Ducks have to swallow their food whole - from soft plant stems to tough nuts and seeds. But ducks (and all birds) have a secret weapon to help digestion: a gizzard. The gizzard is a sac between the duck's stomach and intestines. The walls of the gizzard have strong muscles with lots of ridges. Food passes into the gizzard from the stomach, where it's already been softened up a bit by mixing with digestive juices. Then, the gizzard's walls squeeze together. This squeezing grinds the food between the ridges, breaking it down. Tiny stones called grit also get stored in the gizzard (ducks eat the grit on purpose). The sharp edges of the stones further break down the food as they grind against it.
A duck floats because its body is light compared to water. Air is lighter than water, and ducks have plenty of places filled with air. All the bones are hollow. Feathers trap air against the duck's body, too. Finally, a duck's body has sacs filled with air like mini balloons to help keep it afloat. How do ducks stay on course during migration? Ducks find their way between the same summer and winter areas year after year. They travel the same routes and use many of the same rest stops each time.
By the time a hen lays an egg, it's fully formed. The egg grows like a layer cake inside the hen's body. The egg begins at the center with the germ, or the part that grows into a duckling. The next layers to form are the yolk and the albumen (al-BYOO-men), also called the white. These layers feed the growing embryo. Finally, the shell forms. A liquid form of calcium (also found in bones) sticks to the albumen and turns into a solid shell. This shell is amazing. It allows oxygen and water to pass through to the duckling inside. At the same time, it's very light and strong.
Ducks navigate, or guide themselves, using a combination of guides. They memorize and follow landmarks like rivers and mountains. They track the position of the sun, moon and stars as they fly. The may also be able to sense how Earthıs magnetic pull changes from place to place, and use this information as a guide.
A layer of fat helps a duck stay warm. So do its feathers. Feathers closest to the skin are soft and fuzzy. They're called down, and they help trap warm air near the duck's body. Outer feathers are coated with oil, which makes them waterproof. This keeps cold water from soaking in.
Well, their arteries and veins run side-by-side. So, warm blood traveling through arteries passes right next to cold blood inside veins which has passed through the legs. This quickly re-heats the cold blood.
Ducks change colors by changing feathers. This is called molting. When ducks molt, all their feathers fall out and are replaced by new ones in just a few weeks. This happens twice a year. The new feathers grow quickly, but for a time the ducks aren't able to fly. So, molting is dangerous for ducks. While all ducks molt, only the males, or drakes, change colors. For nine months of the year, they have brightly colored feathers. The rest of the time, they have dull brown feathers and look a lot like hens.
Where we have hands and arms, ducks have wings to catch the air. These wings are powered by super strong muscles. Ducks are also designed to be as light as possible. Their bones are hollow. They have as few muscles as possible, to keep weight down, too. Feathers also have an important job. They streamline the body, allowing air to pass easily around it. During flight, wing feathers close up and overlap as the wing comes down. This helps the wing push against the air with more force. As the wing moves upward, the feathers spread apart, and the air passes easily between them. This helps keep the duck from being pushed downward.