What about the act of feeding? Surely the duck feels discomfort when a tube is slid down its throat?
Tony Bourdain likes to remind us that we see worse things committed against human beings on late night pay-per-view. And he's right: humans have a gag reflex. But ducks? Not so. I tried hard to find a good video online of a duck eating fish, but they are all too blurry or too annoying to watch. The closest I came is this video of a cormorant, another migratory waterfowl.
Watch closely as it swallows a spiky fish several times wider than its neck.
Incredible, right? And that, folks, is the reason why ducks don't struggle when a feeding tube deposits food in its throat. Its body is built for exactly the same type of stress in the wild.
Humans chew their food in their mouth until it breaks down into pieces small enough to swallow. Ducks, on the other hand, have no teeth in their mouth, and they don't chew. Instead, they swallow their food whole, storing it in the bottom of the eso****us in a stretchy pouch known as the crop. Eventually, the solid food works its way into a stomach and a sac-like organ called the gizzard. Throughout the day, a duck will swallow small rocks and pebbles, which get stored in the gizzard. Once food enters it, the muscular organ uses the pebbles as make-shift teeth, grinding up the food so the duck can digest it.
Because of this, their eso****i are custom-built for stretching. I had Bob send a few of them to the office where I tied off one end and filled it up, water-balloon style in order to see exactly how much a duck can hold in its crop. The four we tested stretched out to a little over a quart of liquid apiece, or around 950 grams