They have hard shells, they amble slowly. They like lettuce. You don't hear alot about turtle's auditory functionality. That might be because you can't see a turtle's ears. The sides of turtles' heads are smooth; their ears exist as interior canals, not sticking out from their heads like most mammals'. But turtles still have an ability to hear. Terrestrial turtles and sea turtles hear in the same way.
Hearing on Land
Turtles who live on land need to hear so they can avoid predators or find prey, but they don't hear in the same way people do. A person's outer ear is shaped to help draw sounds in toward the outer ear, but turtles have no outer ear. They have thin flaps of skin covering internal ear bones. The skin flaps allow vibrations and low-frequency sounds in the ear canal -- so the turtles can hear to some extent, but their hearing isn't sensitive. Turtle ears can sense air displacement, such as when a large predator is near, or detect vibrations coming off the ground, such as when a tasty frog takes a leap nearby. Turtles might never hear the higher-frequency sounds of birds chirping, but they would likely detect the sounds of birds flying quickly out of a bush by sensing the vibrations and hearing the lower-frequency sound of wings flapping. They use their ears in conjunction with more powerful senses, such as smell, to find prey and dodge predators.
Sea turtles have basically the same ear structure as terrestrial turtles, which leads many scientists to believe both types were originally aquatic. Sea turtles also hear low frequencies and sense vibrations, the water acting as a conduit to help them hear slightly better than their land-living cousins. The skin covering makes more sense in the water -- sea turtles need to keep water out while allowing vibrations in. They don't use hearing to help them navigate underwater, but their ears help detect changes in water pressure that might indicate a predator is nearby.
Hearing Like a Turtle
Behind the skin flaps, turtles have middle ear bones that direct vibrations down the ear canal. Turtles don't have eardrums, but they have small bones in their inner ears that help distinguish sounds and vibrations. The inner ears pass the sounds along to the brain's hearing center for interpretation. Because hearing is a secondary sense for turtles, the brain's hearing center is small.
What They Do Best
Without sensitive hearing, turtles rely more on other senses such as vision and smell. Their vision is much better than their hearing, allowing them to see colors, shapes and patterns. Sea turtles see better underwater than on land, but terrestrial turtles don't suffer from the same handicap. All turtles have a strong sense of smell as well, helping them avoid predators, find food and find each other when mating time arrives.
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- North American Box Turtles: A Natural History; C. Kenneth Dodd
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