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5 Sounds You Probably Can't Hear

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Think you have perfect hearing? There are still plenty of sounds in the world that you can’t detect. The low range of human hearing starts around 20 hertz, and tops out at about 20,000 [PDF]. By contrast, bats can hear ultrasonic sounds with frequencies up to 110,000 hertz. Other animals, like elephants, hear sounds many times lower than those a human can perceive. And as people age, their hearing gets even worse, eliminating even more sounds from the range of audible noises. Here are just a few sounds most people are missing out on: 

1. Sounds for young people 

As humans age, their hearing changes. Age-related hearing loss, called presbycusis, means that older people can’t hear some high-pitched sounds they would have heard in their youth. Most people over the age of 18 cannot hear the 17,400 hertz tone in the video above. 

2. Music designed for cats

In 2014, activists from Pussy Riot rigged an electric piano to play music designed specifically for cats. Cats possess ultrasonic hearing, meaning they can hear a much wider frequency of sounds than humans (or most other mammals, for that matter) can [PDF]. Although people could hear portions of the concerto Pussy Riot staged to protest Internet censorship, the melody is a whole lot more complex from the feline point of view. For what it's worth, the cats seemed to enjoy it. Research has shown that cats are pretty into feline-specific tunes, in general. (We have some video evidence.) 

3. A dog-specific Beatles’ song

In the Beatles’ song “A Day in the Life,” the band included a whistling noise at a frequency of 15,000 hertz right after the last chord of the song, designed to be heard by canine Beatles fans. “We’d talk for hours about these frequencies below the sub that you couldn’t really hear and the high frequencies that only dogs could hear. We put a sound on Sgt. Pepper that only dogs could hear,” Paul McCartney told the BBC in 2013. (The sound starts just after the 5-minute mark.)

4. Ultrasonic finger friction

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When you gently rub your thumb and index finger together, the friction creates an ultrasonic signal [PDF]. The action is a useful way to test out the function of a bat detector, which converts ultrasonic sound from bat echolocation into noise humans can hear. In the book Insects Through the Seasons, entomologist Gilbert Waldbauer writes that pet bats can be trained to respond to the sound, and fly toward it. 

5. Infrasonic elephant calls 

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Elephants can hear and make sounds well below human range, to as low as 14 to 16 hertz. They can also produce these infrasonic calls at extremely high volumes, around 85 to 95 decibels. For comparison purposes, 95 decibels is the equivalent of the noise of a subway train from 200 feet away. These loud, low sounds allow elephants to keep in touch with each other over distances of more than a mile. Listen to an example of these elephant rumbles from the Elephant Listening Project

See Also: 9 Strange Sounds No One Can Explain

[h/t: reddit

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Whale Sharks Can Live for More Than a Century, Study Finds
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Some whale sharks alive today have been swimming around since the Gilded Age. The animals—the largest fish in the ocean—can live as long as 130 years, according to a new study in the journal Marine and Freshwater Research. To give you an idea of how long that is, in 1888, Grover Cleveland was finishing up his first presidential term, Thomas Edison had just started selling his first light bulbs, and the U.S. only had 38 states.

To determine whale sharks' longevity, researchers from the Nova Southeastern University in Florida and the Maldives Whale Shark Research Program tracked male sharks around South Ari Atoll in the Maldives over the course of 10 years, calculating their sizes as they came back to the area over and over again. The scientists identified sharks that returned to the atoll every few years by their distinctive spot patterns, estimating their body lengths with lasers, tape, and visually to try to get the most accurate idea of their sizes.

Using these measurements and data on whale shark growth patterns, the researchers were able to determine that male whale sharks tend to reach maturity around 25 years old and live until they’re about 130 years old. During those decades, they reach an average length of 61.7 feet—about as long as a bowling lane.

While whale sharks are known as gentle giants, they’re difficult to study, and scientists still don’t know a ton about them. They’re considered endangered, making any information we can gather about them important. And this is the first time scientists have been able to accurately measure live, swimming whale sharks.

“Up to now, such aging and growth research has required obtaining vertebrae from dead whale sharks and counting growth rings, analogous to counting tree rings, to determine age,” first author Cameron Perry said in a press statement. ”Our work shows that we can obtain age and growth information without relying on dead sharks captured in fisheries. That is a big deal.”

Though whale sharks appear to be quite long-lived, their lifespan is short compared to the Greenland shark's—in 2016, researchers reported they may live for 400 years. 

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Animal Welfare Groups Are Building a Database of Every Cat in Washington, D.C.
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There are a lot of cats in Washington, D.C. They live in parks, backyards, side streets, and people's homes. Exactly how many there are is the question a new conservation project wants to answer. DC Cat Count, a collaboration between Humane Rescue Alliance, the Humane Society, PetSmart Charities, and the Smithsonian Conservation Biology Institute, aims to tally every cat in the city—even house pets, The New York Times reports.

Cities tend to support thriving feral cat populations, and that's a problem for animal conservationists. If a feline is born and grows up without human contact, it will never be a suitable house cat. The only options animal control officials have are to euthanize strays or trap and sterilize them, and release them back where they were found. If neither action is taken, it's the smaller animals that belong in the wild who suffer. Cats are invasive predators, and each year they kill billions of birds in the U.S. alone.

Before animal welfare experts and wildlife scientists can tackle this problem, they need to understand how big it is. Over the next three years, DC Cat Count will use various methods to track D.C.'s cats and build a feline database for the city. Sixty outdoor camera traps will capture images of passing cats, relying on infrared technology to sense them most of the time.

Citizens are being asked to help as well. An app is currently being developed that will allow users to snap photos of any cats they see, including their own pets. The team also plans to study the different ways these cats interact with their environments, like how much time pets spend indoors versus outdoors, for example. The initiative has a $1.5 million budget to spend on collecting data.

By the end of the project, the team hopes to have the tools both conservationists and animal welfare groups need to better control the local cat population.

Lisa LaFontaine, president and CEO of the Humane Rescue Alliance, said in a statement, “The reality is that those in the fields of welfare, ecology, conservation, and sheltering have a common long-term goal of fewer free-roaming cats on the landscape. This joint effort will provide scientific management programs to help achieve that goal, locally and nationally."

[h/t The New York Times]

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