Inside the Avain (chicken) Egg
by Sherri Carpenter
Spring 2003
Cell division begins as soon as fertilization takes place. When the egg is laid, cell division stops until proper environmental conditions are established for incubation. When incubation begins, cellular growth continues. In the beginning most cell are indistinguishable, but as the embryo develops, cell distinction becomes observable and the cells start to form the vital organs and body of the soon to be baby bird.
DAY 1
Before the first day of incubation has ended, the head and precursor of the digestive tract has become distinguishable. Blood islands appear that will later developed into the blood system and neural folds that will later become the neural groove. The eye is also starting to develop.
DAY 2
The second day, parts of the brain are developing, the ears are beginning and the lens of the eyes is forming. The embryo is developed enough that it is starting to arch and flex inside of the egg.
DAY 3
At the end of the third day limbs are just being formed. Three visceral (internal organs enclosed within a cavity) cleft (gills) have formed on each side of the head and neck and will play an important part in developing into the eustachian tubes (in the ear), face, jaw and some ductless glands. The amnion fluid has surrounded the embryo to protect it and maintain proper development. The tail is beginning to show. The allantois has developed which is a respiratory and excretory organ for the embryo. Nourishment from the shell, (albumen and calcium) are transported to the embryo through the allantois.
DAY 4
By the end of the fourth day the chick has all the organs necessary to sustain life and most of the organs can be identified. The chick’s body turns 90 degrees and lies down with its left side on the yolk and the head and tail come close together so the body creates a C-shape. The respiratory and digestive systems develop, along with the mouth, tongue and nasal pits. The heart continues to grow and beat even though it is not fully enclosed in the body yet. At this stage the chick embryo looks just like that of a mammal embryo.
DAY 7
As the embryo continues to grow the circulatory system covers about ½ the yolk. By the seventh day the heart is fully enclosed in the chest, wings and feet are being seen and the head is about the size of the rest of the body. The beak is forming the egg tooth.
DAY 8-10
In the next few days the head and beak will be well formed, toes can be seen, the beginning of feather formation is starting, eyelids begin to cover the eyes and the body begins to grow faster.
DAY 11
By the eleventh day, weight has doubled in two days. Weight will again double in two days. Blood vessel can be seen inside the embryo; the ear opening is evident and skin has taken on a texture indicating where feathers will grow. Bones in the eyes, skull and toe joint are visible.
DAY 12-19
As the embryo continues to grow, each day brings new development. The twelfth day feathers are seen in the tail area and feather tracts are visible. Scales and nails on the feet form and the eyelid almost covers the eye and the beak has hardened. By the fourteenth day feathers cover most of the body, the eyelid has completely covered the eye and the head turns towards the large end of the egg positioning itself for later hatching. The head, body and limbs are balancing out in size. By the sixteenth day the supply of albumen is exhausted, so its sole source of nutrients comes from the yolk. The yolk decreases in size; the beak, claws and scales are hardening and the head turns so the beak is under the right wing.
DAY 20
By day twenty, the eyelids are closed, toes are distinct and feathers are well developed. The head is positioned towards the large end of the egg, beak under the right wing and feet drawn up toward the head. The chick is getting ready to hatch. The yolk sac withdraws into the abdomen. The navel will close and heal once the yolk sac fully retracts. The allantois, which has served as its lungs, will no longer carry enough oxygen for the chick.
HATCHING
Inside the egg, the carbon dioxide has built up due to the allantois not being able to meet the gaseous exchanging needs. This build up causes the neck muscles to twitch. This twitching motion, (providing the chick is positioned correctly) along with its egg tooth, will pierce the air cell and the allantois begins to dry up as the chick uses its lungs. During the incubation period water in the egg has evaporated which helps increases the size of the air cell.
As the chick breathes the air in the air cell, the carbon dioxide levels rise to 10% and induce more neck twitching which causes the egg tooth to penetrate the shell. The chick rests, changes position and keeps cutting until its head fall free from the egg. The chick uses its right wing as a guide for pipping the circular path forming the cap through which the chick will break through. During this process of pipping the egg gives off ammonia and carbon dioxide. Soon after hatching the egg tooth falls off.
Species |
Incubation period |
Pip to hatch interval |
Amazon: Yellow naped, Yellow front, Yellow crowned, Double-yellow headed, Blue front, White front |
28-29 days |
24-48 hours |
Conure: Aratinga, |
24 days |
24-48 hours |
African: African Grey |
28 days |
24-72 hours |
Cockatoos: Umbrella, Moluccan |
28 days |
24-48 hours |
Macaws: Blue and Gold, Green winged, |
26 days |
24-48 hours |
Eclectus |
28 days |
24-72 hours |
Caique |
25 days |
24-48 hour |
Quaker Parakeet |
23 days |
24-48 hours |
Cockatiel |
21 days |
24-48 hours |
Budgerigar |
18 days |
24-72 hours |
Lovebird |
22 days |
24-48 hours |
Lories |
27 days |
24-48 hours |
Pionus |
25-26 days |
24-48 hour |
Grey Cheeked |
22 days |
24-36 hour |
Parrotlets |
19 days |
24-36 hours |
Parrots are altricial, which means they are hatched helpless, eyes closed and often nake; wheras birds that hatch with eyes open, covered with down and moving around are called precocial. Although the time frame of development between chicken and parrot embryos will differ slightly the growth development will follow along the same pattern.