Most people are all too familiar with the white sludge that can fall from above as you enjoy the outdoors, universally recognized as bird poop. Yet we don’t experience a similar threat, as far as we know, in the form of a liquid bird urine. This begs us to ponder: Do birds pee?
The answer to this question depends on how you define peeing. Basically, no, you don’t need to worry about a pale yellow liquid urine sprinkling you when birds fly above, because birds don’t release that kind of urine. But the complete answer to this question actually takes shape through a series of more specific questions.
Do birds produce urine?
Birds do produce urine, but it has different components than mammalian urine has. Birds, like mammals, have kidneys that filter the blood and manage water and salt balance, sending waste away to be excreted from the body. In humans, nitrogen waste from amino acid metabolism is made into urea, which the kidneys collect for the body to excrete as waste in a watery urine. In birds, the nitrogenous waste from amino acid metabolism is made instead into uric acid. This is excreted in a product that serves the same purpose as urea-based urine, but its different components make it look different as well. Bird urine is a white liquid suspension full of uric acid crystals.
The purpose of having a uric acid-based urine is related to water conservation. Birds live in a variety of environments that are generally dehydrating, and thus birds have adaptations that help them conserve water. Uric acid does not easily dissolve in water, so it can be excreted with far less water than urea can. So, birds do produce a kind of urine that gets rid of body waste, but they lose far less water in this process.
Do birds store urine in a bladder until it’s time to release it?
Birds do not have a bladder in which they store urine. When a bird’s kidneys produce the uric acid-based urine, this urine moves down the ureters and reaches a chamber of space in the bird’s cloaca, which has an opening that can transport materials outside of the body. The cloacal chambers also receive and release feces from the intestines and reproductive substances such as sperm.
Scientists think that for land animals, storing urine in a bladder helps avoid predation. If animals simply released urine continually or often, they would leave a scent trail that would make them susceptible to predators. This potential benefit is less relevant to birds, as flying makes leaving a scent trail for predators less likely and less risky. Also, scientists think the lack of a bladder may be one of several adaptations that help birds remain lightweight, aiding in flight.
How do birds release urine from the body?
Birds do not release urine from the body through an opening at the end of a urethra. Once the urine passes through the ureters to reach the cloacal chambers, the urine and feces mix together and leave the bird’s body through the cloacal opening. Thus, the white sludge that is commonly called bird poop is actually a mix of bird urine and feces and, in fact, often has visible dark solids. In humans, urine leaves through a hole at the end of the urethra, while feces leave through the anus—two separate openings. In birds, the cloaca serves both purposes. It is also the opening for reproductive materials, allowing sperm to leave the body in males and leading to the oviduct and ovary in females.
Are there any exceptions?
The ostrich releases its urine prior to and separately from releasing its feces. Yet the ostrich does not have a bladder separate from the cloaca, where all waste leaves the body. However, scientists think the ostrich stores urine in a cloacal chamber just inside the cloacal opening. This chamber can expand in size to store urine, and its location blocks the path between the cloacal opening and the colon, which is thought to contribute to the separation of urination and defecation. In addition, the ostrich has unique musculature of its cloacal chambers, the end of the colon, and a sphincter muscle between the cloacal chambers and the colon, which is thought to help hold the feces separately.
So, birds do produce pee, but it is very different than mammalian pee. Bird pee is not stored in a bladder but rather in most cases mixes with feces in a cloaca, which releases this waste all together as the white sludge with dark masses you are familiar with and likely just call “bird poop.”