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The Mystery of the Sloth Poop

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Three-toed sloths are just that: three-toed, and slothful. They live high in the tree canopy and feed exclusively on the foliage there, hanging around most of the time and moving slowly when they move at all. 

They only descend from their leafy home once a week to make a bathroom run. After shimmying down the trunk of a tree, a sloth digs a small hole in the dirt, poops in it, covers their makeshift toilet with leaves, and then climbs back up. This is not the most efficient way to poop, nor the safest. Climbing down a tree to ground level and then back can cost a sloth as much as 8 percent of its daily calorie intake, and the animals are out of their element and incredibly vulnerable on the ground—more than half of all recorded sloth deaths are caused by attacks from predators at or near the ground. 

If a simple poop can cost a sloth its life, why do it like that? The three-toed sloth’s cousin, the two-toed sloth, simply defecates from the canopy. It can’t be pleasant to be standing underneath one when that happens, but the sloths are safer for it. If three-toed sloths keep making these costly and risky trips to a ground-floor bathroom, there must be something that makes the trip worth it. 

Scientists have come up with a few possible benefits for ground-pooping, like fertilizing the trees that the sloths call home or revealing their locations to other sloths so they can mate (how romantic). Ecologist Jonathan Pauli and other researchers from Wisconsin and Virginia have a different idea, though, that’s rooted in the sloth’s dietary problems. 

Sloths are among the 0.02 percent of mammals that are specialized arboreal herbivores, living in trees and foraging for food there. This lifestyle isn’t an easy one. To live on a tree branch, you have to be relatively small and light, but a limit on body size also puts a limit on how much you can digest. A sloth’s main source of food, leaves, is pretty nutrient-poor and not easy to digest to begin with, so they’re under some serious nutritional constraints. Pauli and his team wondered if, when sloths went downstairs to use the bathroom, they were also grabbing some extra food. 

The key here is the miniature zoo that sloths carry around with them. Their thick fur is home to all kinds of algae, fungi, arachnids and insects. Among these tenants are moths from the genus Cryptoses, commonly (and adorably) called “sloth moths.” These moths are absolutely dependent on their host sloth’s weekly bathroom trip. The females lay their eggs in the sloth dung, which the larva then live off of until they become adults and can fly upward to move onto their own sloth. Maybe the sloths are just as dependent on the moths, and aid their lifecycle because the bugs are somehow nutritionally important. 

The researchers took locks of hair from the ground-pooping brown-throated three-toed sloth and from Hoffmann’s two-toed sloth, which prefers a “bombs away” style of defecation. After removing and counting the moths from each hair sample, they looked at the nutrients available in the hair and then compared them to some sloth stomach contents to see if there was any connection between the moths, the contents of the hair, and what the sloth had been eating.

They found that sloths that had more moths on them also had more nitrogen-rich hair and more algae growth. The algae also turned up in the sloths’ stomachs, and when the researchers analyzed it they found that it was easily digestible and rich in carbs, proteins, and fats. 

So the perilous pooping process keeps the moths around. Moths mean more nitrogen (why, exactly, is still an open question—the moths might be dragging the nitrogen up from the sloth poop or releasing it when they die). More nitrogen promotes more algae. And algae seems to be a good nutritional supplement—though the researchers haven’t crunched the numbers to see just how much energy and nutrients the algae could provide. It’s a roundabout way to get a meal, but whatever works. Two-toed sloths, by the way, are less fussy eaters, and will forage a wider area, which may explain why they can poop from the canopy—they don’t need the moths or the algae that comes with them. 

There’s one big problem with all of this, according to other sloth researchers: There’s little evidence that the sloths are eating the algae from their hair. No one has seen them licking their fur or pawing at it in a way that suggests they’re picking the algae out for a snack. The study found bits of algae in sloth stomachs, but no one’s even sure if it's enough make any real nutritional impact. 

Becky Cliffe, a zoologist working at the Sloth Sanctuary of Costa Rica, doesn’t think the algal snacks are worth the risk of a climb down a tree, because sloths can get along fine without them. “For a start, sloths in captivity that are fed a natural diet but don’t have any algae are perfectly healthy,” she writes. “Blood analysis done at the Sloth Sanctuary shows no difference between these captive animals and their wild, algae-covered counterparts.”

Even if the sloths are chowing down on algae when no one is looking, it doesn’t seem to be so integral to their diet that they’d risk time on the ground. For now, the way a sloth poops remains one of the great mysteries of the rainforest. 

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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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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.

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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