstrated that mother bats babble to their babies in “motherese”, in a manner similar to humans; baby bats learn to vocalize this way. Until recently, scientists had no idea that bats were capable of vocal learning, or conveyed such complex information in their vocalizations.
Acoustic tuning is also widespread in nature. Coral and fish larvae find their way back home by imprinting on the unique sounds made by the reef where they were born. Moths have developed echolocation-jamming capabilities to hide themselves from bat sonar. Flowers and vines have evolved leaves to reflect echolocation back to bats, as if they were luring their pollinators with a bright acoustic flashlight. In response to the buzz of bees, flowers flood themselves with nectar. Plants respond to some sound frequencies by growing faster; and some species – including tomatoes, tobacco and corn seedlings – even make noise, although well above our hearing range.
Yossi Yovel at Tel Aviv University, whose research bridges neuroscience and ecology, trained an artificial intelligence algorithm to listen to tomato plants; the algorithm learned to discern whether the plants were dehydrated or wounded, just by listening to the different sounds they were making. Although humans cannot hear the ultrasonic frequencies at which plants make noise, we know that some insects and animals can. Could plants be signaling their state – whether healthy or distressed – to other creatures? Nature is full of resonant mysteries of sound, of which humans are only beginning to become aware.
Scientists are now attempting to use these digitally enabled discoveries to develop tools for interspecies communication with creatures as diverse as honeybees and whales, raising both ethical and philosophical questions. Do we have the right to eavesdrop on non-humans and gather data without their consent? Does the existence of complex communication in animals challenge the claim that humans, alone, possess language? What are the risks of engaging other species in AI-mediated conversations, when we know about the biases embedded in AI systems?
As we grapple with these future-oriented questions, we should not forget about the pressing challenge of noise pollution, the reduction of which can have immediate, positive and significant impacts for non-humans and humans alike. Hushing the human cacophony is a major challenge of our time. Digital listening reveals that we have much more to learn about non-humans, and provides new ways to protect and conserve the environment. Perhaps one day we will invent a zoological version of Google Translate. But first we need to learn how to listen.
Dr. Karen Bakker is a Professor at the University of British Columbia, a Fellow at the Harvard Radcliffe Institute for Study, and author of The Sounds of Life: How Digital Technology is Bringing Us Closer to the Worlds of Animals and Plants.