Dr. Universe – Eggs

  Is there any way to tell what color of eggs a chicken will lay? -Isabella, 8, Pullman, WA

Dear Isabella,

If you want to find out what color eggs a chicken will lay, you might just want to take a look at its earlobes. You read that right. Chickens have earlobes.

At first, I wasn’t even sure where I might find a chicken’s ears, let alone the lobes. And as a cat, working with birds can sometimes be a bit, well, awkward.

Fortunately, my friend Rocio Crespo offered to help out. She’s a Washington State University veterinarian who investigates diseases in birds, including chickens.

Crespo pointed out that a chicken’s ears are located on each side of its head, just below the eyes. Their ears don’t stick out like ours do, she explained.

“The ear is inside the head,” Crespo said. “It’s hidden behind some feathers.”

And the earlobe is just below the ear, marked by a slight thickening of the skin. It is bare of feathers. The earlobes can give us clues about the egg colors. Crespo said that if a chicken’s earlobes are white, the eggs it lays tend to be white.

After a bit of research, I discovered that all bird eggs start out white. But sometimes, while the egg is developing, certain pigments give the shell color.

Birds are actually the only animals that lay colored eggs. As you may know, some chickens lay brown eggs. If a chicken lays brown eggs, it is likely that she has red earlobes.

As usual, there are some exceptions to the rule. Some chickens with red earlobes may also lay greenish eggs or blue eggs.

While there seems to be an earlobe–egg correlation, scientists aren’t entirely sure why. But it might be because the genes that hold the instructions for earlobe and eggshell color are close together, Crespo adds.

Crespo said the key to really understanding egg color goes back to a bird’s genetics.

Scientists can learn more about birds as they look at the genotype, or the genetic makeup, of the organism. It’s like exploring a set of instructions for how an organism will develop.

They can also look at the phenotype, or the physical traits we can observe. For example, feather and eggshell color.

“It’s all part of the genetics,” Crespo said. “That’s part of why your skin is white or brown, or why your hair is red or blonde or black. It’s the same thing with the chickens. The egg color is part of their breed.”

Depending on the breed, a hen will lay about 500 eggs in her lifetime. And whether an egg is brown or white, it’s still the same on the inside. They taste the same and are equally nutritious.

A few readers have also been wondering which came first—the chicken or the egg. It’s a good question. But we’ll save that one for another time.

In the meantime, try making a bouncy egg and explore other experiments at pinterest.com/AskDrUniverse. Send a picture of your project to Dr.Universe@wsu.edu for a chance to be featured on askDrUniverse.wsu.edu.

Dr. Universe