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The Mystery of the Sloth Poop

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
Pigeons Are Secretly Brilliant Birds That Understand Space and Time, Study Finds
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Of all the birds in the world, the pigeon draws the most ire. Despite their reputation as brainless “rats with wings,” though, they’re actually pretty brilliant (and beautiful) animals. A new study adds more evidence that the family of birds known as pigeons are some of the smartest birds around, as Quartz alerts us.

In addition to being able to distinguish English vocabulary from nonsense words, spot cancer, and tell a Monet from a Picasso, pigeons can understand abstract concepts like space and time, according to the new study published in Current Biology. Their brains just do it in a slightly different way than humans’ do.

Researchers at the University of Iowa set up an experiment where they showed pigeons a computer screen featuring a static horizontal line. The birds were supposed to evaluate the length of the line (either 6 centimeters or 24 centimeters) or the amount of time they saw it (either 2 or 8 seconds). The birds perceived "the longer lines to have longer duration, and lines longer in duration to also be longer in length," according to a press release. This suggests that the concepts are processed in the same region of the brain—as they are in the brains of humans and other primates.

But that abstract thinking doesn’t occur in the same way in bird brains as it does in ours. In humans, perceiving space and time is linked to a region of the brain called the parietal cortex, which the pigeon brains lack entirely. So their brains have to have some other way of processing the concepts.

The study didn’t determine how, exactly, pigeons achieve this cognitive feat, but it’s clear that some other aspect of the central nervous system must be controlling it. That also opens up the possibility that other non-mammal animals can perceive space and time, too, expanding how we think of other animals’ cognitive capabilities.

[h/t Quartz]

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The Queen's Racing Pigeons Are in Danger, Due to an Increase in Peregrine Falcons
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Queen Elizabeth is famous for her love of corgis and horses, but her pet pigeons don't get as much press. The monarch owns nearly 200 racing pigeons, which she houses in a luxury loft at her country estate, Sandringham House, in Norfolk, England. But thanks to a recent boom in the region’s peregrine falcon population, the Queen’s swift birds may no longer be able to safely soar around the countryside, according to The Telegraph.

Once endangered, recent conservation efforts have boosted the peregrine falcon’s numbers. In certain parts of England, like Norfolk and the city of Salisbury in Wiltshire, the creatures can even find shelter inside boxes installed at local churches and cathedrals, which are designed to protect potential eggs.

There’s just one problem: Peregrine falcons are birds of prey, and local pigeon racers claim these nesting nooks are located along racing routes. Due to this unfortunate coincidence, some pigeons are failing to return to their owners.

Pigeon racing enthusiasts are upset, but Richard Salt of Salisbury Cathedral says it's simply a case of nature taking its course. "It's all just part of the natural process,” Salt told The Telegraph. "The peregrines came here on their own account—we didn't put a sign out saying 'room for peregrines to let.' Obviously we feel quite sorry for the pigeons, but the peregrines would be there anyway."

In the meantime, the Queen might want to keep a close eye on her birds (or hire someone who will), or consider taking advantage of Sandringham House's vast open spaces for a little indoor fly-time.

[h/t The Telegraph]

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