Although human hearing has been studied for centuries, new technological breakthroughs are now making it possible for scientists to better than ever understand how animals hear, and what role hearing plays for various species.
Mice: Communicating and Hearing in a Language of their Own
It’s been known since the fifties that mice produce “supersonic squeaks” —shrieks of a pitch so high that the human ear can’t register them. However, it’s only recently that scientists have discovered that those limitations go both ways: mice are just as deaf to the lower pitches humans use to communicate. So, while mice can hear shrill human screams, they don’t register normal conversation.
Dolphins and Toothed Whales: Hearing Shapes
When scientists Donald Griffin and Robert Galambos first proved in 1938 that bats successfully hunt insects and birds in the dark of night using echolocation (also called biosonar), the discovery revolutionized the world, enabling the development of radar technology employed only a few years later in World War II. But scientists are still not sure what role echolocation plays for marine animals like dolphins and whales. Because only one family of whale species, the carnivorous group known as toothed whales, employs echolocation, it is thought that echolocation primarily evolved for hunting purposes.
Hearing for Squids and Octopi: Listening for their Lives
Until recently, the question of whether cephalopods (the genus that includes octopi, squid, cuttlefish, and nautiluses) can hear remained hotly contested. Fish are able to hear using pockets of air in their skulls which allow them to feel rapid and minute changes in pressure created by external vibrations. Cephalopods lack those air pockets, suggesting that they might be deaf. But fisherman and divers continued to report that cephalopods responded to sounds like those made by knocking on the side of a boat or dropping stones underwater. In 2009, it was conclusively proven that squids and octopi can hear (to a limited extent) by an entirely different method — using an organ called a statocyst, a sac-like structure that consists of a mineralized mass and tiny sensitive hairs. This is thought to be an adaptive response to predation by whales and dolphins, which communicate vocally.
Natural habitats also seem to have played a role in the evolution of hearing in cephalopods. Octopi mostly hear very low-pitch sounds, which makes sense because high-pitch sound waves would be disrupted by the rough texture of the ocean beds and coral reefs where octopi tend to live. Squid, which live in open water, are better at hearing high-frequency sounds.
Birds: Hearing what they want to Hear
Although birds’ hearing is exceptionally good, biologists have noticed that it’s better at certain times of year, a discovery that may have ramifications for human hearing research as well. During mating season, female birds become highly attuned to certain pitches, mainly ones used by males in their mating calls. Estrogen is thought to play a role in this increased sensitivity. Higher estrogen levels have previously been linked to better hearing in humans and fish.
Hearing aids and cochlear implants are currently available for dogs. For the human species, Audicus hearing aids are a sleek and affordable option… and almost as discreet as some of the hearing solutions in the animal kingdom.
Sources: Societyandanimalsforum, BBC, Smartplanet