How Does a Chick Hatch?

Egg Tooth

During embryonic development, a spike forms on the beak of a chick either at the tip or on the upper side of the beak. This spike looks something like a small tooth and is called the egg tooth. In chicken eggs, it must develop prior to the nineteenth day of gestation since they break into the air sac at that time. They must break into the air sac because the pores in the eggshell no longer allow enough oxygen transfer for them to breathe. They will be hatching very soon at 21 days gestation. The egg tooth disappears by the time the chick is two weeks old.

Pipping Muscle

Chicks are equipped during gestation with a special muscle on the back of their necks called a pipping muscle. The strength of the pipping muscle enables the fragile chick to beat against the hard calcium carbonate eggshell for hours until it finally breaks through and eventually emerges. Initially, this large neck muscle contracts to force the chick's egg tooth through the egg's inner membrane to access the air sac so it can breathe a day or two before hatching. This process is called internal pipping. Once the chick has broken through the inner membrane, if you listen carefully, you may hear it chirping. This temporary air supply gives the chick time to break through the eggshell.

External Pipping

A clutch of chicks may begin making clicking noises before actually hatching. This allows them to communicate with other chicks ready to hatch so that they can hatch at the same time. In the wild, this is a protective measure so the chicks can remain together. Once the chick breaks the internal membrane it immediately begins tapping at the eggshell until it breaks a small hole and begins to breathe outside air. This process is called external pipping. As the chick continues to hammer at the opening, you will begin to see the tip of the beak through the hole. The chick also turns and pushes in the shell; creating a crack that helps it open the shell and escape. The chick emerges wet and tired and may rest for a few hours until it dries.

Resources

• Chick Embryo Development
• As Scarce as Hens' Teeth
• Raise Champion Turkeys for 4-H or Pleasure