Students explore how an embryo develops inside of a chicken egg over time, discuss life cycles and other natural cycles, and observe similarities and differences between parents and offspring. Grades K-2

candling: shining a light into an egg in order to examine the inside of it

embryology: the study of embryos (unborn human or animal in the earliest stages of growth when its basic structures are being formed) and their development

setting: starting the process of hatching chicks by providing consistent heat and humidity; in the case of humans this means placing them in an incubator; in the case of chickens this means sitting on the eggs

zygote: the first cell formed for an organism that has two parents

Eggs are a bit mysterious. The same egg a chicken lays to create the next generation of chickens is what you find in the grocery store refrigerator and take home to scramble. Students may worry that they are eating baby chicks; put these fears to rest! Eggs in the store are not fertile. The simple explanation of “not fertile” is that there are no developing chicks inside the eggs. A more complex explanation is that a rooster (male) needs to be present to fertilize the hen (female) to produce a fertile egg that will result in a chick. If there isn’t a rooster around, as is the case in grocery store egg production, the egg that the hen lays will not have the complete genetic information that is required for the first cell in the egg to begin to grow and divide.

Fertile eggs contain a living organism—an embryo that will be called a chick when it is fully developed. Embryology is a branch of biology that studies embryos (fertilized eggs) of biological organisms and their development. In a fertile chicken egg, a heartbeat can be seen by candling approximately three days after setting (the point at which the egg begins to be kept warm by a hen or incubator). Candling involves shining a bright light through the egg, allowing one to see the silhouette of the embryo that will become the chick—complete with beak and toes. While candling is truly exciting for adults and children alike, the experience leaves behind almost as many questions about what is going on inside the egg as it provides answers.

The chick embryo develops for 21 days. In that amount of time, the new chicken inside the egg will go from being a single-celled zygote (the first cell formed after fertilization) to a fully developed and functional chick that can peck its way out of the egg shell all on its own and walk, eat, and drink within minutes of hatching.

The old riddle, “Which came first, the chicken or the egg?” is a good starting point for talking about cycles. The question tries to get a person to decide where the beginning point is in a life cycle, but eggs come from chickens and chickens come from eggs, so it’s really the wrong question altogether! Instead of looking at the situation as having a beginning and an end, it is important to recognize that cyclical patterns exist in nature. This concept can be difficult for students who are more accustomed to considering short-term cause and effect situations. Presenting different life cycle examples as well as other examples of natural cycles (the water cycle, the cycle of seasons, etc.) can be helpful in getting students to think cyclically (something that returns to the beginning point) instead of linearly (something that has a definitive beginning/ending point).

1. Ask students where they think the eggs in the grocery store come from. (chickens) Then, ask how many eggs they think are sold in one month in the United States (billions; find recent statistics from the American Egg Board). It takes a lot of chickens to lay that many eggs. Where do all those chickens come from? 
2. Show students the video How It’s Made - Hatchery Chicks.
3. Tell students that in the following activities they will explore the development of a chick embryo inside an egg, the life cycle of chickens, and the similarities between chicks and their parents.

Activity 1: Countdown to Hatch

1. Share the Hatching Science: 21 Days of Discovery PowerPoint or video with your class.
2. Prior to class, use a permanent marker to number the outside of the plastic eggs 1-21. Copy the Countdown to Hatch Inserts so that the egg illustrations are on one side of each page and the milestone descriptions are on the other side. Cut apart the egg illustrations and place each one in the corresponding numbered eggs. Once the eggs are assembled, each egg will contain a picture of the developing chick with a summary of the milestones the chick has achieved on or around that day.
3. Open one egg each day for the course of 21 days. You can choose to open the weekend eggs the Friday before or the Monday after each weekend. 
   • Note: This activity makes a great complement to a classroom hatching project. If you are going to hatch live chicks in your classroom, be sure to time the Countdown to Hatch project to your hatching date so that students can envision what is going on inside the real eggs even though the eggs don’t seem to change on the outside.
4. On day 21 when you open the final egg, have a “hatch-day” party for the new chick (the term “birthday” is reserved for mammals). Discuss the process that you have observed over the last few weeks and what the chick’s needs will be now that it has hatched. Chicks need heat until they get big enough to make their own as well as food and water to stay alive. On farms, people provide these things, but mother hens can also keep the chicks warm and guide them to food and water. Additionally, chicks are born with the instincts to automatically know how to eat and drink. Instincts will also help them to locate the things that will meet their needs. 
   • Note: If you are hatching live chicks, set up a brooder box with a heat lamp, food, and water as part of the party and discuss why these items are important parts of the chick’s habitat.
   • If you are not hatching live chicks, consider showing parts of a Chick Hatching video so students can observe chick behavior.
5. To finish up the project, go through the 21-day countdown and pictures again and ask students to recall the process. What were the most exciting parts? What did they learn about embryo development and living things? Now that the chicks have hatched, what physical traits will help them stay alive?

Activity 2: The Chicken or the Egg?

1. Using the school library, present three short informational texts: one on the life cycle of a plant, such as Pumpkin Circle: The Story of a Garden by George Levenson; one on the life cycle of the chicken, such as Chick Life Cycle by Elizabeth Bennett, and one additional text on the cycle of seasons, such as I Can Read About Seasons by Robyn Supraner. 
2. As you read each book, illustrate the cycle by drawing a picture or writing a word on the board to represent each step in the cycle and connecting the steps with arrows.
3. Compare the cycles on the board to other processes students may have observed. Life cycles of other species like dogs, insects, frogs, and cows may be appropriate, as well as weekly or daily schedules (wake up, go to school, go home, go to bed, wake up, etc.).
4. Discuss how farmers must work with the life cycles of plants and animals as well as the cycles of seasons in order to harvest a crop or produce a product like eggs. For example, at each stage in the life cycle of a chicken, farmers must provide different kinds of care. When the chick embryo is developing, the egg must be incubated at the right temperature and humidity. After the chick hatches, it needs a warm, clean shelter and food and water. As it grows, the chick needs more food and space. Once it is mature, a hen will start laying eggs. If the farmer wants eggs for people to eat, the hens need an environment with lots of light and a place to lay their eggs. If the farmer wants the eggs to produce new baby chicks, a rooster is needed to fertilize the eggs. Then, the cycle can begin again. 

Activity 3: I Have My Dad’s Beak

1. Using the first Parent/Offspring Card on Leghorns, compare and contrast the chick to its parents. On the board, make a list of similarities and a separate list of differences. 
   • Note: If you are hatching chicks from eggs, download a picture of a hen and rooster from that specific breed to use in this step. Many of the most common chicken breeds can be found on Wikipedia or through a simple internet search. Additionally, backyardchickens.com hosts photo galleries where users can post pictures of their own backyard flocks. 
2. As a class, look closely at the list of differences. Have students point out which differences they think might change into similarities as the chick grows up and which traits will stay different (if any). 
   • Examples of traits that change with maturity include size; feather color (sometimes), pattern, and length; and the shape and size of the beak (the egg tooth that a chick has at the time of hatching will disappear within two weeks). You may also want to note that the sound that the chicks make will change with maturity (chicks peep, roosters crow, hens cluck) or even play sound bites of chicks, roosters, and chickens to let students hear the differences. 
   • Examples of traits that will stay the same include eye color, wing shape, feathered legs, number of toes, foot shape and color, and any birth irregularities (note that this last item is an environmental trait, not inherited trait like the others).
3. Break the students up into groups and distribute one of the remaining Parent/Offspring Cards to each group. Ask students to discuss similarities and differences between the chick and its parents within their groups and to make a list of traits that change with maturity and traits that stay the same. Then, have each group make a brief presentation to the class. 

After conducting these activities, review and summarize the following key concepts:

• Inside of a fertilized chicken egg, a tiny embryo grows and develops over 21 days into a chick that can break out of its shell. 
• Over time, the chick will develop into a mature hen or rooster. Together a hen and rooster can produce a fertilized egg that will develop into another chick, completing the life cycle. 
• Different environmental conditions are required at each stage in the life cycle of a chicken. Farmers work with this cycle to produce eggs.
• Chicks, like all animals and plants, inherit traits from their parents.

1. http://www.incredibleegg.org/wp-content/uploads/wake-up-to-eggs-the-back-to-school-breakfast-of-champions-infographic_august_15_2012.pdf

• A Chicken Followed Me Home!
• All About Eggs
• Big Yellow Sunflower
• Chick Embryology YouTube Playlist
• Chick Life Cycle
• Chicken Embryo Development
• Chicken Genetics Matching Cards
• Chickenology
• Chickens on the Farm
• Chicks & Chickens
• Classroom Hatching
• Countdown to Hatch
• Farm Animals in a Box
• Farm Animals: Chickens
• From Egg to Chicken
• Hatching Chicks in Room 6
• Hatching Science Center
• Hatching Science: 21 Days of Discovery Video
• I Can Read About Seasons
• One Egg
• One Hen: How One Small Loan Made a Big Difference
• Parent/Offspring Cards
• Poppy's Chicks (Farm Friends)
• Poultry Reader
• Pumpkin Circle: The Story of a Garden
• Sonya's Chickens
• The Chicken-Chasing Queen of Lamar County
• The Life Cycle of a Chicken
• Tillie Lays an Egg
• Virtual Egg Farm Field Trips
• Zinnia and Dot