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Frogs Use Storm Drains for Better Mating Calls

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As humans take up ever more space and urbanize the untamed wilderness, the animals that call these places home have a tough choice to make: move on to someplace else or adapt to their new surroundings.

Staying put can be especially tricky for animals that rely on sound to communicate with each other and steer clear of danger. Brick walls and human-made noise can change the acoustic landscape and drown out their mating calls or mask the sounds of approaching predators. In Taiwan, plucky little frogs are making the most of things. Instead of letting human infrastructure get in their way, they’re putting it to use. 

In suburban and rural areas of Taiwan, it’s pretty easy to find open concrete drains alongside roads and foot paths. Their bottoms are often caked in mud and covered in plant litter. This makes them attractive to small animals as travelways, mating sites, and even living space. But the concrete walls can make conversation difficult by causing sounds to ricochet and echo. Animals listening for each other's calls “will hear not just the direct sound wave, but also reflected waves arriving at different times,” say a team of researchers at National Taiwan University in Taipei.

But there’s an upside to that, depending on who’s doing the talking. “In contrast, some signals (e.g., those with narrow frequency bandwidths) can potentially benefit from reverberations,” the researchers say in a new paper. “The reflected sound waves can make the signal higher in amplitude and longer.” Mientien tree frogs seem to have figured this out, and the males are often found perched in the drains letting out their high pitched mating calls to attract females. 

When the team compared the calls of the frogs in the drains with those that sat next to them on the ground, they found that the drain calls were louder and longer. The echoes caused by the concrete didn’t degrade the calls. Instead, the researchers say, the drains acted like “miniature urban canyons” and actually amplified the narrow-bandwidth calls.

While the researchers didn’t look at how female frogs responded to the calls in this study, they suspect that the drain-aided calls are just what they want to hear. Other research has shown that female frogs and other amphibians are more attracted to long, loud calls. 

Hanging out in drains isn’t all fun and frog flirting, though. It also presents some challenges. The first is that the shape of the drains and the shelter they provide attracts snakes that can hide in the muck and ambush unwary prey. Many of the frogs seem to get around this by perching on branches leaning against the drain walls so they’ve got a good view of their surroundings. 

Another problem is that the steep concrete walls can be difficult to maneuver. Mientien tree frog mating involves the female carrying the male away from his calling perch to a damp place to reproduce, and the females might have a hard time hauling the males out of the drain. Whether that leads a lot of females to abandon males in the drains without mating or even ignore drain callers in the first place remains to be seen. For now, at least, the drain-as-megaphone looks like a clever workaround for tree frogs looking for love. 

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Big Questions
Why Do Cats Freak Out After Pooping?
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Cats often exhibit some very peculiar behavior, from getting into deadly combat situations with their own tail to pouncing on unsuspecting humans. Among their most curious habits: running from their litter box like a greyhound after moving their bowels. Are they running from their own fecal matter? Has waste elimination prompted a sense of euphoria?

Experts—if anyone is said to qualify as an expert in post-poop moods—aren’t exactly sure, but they’ve presented a number of entertaining theories. From a biological standpoint, some animal behaviorists suspect that a cat bolting after a deposit might stem from fears that a predator could track them based on the smell of their waste. But researchers are quick to note that they haven’t observed cats run from their BMs in the wild.

Biology also has a little bit to do with another theory, which postulates that cats used to getting their rear ends licked by their mother after defecating as kittens are showing off their independence by sprinting away, their butts having taken on self-cleaning properties in adulthood.

Not convinced? You might find another idea more plausible: Both humans and cats have a vagus nerve running from their brain stem. In both species, the nerve can be stimulated by defecation, leading to a pleasurable sensation and what some have labeled “poo-phoria,” or post-poop elation. In running, the cat may simply be working off excess energy brought on by stimulation of the nerve.

Less interesting is the notion that notoriously hygienic cats may simply want to shake off excess litter or fecal matter by running a 100-meter dash, or that a digestive problem has led to some discomfort they’re attempting to flee from. The fact is, so little research has been done in the field of pooping cat mania that there’s no universally accepted answer. Like so much of what makes cats tick, a definitive motivation will have to remain a mystery.

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

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Animals
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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