Whether you’re a nature enthusiast or backyard duck parent, learning how a duck’s digestive system works is fascinating. In this article, you’ll get to follow a snail as it travels from bill to tail through Primrose the duck!
Do ducks have teeth?
Let’s get this question out of the way first, because it’s so commonly asked… No, ducks don’t have true teeth like you do.
Instead of teeth, ducks have specialized serrated mouth parts called lamellae on the insides of their bills. If you rub your finger across a duck’s lamellae, they feel similar to the end of a slightly sharp comb.
Lamellae provide ducks with the ability to grip something more firmly and/or rip, which is ideal if you’re hunting frogs and crayfish or pulling pond plants. Having been nibbled on countless times by our Welsh Harlequin ducks, we can say that duck bites are more entertaining than injurious to humans.
What are duck bills and lamellae made of?
Most domesticated ducks have been bred to be flightless, however they’re still anatomically indistinguishable from their wild Mallard ancestors. That means every body part on a duck is adapted to facilitate flight, e.g. gram per gram they’re marvelously strong yet lightweight.
A duck’s bill is a perfect example of this trait. The core of a duck bill is composed of lightweight boney projections emerging from the skull that are covered by a sheath of keratin. For reference, keratin is the same protein fiber your fingernails and hair are made of and also the same stuff that makes everything from armadillo shells to horse hooves to cow horns.
Duck lamellae (their teeth-like structures) are also made of keratin. One of the interesting features of the keratin portion of a duck’s bill is that it’s always growing, being ground down, and/or shedding.
If one of your teeth breaks off, it won’t grow back. If a duck lamella breaks, it grows back. (Another reason that ducks are superior lifeforms.)
The nail (the hard pointy tip of a duck’s bill) is also made of keratin.
What do wild Mallards eat?
Wild ducks’ lamellae and digestive systems are optimized to help them survive in food-rich aquatic environments full of larger predators. Ducks don’t sit down to four-course meals, they have to grab, swallow, and move on quickly before something grabs and swallows them. The “chewing” takes place later on in their digestive systems (more on that below).
Each species of duck occupies a specific ecological niche, to which its body shape and function are specifically adapted. Wild Mallards are “dabbling ducks” whose diets consist of aquatic plants, nuts, seeds, and small animals. The macronutrient composition of a Mallard duck’s diet will vary with the seasons, from more carbohydrate-rich in the cooler months to more protein-rich in the warmer months.
If you have Mallard-derived domesticated ducks like we do, you’ll notice your ducks’ physical features much more closely resemble their Mallard ancestors than other wild duck species.
For example, a common merganser is a diving duck built to swim underwater and catch fish. Hence its longer, thinner, and sharper bill shape relative to a Mallard or our domesticated Welsh Harlequins.
How does a duck’s digestive system work?
To detail how a duck’s digestive system works, we’d like to introduce you to Primrose, one of our Mallard-derived Welsh Harlequin ducks. Let’s follow a snail (one of Primrose’s favorite foraged garden treats) from bill to tail through her digestive system…
1. Nail, tongue, and throat
First, Primrose grabs the unsuspecting snail with the nail of her bill, then quickly tosses it back to her tongue. The hair-like structures on her tongue help move the snail back towards her throat while specialized taste buds determine whether the food item is tasty and good enough to go down the hatch. (Or whether it’s too large which could cause her to choke.)
Here we should also mention that ducks are not good candidates to be sommeliers. They only have about 400 taste buds compared to about 9,000 in humans.
Primrose’s tongue directs the whole un-chewed snail down her throat, carefully avoiding the glottis. The glottis is the windpipe/hole in the middle of her throat at the back of her tongue, which opens and closes allowing her to breathe. A snail going down the glottis would likely mean death.
Primrose the duck’s mouth also contains some saliva which helps facilitate the swallowing of the snail and gives it a dash of digestive enzymes.
The first stop for the snail after going down Primrose’s throat: the esophagus. A duck’s esophagus is akin to a grocery cart. It stores all the food she wants to save for later when she’s out of harm’s way. (Granted, Primrose isn’t actually in harm’s way in our yard, but her genes and Mallardesque duck brain haven’t gotten the memo.)
A common misconception is that ducks have crops, which is a specialized widened area of the esophagus. While many types of birds do have true crops, ducks do not. Their esophagus simply expands to meet the size demands of the meal.
A humorous side note if you have ducks: you may notice their chests look a bit swollen or even lopsided after a large meal. This is due to them stuffing their “grocery cart” (esophagus) full of food. As the esophagus empties, physiological warning bells go off prompting a duck to eat again. “Get more snails and kale, Primrose!”
3. Glandular stomach/proventriculus
Now the snail enters Primrose’s glandular stomach, aka proventriculus, where it gets bathed in a soup of digestive enzymes. This process is akin to the spray of soap and water at an automated car wash before the real action starts.
If you were to magically remove the snail from Primrose’s esophagus at this point, its shell would still likely be intact but the exposed skin wouldn’t be so pretty.
The next stop on our merry snail’s journey through a duck’s digestive system is Primrose’s ventriculus or gizzard. Here’s where a duck’s digestive system gets down to the business of “chewing,” albeit without teeth or jaws.
The strong, dense muscles of a duck’s gizzard exert enormous pressure on the contents inside, but they also have help… Just like the dinosaurs we all learned about in elementary school, ducks swallow rocks and grit to aid in digestion.
The crushing force of the ventricular muscles and the grinding of the rocks and grit inside make quick work of the snail shell and partially melted snail. Primrose’s beautiful little duck body also begins to uptake some nutrients (primarily proteins) from the snail at this point in digestion.
6. Small intestine
Like mammals, the small intestines of birds (including Primrose the Duck) are comprised of segments called the duodenum, jejunum and ileum.
In the small intestine, bile from the liver and additional digestive enzymes from the pancreas help extract more nutrients from what’s left of the snail. These nutrients are then absorbed into the bloodstream via epithelial cells lining the intestinal wall.
Our friendly neighborhood snail — which now looks like it’s been put through a blender — next moves to the ceca (plural form of cecum), which look like two squiggly tubes. The ceca’s function is to slurp up any remaining bioavailable nutrients and absorb water. Mmm, sparkling fresh snail water!
If a duck dined on plants, the cecum breaks down the cellulose and absorbs the micronutrients. In the case of our snail: protein, calcium (from the shell) and other micronutrients are absorbed. Rather than simply being a mechanical process, this step in digestion also relies on fermentation aided by certain microbial partners. The emptying of the full fermented contents of the ceca is what accounts for the horrid smelling, oily poo that ducks (including Primrose) pass a few times each day.
After passing through the ceca, our digested and fermented snail looks pretty much like a pile of goo, er poo. (*The cecum is also arguably the first part of the large intestine.)
7. Large intestine & cloaca
The snail is almost done with its journey through Primrose the duck’s digestive system! The large intestine — the largest section of which is the colon — primarily serves to absorb any remaining water and electrolytes.
Finally, the digested snail enters back into the world through Primrose’s cloaca/vent. A duck’s cloaca serves her reproductive, urinary, and digestive systems all at once.
Ducks and other birds don’t have a urethra like you do, so they don’t pee. Everything is expelled through the cloaca, including excess nitrogen that’s been converted to uric acid by their kidneys.
Soon, Primrose’s poo-snail will be eaten by a trillion other microbes and utilized as fertilizer by plants in our garden. Other snails will likely dine on some of those plants and Primrose will dine on those snails, and around and around we go. The cycle of life.
Now you have a good idea of what’s going on when your ducks eat their feed & treats; raid your garden; or devour worms, mollusks and other goodies while foraging in your yard. Duck digestion might appear to be a simple process, but it’s incredibly complex.
Maybe you’ll appreciate all the hard work your ducks went through next time they poop, which will likely happen within a few minutes. That’s because ducks can poop nearly 100 times in a single day. Run snails, run!
Flap on over to these other duck articles:
- Amazing duck eyesight facts
- Duck eggs vs chicken eggs: how do they compare?
- Understanding duck mating and courtship
- 9 amazing duck facts that will blow your human mind
- A fowl battle: ducks vs chickens
- … and more helpful duck articles from Tyrant Farms
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Alexandra StickelsApril 28, 2022 at 6:27 pm
Thank you for writing this very informative article.
Quick question that you might know the answer to:
How long does it take for whatever is eaten to fully go through a duck’s digestive system? Thank you.
Aaron von FrankApril 29, 2022 at 10:50 am
Thanks, Alexandra! It only take a few hours for food to pass through a duck’s digestive system. There is probably some variability based on food type and density, example: acorns vs minnows vs fruit. One way we know how fast a duck’s digestive system works is because our ducks love tomatoes. When we feed them red tomatoes, the color shows up in their feces within 2-3 hours max.
bill evisonFebruary 17, 2022 at 4:33 pm
however i am led to believe ducks (like geese) do not have the commensal bacteria to ‘digest’ ie breakdown the cellulose cell walls of any vegetation eaten
They can only release the contents of plant cells through the grinding process of grit/stones in gizzard!?
Would appreciate a response
Aaron von FrankFebruary 17, 2022 at 11:10 pm
Interesting question! I don’t have a definitive answer, but I’ll share some thoughts:
1. Most geese species (and I believe all domesticated geese) are herbivores. Most duck species are omnivores, and I’m confident saying that all domesticated ducks, whether Mallard-derived or Muscovies, are omnivores. Given that: a) they’re different genera, and b) they have different diets, my guess is they likely have different species (and ratios) of bacteria, fungi, etc in their microbiomes.
2. As you mentioned, geese aren’t very efficient at digesting plant material, despite being herbivores. This is why they spend an inordinate amount of time eating and pooping. (Food can pass through their digestive systems in as little as 30 minutes.) One study found, “The digestion of total organic matter averaged 37% in both species of geese, indicating that geese are less efficient at digesting plant material than most other vertebrate herbivores. The low total organic matter digestion was largely a result of inefficient digestion of cell wall polysaccharides. Geese digested 28% of the cellulose and 25% of the hemicelluloses present in their plant food. In contrast, the apparent digestibility of soluble carbohydrates were 69—85%, and the digestibility of protein (61—80%) was similar to that of most other vertebrate herbivores or graminoid diets.” (source: https://www.jstor.org/stable/1938581)
3. My guess is that geese’ and ducks’ digestive systems are roughly equivalent in their inefficiency at digesting cellulose. Exact numbers are known on geese (#2 above); I don’t have exact data on ducks’s cellulose digestive efficiency. Also unknown: what portion of cellulose that IS digested is attributable to grinding processes in the gizzard vs resident microbes throughout their digestive system? My guess: both play a significant role, with some variability by genera and species.
Hope this helps!
SheilaghJune 18, 2021 at 6:11 pm
Loved this article. Didn’t quite know there was oily poop, although I have made a mental note a few times (and obviously forgot, otherwise I’d have only done it once…) to find out why sometimes instead of the normal poop, a liquid-ish white substance comes out and swirls around in the water.
Aaron von FrankJune 19, 2021 at 12:27 pm
The white part of duck poop (and other birds) is uric acid, which is basically the pee portion of their excreta. The darker bits are the poo portions. As the article details, their digestive systems work different than mammalian digestive systems so everything comes out at the same time, rather than via two separate systems. There will be variance in excreta composition based on how much they recently ate or drank (or what they recently ate and drank). For instance, if we give our ducks a bowl of greens in the morning, we’ll almost certainly see some greenish colored excreta soon thereafter with very little (or no) white in it. If they don’t eat solid food for a bit but drink a bunch of water, you might expect to see more white colored excreta.
Sue UrquhartMay 26, 2021 at 9:43 am
Fascinating! Thank you for this article!
Aaron von FrankMay 26, 2021 at 10:31 am
Thanks, Sue! Glad you enjoyed learning about “duck teeth.” Ha! 🙂