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Universal Images Group via Getty Images

The Sound of Running Water Puts Beavers in the Mood to Build

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Universal Images Group via Getty Images

From the outside, a beaver dam looks like a heap of sticks, but a closer look reveals the insane amount of effort and detail that goes into building each structure. At a rate of five feet per day, beavers use mud, sticks, and rocks to construct the multi-chamber, watertight dams that hold their families and store their food. 

In the 1960s, Swedish biologist Lars Wilsson wanted to know if this industrious behavior was learned or innate. He decided to capture four adult beavers with the intention of raising them in different habitats. Some were kept in an outdoor enclosure and others in a glass-walled terrarium indoors. 

When a new generation of beavers was born, he chose a few of them to raise in isolation in order to study which of their behaviors were instinctual. He discovered that when released into running water, the young beavers built near perfect examples of dams on their first try. Wilsson then tried a different experiment where he placed the beavers in still or very slow-moving water. The subjects responded by burying themselves in the mud and making no attempts to build. 

It was only when Wilsson played them the sounds of running water through a speaker that their instincts kicked in. Suddenly the beavers were compelled to start building over the speaker, convinced that it was the source of the leak. When the sound was played for them through a loudspeaker on concrete, the beavers still built their dam over the dry floor. Even when presented with a clear pipe that showed water (silently) escaping through their dam and a speaker that played them the sound of running water, they chose to build over the speaker and ignore the clearly visible leak. 

This instinctive quirk makes beavers easy for people to manipulate. Instead of demolishing the dams that overflow river banks and damage property, a special, silent outflow pipe can be installed that diverts the water under the beavers’ radar. If blocking the sound of the pipe is impossible, people will sometimes make small holes in the dam around the pipe, which the beavers will innately plug up instead. For some reason, all those wicked dam-building skills now seem a lot less intimidating. 

[h/t: io9]

Watch a School of Humpback Whales 'Fish' Using Nets Made of Bubbles 

Just like humans, humpback whales catch many fish at once by using nets—but instead of being woven from fibers, their nets are made of bubbles.

Unique to humpbacks, the behavior known as bubble-net feeding was recently captured in a dramatic drone video that was created by GoPro and spotted by Smithsonian. The footage features a school of whales swimming off Maskelyne Island in British Columbia, Canada, in pursuit of food. The whales dive down, and a large circle of bubbles forms on the water's surface. Then, the marine mammals burst into the air, like circus animals jumping through a ring, and appear to swallow their meal.

The video offers a phenomenal aerial view of the feeding whales, but it only captures part of the underwater ritual. It begins with the group's leader, who locates schools of fish and krill and homes in on them. Then, it spirals to the water's surface while expelling air from its blowhole. This action creates the bubble ring, which works like a net to contain the prey.

Another whale emits a loud "trumpeting feeding call," which may stun and frighten the fish into forming tighter schools. Then, the rest of the whales herd the fish upwards and burst forth from the water, their mouths open wide to receive the fruits of their labor.

Watch the intricate—and beautiful—feeding process below:

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Big Questions
Why Do Dogs Love to Dig?
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Dog owners with green thumbs beware: It's likely just a matter of time before Fido turns your azalea bed into a graveyard of forgotten chew toys. When dogs aren't digging up your prized garden, they can be found digging elsewhere in your yard, at the beach, and even between your couch cushions at home. But what exactly is behind your dog's drive to turn every soft surface he or she sees into an excavation site?

According to Dr. Emma Grigg, an animal behaviorist and co-author of The Science Behind a Happy Dog, this behavior is completely normal. "When people say 'why do dogs dig,' the first thing that always comes to mind is 'well, because they're dogs,'" she tells Mental Floss. The instinct first appeared in dogs' wolf ancestors, then it was amplified in certain breeds through artificial selection. That's why dogs that were bred to hunt rodents, like beagles and terriers, are especially compelled to dig in places where such animals might make their homes.

But this tendency isn't limited to just a few specific breeds. No matter their original roles, dogs of all breeds have been known to kick up some dirt on occasion. Beyond predatory urges, Dr. Grigg says there are two main reasons a dog may want to dig. The first is to cool off on a hot day. When stuck on an open lawn with little to no shade, unearthing a fresh layer of dirt untouched by the sun is a quick way to beat the heat.

The second reason is to stash away goodies. Imagine your dog gets bored with chewing his favorite bone but knows he wants to come back for it later. Instead of leaving it out in the open where anyone can snatch it up, he decides to bury it in a secret place where only he'll be able to find it. Whether or not he'll actually go back for it is a different story. "There's a disconnect with modern dogs: They know the burying part but they don't always know to dig it up," Dr. Grigg says.

Because digging is part of a dog's DNA, punishing your pet for doing so isn't super effective. But that doesn't mean you should stand idly by as your yard gets turned inside-out. When faced with this behavior in your own dog, one option is to redirect it. This can mean allowing him to dig in a designated corner of the yard while keeping other parts off-limits, or setting up a raised flowerbed or sandbox especially to satisfy that urge. "You can get him interested in the area by burying a couple bones or some interesting things in there for him to dig," Dr. Grigg says. "I like the idea of buried treasure."

If your dog's motive for digging is more destructive than practical, he may have an energy problem. Dogs require a certain amount of stimulation each day, and when their humans don't provide it for them they find their own ways to occupy themselves. Sometimes it's by chewing up shoes, toppling trash cans, or digging ditches the perfect size for twisting ankles. Fortunately, this is nothing more walks and playtime can't improve.

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