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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These Sparrows Have Been Singing the Same Songs for 1500 Years
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Swamp sparrows are creatures of habit—so much so that they’ve been chirping out the same few tunes for more than 1500 years, Science magazine reports.

These findings, published in the journal Nature Communications, resulted from an analysis of the songs of 615 adult male swamp sparrows found in six different areas of the northeastern U.S. Researchers learned that young swamp sparrows pick up these songs from the adults around them and are able to mimic the notes with astounding accuracy.

Here’s what one of their songs sounds like:

“We were able to show that swamp sparrows very rarely make mistakes when they learn their songs, and they don't just learn songs at random; they pick up commoner songs rather than rarer songs,” Robert Lachlan, a biologist at London’s Queen Mary University and the study’s lead author, tells National Geographic.

Put differently, the birds don’t mimic every song their elders crank out. Instead, they memorize the ones they hear most often, and scientists say this form of “conformist bias” was previously thought to be a uniquely human behavior.

Using acoustic analysis software, researchers broke down each individual note of the sparrows’ songs—160 different syllables in total—and discovered that only 2 percent of sparrows deviated from the norm. They then used a statistical method to determine how the songs would have evolved over time. With recordings from 2009 and the 1970s, they were able to estimate that the oldest swamp sparrow songs date back 1537 years on average.

The swamp sparrow’s dedication to accuracy sets the species apart from other songbirds, according to researchers. “Among songbirds, it is clear that some species of birds learn precisely, such as swamp sparrows, while others rarely learn all parts of a demonstrator’s song precisely,” they write.

According to the Audubon Guide to North American Birds, swamp sparrows are similar to other sparrows, like the Lincoln’s sparrow, song sparrow, and chipping sparrow. They’re frequently found in marshes throughout the Northeast and Midwest, as well as much of Canada. They’re known for their piercing call notes and may respond to birders who make loud squeaking sounds in their habitat.

[h/t Science magazine]

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5 Fascinating Facts About Koko the Gorilla
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ZUMA Press, Inc., Alamy

After 46 years of learning, making new friends, and challenging ideas about language, Koko the gorilla died in her sleep at her home at the Gorilla Foundation in Woodside, California on June 21, 2018. Koko first gained recognition in the late 1970s for her ability to use sign language, but it was her friendly personality that made her a beloved icon. Here are five facts you should know about the history-making ape.

1. SHE KNEW OVER 1000 SIGNS.

Francine "Penny" Patterson, then a graduate student at Stanford University, was looking for an animal subject for her inter-species animal communication experiment in the early 1970s when she found a baby gorilla at the San Francisco Zoo. Originally named Hanabiko (Japanese for "fireworks child," a reference to her Fourth of July birthdate), Koko took to signing quickly. Some of the first words Koko learned in "Gorilla Sign Language," Patterson's modified version of American Sign Language, were "food," "drink," and "more." She followed a similar trajectory as a human toddler, learning the bulk of her words between ages 2.5 and 4.5. Eventually Koko would come to know over 1000 signs and understand about 2000 words spoken to her in English. Though she never got a grasp on grammar or syntax, she was able to express complex ideas, like sadness when watching a sad movie and her desire to have a baby.

2. SHE CHANGED WHAT WE KNEW ABOUT LANGUAGE.

Not only did Koko use language to communicate—she also used it in a way that was once only thought possible in humans. Her caretakers have reported her signing about objects that weren't in the room, recalling memories, and even commenting on language itself. Her vocabulary was on par with that of a 3-year-old child.

3. SHE WASN'T THE ONLY APE WHO SIGNED.

Koko was the most famous great ape who knew sign language, but she wasn't alone. Michael, a male gorilla who lived with Koko at the Gorilla Foundation from 1976 until his death in 2000, learned over 500 signs with help from Koko and Patterson. He was even able to express the memory of his mother being killed by poachers when he was a baby. Other non-human primates have also shown they're capable of learning sign language, like Washoe the chimpanzee and Chantek the orangutan.

4. SHE HAD FAMOUS FRIENDS.

Koko received many visitors during her lifetime, including some celebrities. When Robin Williams came to her home in Woodside, California in 2001, the two bonded right away, with Williams tickling the gorilla and Koko trying on his glasses. But perhaps her most famous celebrity encounter came when Mr. Rogers paid her a visit in 1999. She immediately recognized him as the star of one of her favorite shows, Mister Rogers' Neighborhood, and greeted him by helping him take off his shoes like he did at the start of every episode.

5. SHE WAS A LOVING CAT MOM.

Koko was never able to have offspring of her own, but she did adopt several cats. After asking for a kitten, she was allowed to pick one from a litter for her birthday in 1985. She named the gray-and-white cat "All Ball" and handled it gently as if it were her real baby, even trying to nurse it. She had recently received two new kittens for her 44th birthday named Ms. Gray and Ms. Black.

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