All otters are semi-aquatic in nature, they can spend their days on land and also in water. Although some of them can forage on saltwater bodies, most otters live in freshwater habitats. Only sea otters almost exclusively live in the ocean; marine otters also venture to the sea but they prefer to be on land, hiding safely in between rocks.
The sea otters’ ancestors changed from being land-dwelling mustelids to becoming marine mammals 3 to 5 million years ago. And while that seems like a long time, it actually isn’t that much when you consider how long evolution takes!
Do you want to know how the sea otters’ ears work and how well they can hear? Tune into Floofmania’s article today to know how far the furry sea otters’ hearing has come in their early years of evolution.
How Well Do Sea Otters Hear?
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All 13 otter species of the Mustelidae family have relatively good hearing abilities, including sea otters.
As semi-aquatic marine mammals, sea otters have two unique hearing sensitivity ranges when they’re above the water surface and underwater.
But a handful of researchers found that sea otters aren’t that well-adapted to hearing sounds underwater, which is surprising!
Sea otters also have a relatively low-frequency hearing on both air and water surfaces.
How Well Can Sea Otters Hear Above The Water?
Sea otters have a hearing frequency of 125 to 32,000 Hz. Frequency, expressed in Hertz (Hz), measures how many sound waves or vibrations are in a second. High-frequency sounds are high-pitch tones, whereas low-frequency sounds are low-pitch, bassy sounds.
This range means they can detect a broad range of airborne sounds above the water surface. These sounds come in different forms, such as music, engine noise, and speech.
In aquariums and marine facilities, captive and rescued sea otters can hear and identify their trainer’s voices very well above the water. Their keen sense of hearing also allows them to respond to their own given names!
How Do Sea Otters’ Hearing Compare To Their Fellow Mustelids?
The otters commonly mistaken for sea otters have the same upper hearing frequency limit as them. North American River Otters, or river otters, can hear up to 32,000 Hz like sea otters!
But other terrestrial members of the Mustelidae family, like the domestic ferret (44,000 Hz) and the least weasel (51,000 Hz), have broader hearing sensitivity ranges than sea otters.
Although there is quite a difference between a sea otter’s hearing range and the other terrestrial mustelids, scientists still find their numbers comparable to one another.
In their research, biologists concluded that sea otters had retained an acute aerial hearing sensitivity that terrestrial carnivores have, despite spending most of their lives in the water.
How Do Sea Otters’ Hearing Compare To Humans?
In another anatomical study, researchers discovered that the sea otters’ inner ears look the same as other placental mammals or eutherians. Mothers that belong to this group all bear live young that get food and nourishment through their moms’ placenta while in the womb.
Over 4,000 animals belong to this group, including humans!
Like human beings, the inner ears of a sea otter appear similar to their fellow placental mammals:
- The cochlea is the spiraling, snail-like structure that you might remember seeing in your science textbooks. More importantly, it is the mammal’s hearing organ in the body.
- Inside the cochlea, you can find the sensitive organ of Corti. You can think of this structure as the body’s microphone because it lets us perceive the pitch and loudness of a sound.
With the help of the organ of Corti’s hair cells, the sound vibrations can be translated into neural signals which the brain can then interpret. And this is the only time that we can hear a sound.
Humans actually have a hearing range of 20 to 20,000 Hz. These numbers are pretty close to the sea otters’ 125 to 32,000 Hz, which isn’t surprising because of their nearly identical inner ear structures.
Yet humans can hear lower frequencies or deeper sounds than sea otters. Hearing much lower frequencies would’ve helped the sea otters avoid and survive many threats to their decreasing numbers like humans hunting them for their fur.
In contrast, sea otters are much more sensitive to higher frequencies than humans. This is beneficial for sea otter mums and pups as scream vocalization frequencies between them are highly variable. They can even reach up to 60,000 Hz!
Here is a table summarizing the aerial hearing frequencies of the mentioned mammals:
|Mammal||Hearing Range/Upper Limit|
|Sea Otter||125 to 32,000 Hz|
|River Otter||32,000 Hz|
|Domestic Ferret||44,000 Hz|
|Least Weasel||51,000 Hz|
|Humans||20 to 20,000 Hz|
Can Sea Otters Hear Well Underwater Too?
Unfortunately, sea otters can’t hear well underwater. Their best sensitivity range is just 4,000 to 23,000 Hz. It probably is one of the reasons why they only go for short, less than 5-minute dives in shallow waters.
As mentioned earlier, a sea otter’s ears aren’t that well-developed for a fully aquatic environment because they retained terrestrial inner ears. And sound travels 4 to 5X faster through water than air, making it more difficult for their ears to adjust.
Sea otters also like to spend most of their lives floating on their backs on the water’s surface. Since they can’t hear well underwater, perhaps they thought it would be better for them to watch out for predators from above the water.
While floating reclined on their backs, they can immediately hear lurking or approaching predators like bald eagles and killer whales.
How Important Is Hearing To A Sea Otter?
Speaking of killer whales…
Hearing is very important for sea otters to avoid predators.
In fact, most scientists believe that the sea otter’s sense of hearing is more useful in sensing dangers (like predators) than their sense of smell.
Interestingly, sea otters generally emit vocalizations ranging from 1,000 to 4,000 Hz below the water surface. So now you might wonder why the sea otter needed a 4,000 to 23,000 Hz underwater hearing range. They could’ve understood and communicated with one another with less than 4,000 Hz, right?
Thankfully, their ears accommodated a wider hearing range underwater because they wouldn’t have had a way to escape their top predator!
A killer whale’s whistles can be anywhere from 500 to 40,000 Hz. While killer whales still have a broader hearing range, the sea otters’ limited sense of hearing still gives them a fighting chance:
Do Sea Otters Actually Have Ears?
Yes, sea otters have a pair of small ears that are almost hidden in their fur.
Their fluffy faces might conceal them sometimes, but their external ears are visible once you get close enough to spot them on your own.
A sea otter’s ears also closely resemble a sea lion’s flappy, protruding ears (otariid).
Why Are Sea Otters’ Ears So Small?
The sea otters’ coffee-bean-shaped and sized ears are a mammalian adaptation of thermoregulation or keeping their bodies warm despite their cold environment.
Sea otters as well as polar bears are marine fissipeds. They are “split-footed” mammals:
- The sea otters’ forepaws are unwebbed and the digits are therefore separated, unlike their flipper-like feet.
- All of the polar bears’ five-toed paws or feet are only partially webbed, thus the toes are still relatively separated from each other.
Both of them are evolutionary newcomers to the marine environment. Sea otters and polar bears look and are actually more closely related to their terrestrial cousins (weasels and bears, respectively).
As a result, they lack many adaptations that pinnipeds (seals, sea lions, walruses) and cetaceans (dolphins and whales) already have.
Fortunately, sea otters and polar bears have small ears that help them to conserve their body heat while living in the cold. Because of their small size, their ears help retain their body heat and prevent their bodies from losing body heat too fast.
Sea Otters Can Close Their Ears Underwater
Sea otters can effortlessly fold their ears downward before going underwater. This helps them to prevent water from going into their ears. Like humans, water entering their ears could be harmful to sea otters and can even be the perfect, moist environment for bacterial or fungal growth.
Aside from not getting water into their tiny ears, sea otters can create less drag force by making sure that their ears are folded close to their heads when swimming. This allows them to swim and move faster in the water, just like how they tuck their forepaws when swimming or diving.
Hello! My name is Graciola Galo, but my friends call me “Gra” – so can you! Aside from being a dog lover, my bachelor’s degree in biology has helped me develop a deep appreciation for animals. I look forward to learning more about all kinds of wildlife in every future article I write for Floofmania and I aspire to impart that same awe and wonder to you, too!