Occasionally I rerun a favorite older post. This one was originally published in May of 2015. For this version I’ve edited the text, changed the title slightly, tweaked the formatting and added a photo.
For reasons that will become obvious, this post brings back strong memories of my teaching days and the many opportunities this particular subject gave me to use a sophomoric sense of humor with my high school students as a teaching tool. With this presentation I’ll resist most of those opportunities but knowing me, I’ll probably slip one in.
Since you’re reading this you’re probably a birder, bird photographer or nature lover so you’ve seen your share of pooping birds. But bird poop isn’t really “poop” in the traditional sense – its composition is quite different from mammal poop, including that of humans, and that incredibly fortunate adaptation originated with the shelled egg.
Most mammals excrete their toxic nitrogenous wastes in the form of urea but birds and reptiles produce uric acid instead. There’s good reason for that. Urea is soluble in water and in mammals is excreted in dissolved form in their familiar urine, which is mostly water. But birds as developing embryos must survive their time in the egg with their toxic wastes also enclosed within the shell which is a problem not faced by live-bearing mammals. If birds produced water-soluble urea, the urea would quickly build to toxic levels throughout the egg and kill the embryo. So birds produce uric acid instead. Uric acid is insoluble in water and crystallizes out of solution and is stored harmlessly within the egg, and separately from the embryo, until hatching.
After hatching, birds concentrate and store uric acid within the cloaca before it is voided. Birds can excrete 1 gram of undissolved uric acid in less than 3 ml of water but mammals require up to 60 ml of water to excrete the same amount of urea so this is also a weight-saving device for flight. Water (urine) is heavy. Imagine birds trying to take off or maneuver in flight with their “tank” (urinary bladder, a structure lacking in birds) full of heavy, sloshing urine…
In birds, sexual products (sperm and eggs), metabolic wastes (uric acid) and digestive wastes (feces) must all pass through the cloaca (which literally means “common sewer”). The cloaca is a storage chamber opening to the outside at the vent. So birds have only one opening to the outside for elimination of these products, while mammals typically have two.
Sorry for all the heavy reading but this explains some things we’ve all seen in the field. Birds excrete uric acid in the form of a relatively thick white paste (darker digestive wastes that haven’t been eliminated through the mouth as pellets may also be included) instead of water- based urine, as in mammals.
That paste collects on habitual perches and many of us call it “whitewash”. It can be aggravating to photographers because some see it as unsightly in their photos. It’s more than aggravating to car owners. Because of its insolubility in water, whitewash is incredibly persistent. I don’t think Noah’s floods would wash it away.
This rocky perch, part of a huge boulder on the slopes of Antelope Island’s Frary Peak, is a favorite perch for birds like Red-tailed Hawks, Chukars, Western Meadowlarks, Rock Wrens, Sage Thrashers and Lark Sparrows but I seldom use any photos of birds using this perch because the rock is so heavily stained with incredibly bright and persistent whitewash. Several years ago I noticed that even after a huge rainstorm the whitewash had been unaffected so using some bottled water I attempted to scrub away a tiny portion of the whitewash as a test. It simply would not come off.
Water is often referred to as the “universal solvent” but obviously even water has its limits.
Several of the following s are soft but I think they’re sharp enough to make my points.
Some birds take in so much water in their diet that excess amounts of it must also be voided – many hummingbirds are a case in point. Flower nectar is mostly water so hummers have to ingest a lot of water to meet their nutritional requirements.
I photographed this one as it was feeding on Rocky Mountain Bee Plant on Antelope Island and just happened to push the shutter button as it voided some of that excess water. The water also contained some white uric acid (out of solution of course) but as you can see it’s mostly water.
Prior to nesting season the diet of Williamson’s Sapsuckers is made up almost entirely of tree sap harvested at sap wells like you see here.
Here you can see the male of the mated pair taking a sap break in-between bouts of defending (or attempting to establish) his nesting territory from the likes of Northern Flickers, Mountain Bluebirds and Red-breasted Nuthatches.
So, you guessed it, the sapsucker soon voided a big batch of excess water. After the eggs are laid these birds begin to consume lots of ants and at that point their wastes would also include darker indigestible chitin from their exoskeletons.
There’s another consequence of birds having a cloaca and eliminating sexual products, sperm and eggs, through the cloacal opening.
Since most birds lack a penis (ducks, geese, swans and large ratites are exceptions), sperm must be passed from male to female through the awkward process of pressing their cloacal openings together. Some folks call this act the “cloacal kiss”.
OK, I’ve babbled on for too long. I hope you’ll forgive, or at least tolerate, the bio-geekiness of this post. It may not be for everyone but this stuff fascinates me so…
“Thus from an embryonic necessity was born an adult virtue”. Before it is expelled, adult birds concentrate and store uric acid inside the cloaca. This is also a weight-saving device for flight because mammals need up to 60 ml of water to excrete the same amount of urea, whereas birds can excrete 1 gram of undissolved uric acid in less than 3 ml. Imagine attempting to take off or maneuver in flight with your “tank” (urinary bladder, a structure absent in birds) full of sloshing urine—water (urine) is heavy.
You must be a nature lover, birdwatcher, or photographer if you’re reading this, and you’ve undoubtedly seen your fair share of “pooping” birds. Well. , most of it isn’t actually feces in the conventional sense; rather, its composition differs slightly from what most people believe, and that adaptation came from the shelled egg. First, some background (I swear not to call it “poop” again):
In between defending (or trying to establish) its nesting territory from birds such as Northern Flickers, Mountain Bluebirds, and Red-breasted Nuthatches, the male of the mated pair is seen here taking a sap break. Tree sap is also mostly water so….
The cloaca, a storage chamber that opens to the outside at the vent, is where sexual products (eggs and sperm), metabolic wastes (uric acid), and digestive wastes (feces) must all pass. The cloaca literally means “common sewer.” Therefore, whereas mammals normally have two openings to the outside for the removal of these products, birds only have one.
Sorry for the lengthy read, but this clarifies a few things that all of us have witnessed in the field. Rather than excreting water-based urine like mammals do, birds instead excrete uric acid as a relatively thick white paste, sometimes with darker digestive wastes mixed in.
You guessed it: the sapsucker quickly voided a sizable amount of extra water. Following the laying of their eggs, these birds start eating a lot of ants, which causes their waste to contain darker, indigestible chitin from their exoskeletons.
Birds and reptiles create uric acid instead of the toxic nitrogenous wastes that most mammals excrete in the form of urea. There’s good reason for that. Since urea dissolves in water, it is expelled by mammals in the dissolved form in their well-known urine, which is primarily composed of water. However, birds do not have to deal with the challenge of surviving their time in the egg with their toxic wastes also contained within the shell, as they are developing embryos. In the event that birds produced water-soluble urea, the urea would swiftly accumulate to lethal concentrations inside the egg, killing the embryo. So birds produce uric acid instead. Uric acid is kept safely inside the egg and apart from the embryo until hatching. It is insoluble in water and crystallizes out of solution.
You’re probably a birder, photographer, or lover of the outdoors if you’re reading this, so you’ve probably seen your fair share of pooping birds. However, bird poop isn’t actually “poop” in the conventional sense because it differs greatly in composition from that of mammals, including humans, and because of an extraordinarily fortunate adaptation that began with the shelled egg.
In birds, the cloaca, which literally translates to “common sewer,” is required to be passed through by sexual products (eggs and sperm), metabolic wastes (uric acid), and digestive wastes (feces). The cloaca is a storage chamber that has a vent opening to the outside. Therefore, whereas mammals normally have two openings to the outside for the removal of these products, birds only have one.
This post reminds me a lot of my teaching days and all the opportunities this subject gave me to use a sophomoric sense of humor as a teaching tool with my high school students, for reasons that will become clear. I’ll decline the majority of those opportunities with this presentation, but knowing me, I’ll probably sneak one in.
FAQ
Where do birds poop out of?
Do baby birds poop right after they eat?
What is the white stuff baby birds spit up?
Do birds poop out eggs?