Cockatiel Egg Hatching

When a cockatiel egg is ready to hatch the chick undergoes different chemical changes within the body due to different conditions that occur inside the egg. Below is a description of the hatching process and a series of pictures I was lucky enough to get of one of my eggs hatching.

Egg Hatching Process

Egg hatching normally begins approximately 16 - 21 days after the initial incubation by the parents commences. During this incubation period the chick has grown to look like the chick we recognise and through that growth has continually used resources within the egg and also released waste products. The egg has lost weight compared to the weight when it was laid due to loss of water through the membrane and also due to the chick metabolising fats from the yolk. The chick also absorbs calcium from the inner lining of the shell making it thinner and lighter in weight. Just before it hatches the chick will also draw up the remaining yolk sac into its abdomen and orally take in any fluid that remains inside the shell. All these factors can mean a reduction of around 10% in the weight of the egg over the total incubation period.

Just prior to hatching the air sac in the larger rounded end of the egg will appear enlarged and occupy 20 - 30% of the volume of the egg. The tooth like prong on the end of the beak that the chick has developed to assist in hatching pierces the air sac and causes this enlargement and the chick takes its first breath of air. This process of the air sac becoming bigger is called the "draw down" process and can be seen when candling. Because the inside of the egg is still not open to the outside air the chick causes an increase in the carbon dioxide level within the air sac as it breathes. The rise in CO2 causes muscles to contract in the abdomen and thus the yolk sac gets drawn into the body. This rise in carbon dioxide also causes twitching or contracting of the muscle at the back of the neck that is enlarged at this stage to help with the pipping process. This contracting causes the tooth like prong or egg-tooth to pierce the inner shell membrane and create what we see as the first pip in the shell.

The contracting neck muscles makes the head move in a jerking motion. Along with causing the egg-tooth to break through the shell it also causes the chick to rotate with in the shell. This creates a line of pip marks around the end of the shell and gives almost like a separate top to the egg that the chick can then push off. The moisture retained within the shell membrane is used as a lubricant to allow the chick to rotate and eventually break free of the shell.

This complete process from the initial draw down of the air sac to hatching normally takes from 24 - 48 hours. Anything longer than this usually means there is a problem and an assist hatch may be necessary. If everything appears normal then it is best not to intervene until it becomes absolutely necessary. I will cover the subject of assist hatches and hatching problems in another article.

Egg Hatching Pictures

Here is a series of pictures I took a while ago of a chick in the process of hatching. From the first picture to the last took approximately 15 minutes. During the final stages the gap in the shell would open and then close as the baby pushed and then rested.

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