When observing bird droppings, one of the first questions that typically comes to mind is, “Why is bird poop white?” So let’s talk about poop.
While most of us avoid “poop talk,” there is a time and place to get into this messy business. And for nature lovers and biologists, poop is quite fascinating. Mammal stool on the trail is a “whodunit?” mystery. Poop tells a story and offers a glimpse into the mysterious wild animals we share our lives with.
Bird poop also tells a story, but its story is different from that of other animals. While mammal poop can tell you which animal it was, bird poop tells the story of evolution and unique anatomy. This is why most bird poop looks the same among the many different species.
So why is bird poop white? In this blog, we’ll answer that question and dive into why birds have evolved to poop the way they do.
Why is Bird Poop White?
To answer the question, “Why is bird poop white?” we have to discuss how birds excrete nitrogenous waste products. In humans and mammals, excess nitrogen is converted to urea in the kidneys, which is water-soluble. We then excrete that as urine.
Birds don’t convert excess nitrogen to urea, but rather to uric acid, which has low solubility in water. In other words, it doesn’t dissolve or break down easily in water (depending on pH levels).
As such, birds evolved to pass uric acid as a more solid substance rather than as a liquid. The white paste we see in bird droppings is the uric acid, or what we could consider as their urine (though it’s not technically urine).
Because uric acid has low water solubility, it’s sometimes difficult to clean it off surfaces. That’s why when you try to clean bird poop off your windshield, it just smears all over the place. Luckily, it does dissolve in alkaline water. You can mix a simple cleaning solution of water, soap, and baking soda to help remove bird poop from your windshield.
Most bird droppings also have some brown mixed in with the white. This is fecal matter, or poop, which consists of fiber and other indigestible parts of the bird’s food. The reason they come out together as one substance is because birds expel their waste products through one opening: the cloaca, or vent.
One-Hole-Wonder: The Cloaca
Unlike mammals, birds only have one excretion hole, called the cloaca, or vent. This vent expels the uric acid, poop, and even eggs in females or sperm in males. It truly is a one-hole-wonder. Quite efficient, if you ask me.
Within the cloaca are three chambers. The coprodeum receives the feces; the urodeum receives the uric acid and is where the reproductive ducts empty; and the proctodeum is the final “holding” chamber where everything is eventually expelled.
So while there is only one exit point for the urinary, digestive, and reproductive tracts in birds, there are still organized compartments within the cloaca for each. This unique anatomy is not without cause, as cloacas serve a specific, evolutionary purpose in birds.
Why Birds Have Cloacas
Birds and reptiles evolved to have cloacas and to expel uric acid for a few important reasons. According to Enviroliteracy, “the cloaca, derived from the Latin word for ‘sewer,’ is a common chamber where waste products from the intestines and kidneys mix with reproductive cells before being expelled from the body. This single opening simplifies anatomy, reducing the number of necessary orifices and associated musculature.” This simplified anatomy results in:
- Water Conservation
Because uric acid is nearly insoluble in water, birds don’t need to drink water to expel it. Plus, the cloaca reabsorbs water from waste material before it is expelled. As such, birds are able to hold onto their water for longer. This means most birds don’t need to drink as much as most mammals do. This is especially advantageous for birds that live in dry climates, fly long distances, or have limited access to fresh water.
- Weight Reduction
Birds need to stay lightweight for flight. Because birds excrete uric acid as a solid substance, they don’t have urinary bladders. This means they aren’t carrying as much body weight. Having a single opening with the cloaca also reduces body weight, as there is less tissue and muscle needed for excretion.
- Simplified Reproduction
Because there is less tissue and muscle involved in the cloaca, it simplifies the reproductive process in birds. This also reduces their weight and allows them to lay eggs rather than grow an embryo in a womb.
No, it’s not just Poop.
When talking about bird poop, we now know we’re not just talking about poop. In some ways, we’re talking about something else entirely, which is why it has its own name: guano. Of course, guano is not all the same, considering that bat and seal poop are also called guano—and they don’t have cloacas or “poop” like birds do.
Nevertheless, calling bird waste “poop” doesn’t quite cover it, as it’s a mixture of uric acid and fecal matter. It’s a one-and-done deal. So the next time you see bird poop, you’ll know it’s not just poop, but mostly the pasty white uric acid.
The Question: Why is Bird “Poop” White? Finally Solved.
As we’ve learned in this blog, poop talk can be quite educational. When we don’t shy away from this stinky business and lean in to get a closer look (but not too close), we learn a great deal about the animals we share our environments with.
Now we know that bird poop isn’t just poop, and that pasty white substance you can’t get off your windshield is a nitrogenous waste product known as uric acid. While we may find it gross, it still tells an interesting story about how unique birds’ urinary and digestive tract systems are.
In taking a closer look at bird poop, we also realize how different we are from our avian friends. From their feathers to their one-hole-wonder cloaca, their anatomy shows remarkable evolutionary intelligence and efficiency.