By Lisa Hadden
As it came time for a decision to be made on the final fourth grade lesson of the year, I was torn. There were still so many options to choose from and things I wanted to teach them.
One of my teachers requested we do chickens because she enjoyed this lesson herself. The more I thought about it, I knew she was right!
Egg-laying chickens are extremely fascinating. They have complex digestive and visual systems, they are intelligent, and they possess a surprise set of adaptations that allow them to produce one of the most versatile foods that humans rely on — the egg.
One of the most interesting facts is that chickens do not have teeth. Therefore, instead of chewing their food, they swallow it whole. The food first stops in their crop. I tell the students that I think of it as their own little suitcase. Their food is stored there for a bit and it softens some. It then passes into the gizzard where it is ground up. Chickens eat small pebbles or grit, and these small pieces act like teeth and help the gizzard to grind the food up.
Chickens are also more intelligent than many people realize. They can recognize over 100 different faces, communicate with a variety of sounds and even establish complex hierarchies — hence the term “pecking order.”
Chickens are considered prey and they have multiple predators. Students always have stories about the different predators that have killed their chickens, ranging from mink to vultures to their own dogs. Because chickens are prey and have so many predators, their eyes are on the side of their head so that they are able to see approximately 300 degrees. The other cool thing they have for protection is three eyelids. The third eyelid, called the nictitating membrane, is the one that protects and moistens the eye. What is amazing is that it is transparent; therefore, they can still see when it is swiping over the eye.
The egg itself, that the hen lays, is a remarkable structure. It actually has nine identifiable parts. The next time you crack an egg open, look inside the broad end of the egg. There you will find the “air cell.” This air cell plays a crucial role in helping a chick take its first breaths just before hatching. Also, take a close look at the yolk. There is a small, white dot that is called the “germinal disc.” That is where the chick would develop if the egg were fertilized. Also, regardless of whether the egg has been fertilized or not, it will still have all of these features.
The process of egg formation inside a hen is complex, but incredibly efficient. On average, it takes about 24-26 hours for a hen to produce a single egg. During this time, the yolk is released from the ovary and travels
through the oviduct. This is where layers of egg white (albumen), membranes and finally, the shell, are added. Hens are born with all of the eggs they will ever produce already inside their ovaries.
If an egg is fertilized and incubated, it takes about 21 days for the egg to hatch. The embryo develops very quickly, relying entirely on the nutrients stored in the yolk. By the final days, the chick uses the air cell to begin breathing internally before pecking its way out of the shell using a specialized structure on its beak called the “egg tooth.”
The eggs that the chicken lays come in a variety of colors. The color depends on the breed of the chicken and has nothing to do with what the chicken eats or the nutritional value of the egg.
Clearly, egg-laying chickens are highly specialized with unique anatomy, behavior and reproductive systems. From their toothless digestion aided by the gizzard to the intricate process of egg formation and the 21-day development of a chick, they are far more complex and interesting than their everyday presence might suggest.
