The typical incubation period for a duck egg is approximately 28 days, though this can vary slightly depending on the breed. The final few days before hatching are filled with anticipation about the developing duckling inside. Observing the egg during this stage offers unique insights into the transformation from a single cell to a fully formed, independent bird. The egg’s appearance changes dramatically from the inside out as the duckling prepares for its final breakout.
The External Features of a Developing Egg
The outward appearance of a duck egg remains largely constant throughout the 28-day incubation timeline. Shell colors vary by breed, ranging from bright white to pale green or light blue. Freshly laid eggs are covered with a protective waxy coating called the bloom, which helps seal the shell’s pores to reduce bacterial entry and moisture loss. This coating may dull during incubation, but the shell’s physical structure does not change. No visible changes on the shell’s surface indicate the duckling’s progress until it begins to break through.
Visualizing Internal Development Through Candling
The most informative way to check the duckling’s progress in the final days is through candling, which involves shining a bright light through the eggshell. By Day 25 or Day 26, the egg presents a specific internal appearance. The vast majority of the egg is occupied by a dark, opaque mass—the fully developed embryo. The embryo has absorbed the yolk and grown to fill nearly all the available internal space, and the extensive network of blood vessels has been mostly absorbed.
The only area that remains translucent is the air cell, located at the blunt end of the egg. This air cell expands significantly throughout incubation as moisture evaporates, sometimes occupying up to one-third of the egg’s volume. Just before hatching, the duckling pushes its beak into the air cell, known as internal pipping, allowing it to take its first breath of air. This internal pip may be visually detected during candling as a jagged or irregular line along the air cell boundary.
Audible and Physical Signs of Hatching
Once the duckling has successfully internally pipped, a change in the egg’s physical behavior and sound will often follow within 24 to 48 hours. The duckling’s movements to break the shell can cause the egg to rock or wobble noticeably inside the incubator or nest. This movement is an unmistakable sign that the final, energy-intensive stage of hatching is underway. The increased gas exchange following the internal pip also enables the duckling to begin vocalizing.
Audible peeping, chirping, or clicking sounds can be heard coming from inside the egg, indicating the duckling is alive and active. The duckling uses a small, hardened structure on its bill called the egg tooth to make the first hole in the outer shell, known as the external pip. The final action is “zipping,” where the duckling uses its egg tooth and neck muscles to cut a line around the circumference of the shell, allowing it to push the cap off and finally emerge.