For farmyard and wild ducks alike, nesting typically occurs in early to mid-spring. Duck hens lay about a dozen or so eggs, which take nearly a month to hatch. A mother duck sitting on her eggs is "brooding", and her collection of eggs -- and eventually ducklings -- is known as a brood. Brooding provides heat during the important incubation period; the time it takes for the eggs to hatch.
All in a Month's Work
After a successful mating, the mother duck prepares to nest by plucking down feathers from her abdomen, creating a bald area known as a "brood patch." She arranges the plucked feathers around the bottom and sides of the nest to provide additional warmth and insulation. The plucking also results in an additional benefit: blood vessels run close to the duck's skin in the brood patch, and pass heat from the mother directly to the eggs.
Duck mothers lay a single egg per day, and in the end her "clutch" size, the amount of eggs she has laid, will be around 8 to 14 eggs. When her laying is complete, the brooding duck will begin to incubate her eggs around the clock. During this time, she will need to take breaks for food and water, however these moments are brief. A mother duck sits on her eggs for 20 to 23 hours a day, taking an average of three breaks, each lasting around an hour at a time. When she does leave her nest, the duck hen covers her eggs with additional down and nesting material to help keep the eggs warm in her absence.
The incubation period lasts an average of 28 days, about a month. With the mother duck spending so little time away from the nest, she relies on stored fat to survive. A couple of days before the eggs are ready to hatch, small cracks begin to appear, and the ducklings will begin peeping from inside their eggs. Then, in a span of 24 hours, all the ducklings will hatch from their eggs, using a small sharp bump on their bills called an "egg tooth." The egg tooth falls off quickly after hatching.
Once all the ducklings have hatched, the mother duck typically spends one more night on the nest, helping to warm and dry the newly hatched brood. The next day, she will begin to take the ducklings out to find food and forage, as they follow her closely.
A Little Help with Babysitting
Many domestic ducks have no experience with brooding or incubating, and tend to neglect their nests or ducklings. When this occurs, fertile eggs are usually incubated by a broody hen, if one is available, or by artificial incubation. The amount of time required to hatch the eggs is the same, however hens cannot typically keep an entire clutch of duck eggs warm, due to the large size of the eggs in comparison to her body.