Why Do Birds Poop And Pee At The Same Time?

I don’t know if my son was watching a nature program, or if he’d been talking about this at school, or what. All I know is that, as we were walking into the condo one day, he suddenly stops and points. “Look dad! An owl!”

I stare along the side of the building, wondering which of the trees he’s talking about. Or is it perched on a balcony, maybe? “I… don’t see it,” I say.

“It’s right there!” he exclaims, pointing. “Oh, no. It’s a squirrel. Look, dad! A squirrel!”

“I don’t see it,” I tell him. “But my eyes aren’t as good as yours.”

He nods at that. “Dad?”

“Yes, son?”

“Why do birds poop and pee at the same time?”

…that is not what I thought he was going to ask.

Do they poop and pee at the same time?

This seems like the first place to start, because I’m not at all certain they do. I mean, sure. I’ve heard this before. But it wouldn’t be the first time I’ve found that “received wisdom” is wrong and that something I thought was true wasn’t true. However, in this case, it seems that received wisdom is correct.

This is going to be more than I wanted to know, isn’t it?

Hey, you’re the one reading this.

Pretty much all animals produce ammonia (NH3) during digestion. It’s a side effect of the breakdown of proteins, which all animals need whether they’re carnivores or herbivores. Ammonia is, however, toxic (doses of 350 mg/kg of weight can kill), which means that animals have to deal with it in some fashion. And by “deal with” I mean “get rid of”.

Generally speaking, mammals will mix it with some of the waste carbon dioxide (CO2) they produce through breathing and convert it into urea (CO(NH3)2) – a far less toxic chemical (the lethal dose is 8,471 mg/kg) that also happens to be water soluble. Mammals then, generally speaking, expel it (along with other waste chemicals) in the form of urine.

Birds don’t do this. Birds, it seems, don’t even have bladders.

Sigh. Tell me more.

To start with, most birds convert ammonia into uric acid (C5H4N3O3, lethal dose around 5040 mg/kg) instead of urea. The other thing they do, which is the reason why they simultaneously poop and pee, has to do with anatomy. See, bird excretory systems work a lot like lizards. They have kidneys, of course, and ureters (the ducts that allow urine to leave the kidney). However, they lack bladders. Instead, they have something called a cloaca – a multipurpose organ that serves as both the reproductive and excretory organ.

The urine enters the cloaca through the ureters, where it is pushed up into the large intestine. The large intestine re-absorbs much of the water content, allowing the urine to be concentrated into a thick paste before it is passed by the bird. since uric acid dries white, this lends bird droppings their distinctive appearances.

So, in short, birds poop and pee at the same time because of evolution.  And because they aren’t equipped to poop and pee separately.


Where Does The Potty Go?

We’re out shopping, and my son announces – as small children are wont to do – that he needs “to go to the potty”. So I’m standing in the men’s room with him as he goes about his business, back to him as he finishes and flushes. And then he asks the title question: “where does the potty go?”

It hits me that I have, at best, an extremely vague idea. But I do my best. “Well, it goes through pipes into a sewer.”

“And then into the river?” he asks, lighting up. We’ve looked at storm water drains before, walking home form daycare.

“No,” I tell him. “It goes to a treatment plant. Like in Curious George.”

“Oh,” he responds. Then another thought strikes him. “How do they clean the pee out?”

Now I’m stumped. Stumped, and slightly grossed out. But curious.

How Does A Toilet Work?


I’ll be honest, here. When I searched for “how does a toilet work”, I never anticipated that I’d find myself on a web page hosted by the Massachusetts Institute of Technology. But they have a straight-forward article from a student titled How A Toilet Works, and it turns out to be all about siphons.  And physics.

Everyone understands that, when you pull the flush handle, water empties from the tank into the bowl. What happens next is based on the “trapway” in that diagram up there – the famous “u-bend”. The water level rises in the bowl, and because of the way water works that also causes the water level to rise in the trapway. This puts you in a position of having greater pressure in the bowl than in the air filling the trapway, and the water moves from the area of greater pressure to the area of lower pressure until the pressure equalizes.

What makes flushing especially interesting has to do with water velocity. See, as described in the Bernoulli Equation, fluids under constant pressure will move faster through narrow channels. That’s why you can spray water faster from a hose when you put your thumb over the opening – the velocity increases as you constrict the channel. Well, the trapway channel is significantly narrower than the mouth of the bowl. So, as water is pumped in, the bowl drains faster than it fills until the bowl is completely drained. Then the siphon effect breaks down and the bowl refills with clean (for “you still don’t want to drink that” values of “clean”) water.

John Harrington and his successors were pretty ingenious, weren’t they?

Once You’ve Flushed, Where Does It Go?

Once you’ve flushed, there are three primary places (in the United States, at least) that the waste water can go: into a septic drain field, into a septic tank, or into a sewer. Which one you use really depends on where you are, what sort of access you have to municipal water and sewer services, and local ordinances.

Septic drain fields are also known as leach fields or leach beds. They consist of “a network of perforated pipes that are laid in underground gravel-filled trenches to dissipate the effluent from a water-based collection and storage/treatment or (semi-)centralized treatment technology.” Basically, your waste water flows out the into the pipes, which should be buried deeply (the article mentions ten feet of soil). Wastewater leaks out of the pipes, with the water being absorbed and percolating downwards and the (I love this phrase) “organic materials” being consumed by bacteria and other microfauna.

The leach bed is a somewhat more sophisticated version of a soak pit, which is pretty much what it sounds like: a pit that receives wastes or wastewater and holds it as it soaks into the surrounding soil. If you see an old-fashioned outhouse, you’ve seen the surface component of a soak pit.

A septic tank is, quite literally, a big tank. YOur waste water empties into that tank, and then is emptied out and disposed of at a later date.

By no stretch of the imagination are these the only means of disposing of waste water. The SSWM (Sustainable Sanitation and Water Management) web site discusses several other techniques and technologies.

How Do You Clean It?

If you’ve got a leach bed or a soak pit or something similar, cleaning the waste water is relatively straight-forward. You let nature handle it, and you don’t dump toxic chemicals in your toilet while you do. However, if you’ve got something like a septic tank or a sewer hookup, then you turn to wastewater and sewage treatment plants. And according to the Wastewater treatment page on the Food and Agriculture Organization of the United Nations website, you’ve pretty much got two options for treatment: conventional treatment and natural biological treatment.

Conventional wastewater treatment is what you probably first think of when you hear about a “sewage plant”. It “consists of a combination of physical, chemical, and biological processes and operations to remove solids, organic matter and, sometimes, nutrients from wastewater,” and it generally goes through four stages with the imaginative names of preliminary, primary, secondary, and tertiary (or advanced).

  • Preliminary treatment removes “coarse solids and other large materials often found in raw wastewater”, generally through screens and filters designed to trap large objects (which, in this context, includes “grit”). water velocity is generally high in preliminary treatment to keep particulate solids from settling.
  • Primary treatment is “the removal of settleable organic and inorganic solids by sedimentation, and the removal of materials that will float (scum) by skimming. The goal is to remove 25% – 50% of the biochemical oxygen demand (the dissolved oxygen in water used by microorganisms to degrade and consume organic compounds), 50% – 70% of the suspended solids, and 65% of the oil and grease in the water. The resulting settled sludge is pumped out intermittently for processing in – wait for it – sludge processing units (generally by allowing it to be eaten by bacteria in an anaerobic process, allowing it to dry before processing further).
    • Once water has gone through primary treatment it is generally considered acceptable for wastewater irrigation, which can be used for all crops not intended for human consumption and some crops that are directly consumed by humans (orchards and vineyards, for instance).
  • Secondary treatment “follows primary treatment and involves the removal of biodegradable dissolved and colloidal organic matter using aerobic biological treatment processes”.  The process seems counter-intuitive after primary treatment, because microorganisms are added back to the water, along with more air, to consume more of the organic matter remaining in the water.  Further settling tanks (or sometimes rotating tanks) are then used to separate out the microorganisms in a process that removes 85% f the biochemical oxygen demand and suspended solids.
  • Tertiary treatment kicks in when there are specific contaminates that are not removed by the primary and secondary treatments.  They are many and varied, and depend on what contaminate or contaminates are to be removed.

Natural biological treatment often follows the same process as conventional treatment, but makes use of natural processes (such as evaporation) or plant life (such as algae or trees) to filter organic contaminates from the water.  The processes are generally slower than conventional treatment, but also tend to cost less to maintain and operate.

So, where does the potty go?  Out into our infrastructure, and eventually into the ecosystem.

Why does he have to poop?

Ah, kids. You have to love them.

We’ve all just gotten home, and my wife goes to take the dog out to – as they euphemistically say – ‘do his business’. My son goes over to the porch door, and asks what she’s doing. Bear in mind, of course, that he’s seen us take the dog out several times a day since he was born. But my wife, with her bounless patience, simply answers that he “has to go potty”.

My son looks at her. “Why does he have to poop?”

It’s actually a kind of fair question. Why do we? Wouldn’t it make more sense if we could metabolize everything? It sure would make more sense. Sadly, however, we don’t. And so, the things we don’t metabolize have to go somewhere. Or, at least, that’s how I assumed the process worked. And it was accurate, as far as it went. But it turns out there’s a little more to it than just that.

To start with, let’s recap the digestive process. The National Institute of Health has a pretty good one-page presentation titled Your Digestive system and How it Works. In brief, food goes into the mouth where your saliva begins breaking down starches. It then moves to the stomach, where your stomach acid begins breakind down proteins. From there the food and acid mix (called “chyme”) moves to the small intestine, where starches and proteins are further broken down along with carbohydrates and fats (thanks in part to pancreatic juices and bile), and where nutrients are absorbed into the blood. Whatever’s left is then dumped into the large intestine, which absorbs water and any remaining nutrients and then expels the remaining waste matter.  Voila! Poop! But… what is it? It’s all well and good to say it’s “waste matter”, but what does that mean?

I found two different sources, each of which agree in broad strokes on the composition of human stool. It is approximately:

  • 75% water
  • 7.5% bacteria
  • 2.5% – 5% “inorganic substance”
  • 2.5% – 5% fat
  • 0.5% – 0.75%
  • Undigested foods make up the remaining quantities

So why do dogs (or people, for that matter) poop? Because evolution gave us digestive systems that are good enough, not perfect. And because all chemical processes – and digestion is just another chemical process – leave waste behind. And because, eventually, we’d hit a point of diminishing returns. If nothing else, how much carbon does one body need?

What Eats Poop?

You just have to love the questions kids ask.

I’m eating dinner last night, and my son is watching Wild Kratts on PBS Kids. Normally, we have him sitting at the table with us for dinner. But I got home late, and so I’m pretty much eating by myself, and I’m not paying attention to the show. But then, he pipes up with a question. “When all of the animals go potty, what eats it?”

Well, I think to myself as I take a bite of my calzone, that came out of nowhere. So I wrack my brain. “Uhm… bugs?”

“No, daddy!” he declares. “Porcupines!”

Honestly? I’ve got no idea here.  Bugs.  I’m pretty sure bugs eat dung.  I’ve got no idea about porcupines.  Maybe the Wild Kratts taught him a valuable life lesson about mammalian poop consumption. I don’t know. But, when you get right down to it, that’s the point of this blog. So, brace yourselves as we start off with your new word of the day: Coprophagia.

According to Dictionary.com, cophropagia is the noun version of the adjective “coprophagous”, meaning “feeding on dung, as certain beetles”. And, from what I can find, it’s common not just in beetles and other invertebrates, but among mammals as well. Young herbivorous mammals use it as a way to obtain the starters for the gut bacteria that help them digest vegetation (cellulose doesn’t digest easily). The dung of herbivores also contains a significant quantity of semi-digested plant matter, so many herbivores will eat (re-eat?) it to gain greater access to any nutrients still contained in the waste. Heck, it turns out that even our close cousins – gorillas and chimpanzees – engage in this behavior.

In humans, coprophagia is considered a symptom of a few different mental illnesses. But that’s a comparatively recent development. As recently as the 18th century, a juice derived from boiled cow or sheep dung was used as cough syrup in the United States. And even now, although doctors strongly recommend that you do not consume poop, there is a thing called bacteriotherapy () (also known as fecal transplantation), which is used to replenish gut bacteria in humans who have been through significant antibiotic treatments.

But, back to my son’s point, what about the porcupines?  Well, according to The North American Porcupine Second Edition, by Uldis Roze:

Unlike rabbits and beavers, who also have large caeca, the porcupine is not normally coprophagous (it does not re-ingest feces for a second round of nutrient extraction). That means that the bacteria in the caecum are not themselves used as food sources. The porcupine’s relatively long large intestine, which serves to absorb the fermentation products, partially compensates.
page 47

Dr. Uldis Roze is a Professor Emeritus, in the Department of Biology, Queens College at the City University of New York.  According to his web site, he’s “interested in the anatomy, ecology, and natural history of the North American porcupine”.  Quite literally, he wrote the book on the subject.  So if he says they aren’t normally coprophagous I’ll assume he knows what he’s talking about.

Aren’t you glad you read this entry?