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Wild Things

The weird and wonderful in the natural world

Sarah Zielinski

Wild Things

Wild Things

Why create a model of mammal defecation? Because everyone poops

kitten in a litterbox

Mammals with cylindrical feces — like cats and humans — tend to take about the same amount of time to poop, no matter their size, a new study reports.

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An elephant may be hundreds of times larger than a cat, but when it comes to pooping, it doesn’t take the elephant hundreds of times longer to heed nature’s call. In fact, both animals will probably get the job done in less than 30 seconds, a new study finds.

Humans would probably fit in that time frame too, says Patricia Yang, a mechanical engineering graduate student at the Georgia Institute of Technology in Atlanta. That’s because elephants, cats and people all excrete cylindrical poop. The size of all those animals varies, but so does the thickness of the mucus lining in each animal’s large intestine, so no matter the mammal, everything takes about the same time — an average of 12 seconds — to come out, Yang and her colleagues conclude April 25 in Soft Matter.

But the average poop time is not the real takeaway here (though it will make a fabulous answer to a question on Jeopardy one day). Previous studies on defecation have largely come from the world of medical research. “We roughly know how it happened, but not the physics of it,” says Yang.

Looking more closely at those physical properties could prove useful in a number of ways. For example, rats are often good models for humans in disease research, but they aren’t when it comes to pooping because rats are pellet poopers. (They’re not good models for human urination, either, because their pee comes out differently than ours, in high-speed droplets instead of a stream.)

Also, since the thickness of the mucus lining is dependent on animal size, it would be better to find a more human-sized stand-in. Such work could help researchers find new treatments for constipation and diarrhea, in which the mucus lining plays a key role, the researchers note.

Animal defecation may seem like an odd topic for a mechanical engineer to take on, but Yang notes that the principles of fluid dynamics apply inside the body and out. Her previous research includes a study on animal urination, finding that, as with pooping, the time it takes for mammals to pee also falls within a small window. (The research won her group an Ig Nobel Prize in 2015.)

And while many would find this kind of research disgusting, Yang does not. “Working with poop is not that bad, to be honest,” she says. “It’s not that smelly.” Plus, she gets to go to the zoo and aquarium for her research rather than be stuck in the lab.

But the research does involve a lot of poop — and watching it fall. For the study, the researchers timed the how long it took for animals to defecate and calculated the velocity of the feces of 11 species. They filmed dogs at a park and elephants, giant pandas and warthogs at Zoo Atlanta. They also dug up 19 YouTube videos of mammals defecating. Surprisingly, there are a lot of those videos available, though not many were actually good for the research. “We wanted a complete event, from beginning to end,” Yang notes. Apparently not everyone interested in pooping animals bothers to capture a feces’ full fall.

The researchers also examined feces from dozens of mammal species. (They fall into two classes: Carnivores defecate “sinkers,” since their feces are full of heavy indigestible ingredients like fur and bones. Herbivores defecate less-dense “floaters.”) And they considered the thickness and viscosity of the mucus that lines mammals’ intestines and helps everything move along as well the rectal pressure that pushes the material. All this information went into a mathematical model of mammal defecation — which revealed the importance of the mucus lining.

Yang isn’t done with this line of research. The model she and her colleagues created applies only to mammals that poop like we do. There’s still the pellet poopers, like rats and rabbits, and wombats, whose feces look like rounded cubes. “I would like to complete the whole set,” she says. And, “if you’ve got a good team, it’s fun.”

Animals,, Evolution

The weird mating habits of daddy longlegs

By Sarah Zielinski 11:00am, August 22, 2016
Scientists studying the sex lives of daddy longlegs are finding there’s a lot of diversity among this group of arachnids.

Lizard mom’s microbiome may protect her eggs

By Sarah Zielinski 5:19pm, August 16, 2016
Striped plateau lizard moms don’t do any parenting beyond laying eggs. But they may convey protection from pathogens with help from their microbiome.
Animals,, Ecology

Capybaras may be poised to be Florida’s next invasive rodent

By Sarah Zielinski 11:30am, August 12, 2016
Some capybaras have escaped their owners in Florida. Others have been set loose. Now there are fears the giant rodents could become established in the state.

Bird-friendly yards have a major downside — for birds

By Sarah Zielinski 7:00am, August 3, 2016
Vegetation and feeders bring birds into our yards. But those lures also bring more birds to collide with the windows in our homes.
Animals,, Oceans

Pup kidnapping has a happy ending when a seal gets two moms

By Sarah Zielinski 12:48pm, July 29, 2016
A female fur seal kidnapped another seal’s pup. But this turned out to be a positive the young seal, scientists found.
Oceans,, Ecology

Sea ice algae drive the Arctic food web

By Sarah Zielinski 1:00pm, July 26, 2016
Even organisms that don’t depend on sea ice depend on sea ice algae, a new study finds. But Arctic sea ice is disappearing.

Tiny ants move a ton of soil

By Sarah Zielinski 9:00am, July 20, 2016
For the first time, scientists have quantified how much soil ants move underground.
Animals,, Evolution

For jaguars, armored prey is no obstacle

By Sarah Zielinski 9:00am, July 15, 2016
With big heads, thick teeth and strong muscles, jaguars have evolved to take on dangerous prey, often animals covered with thick armor.

When bird populations shrink, females fly away

By Sarah Zielinski 7:41am, July 13, 2016
In small and shrinking populations of willow warblers, males outnumber females. That’s because girls choose to join bigger groups, a new study finds.

Beetles that battle make better moms than ones that never fight

By Sarah Zielinski 3:19pm, July 11, 2016
Female burying beetles that have to fight before reproducing spend more time caring for offspring than beetles with no fighting experience, a new study finds.
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