Eggs across the animal kingdom range from simple to spectacular—even among the most common of barnyard animals, the chicken.
Our Weird Animal Question of the Week came to us via Danny Huynh, who asked: "My mom had a chicken coop with four chickens and they always lay eggs of different colors. Why are they of different colors?"
When it comes to chickens, the answer is genetics. There are over 50 breeds (check out the list on Oklahoma State's website), and their DNA dictates the color of the egg, says Jacquie Jacob, a poultry extension associate at the University of Kentucky in Lexington. (Learn more about heirloom chickens in National Geographic magazine.)
All eggs start out white, and any pigments are deposited during the egg's 26-hour journey through the hen's oviduct, according to Michigan State University.
What's more, you can often predict what color a chicken egg will be by the hen's earlobes. (You heard right—chickens have earlobes.)
A chicken breed called leghorn, for example, lays white eggs and has white earlobes, while chickens with red earlobes lay brown-shelled eggs. Jacob cautions there are exceptions to every rule: Lamona chickens have red earlobes, but their eggshells are white.
Araucanas lay blue-shelled eggs, and when you cross them with a breed that has eggs of a different color, that dominant blue-shell gene will make the resulting eggs blue, pink, or even green. (Now we just need some ham.)
Bright and Shiny
In wild birds, though, egg color often serves as camouflage. Take plovers, which lay eggs in sand and have sand-colored eggs, Jacobs noted.
"In Japanese quail, the speckling is a mechanism for camouflage," she said.
Mothers will find the ground that best hides the patterned eggs and lay them there. (Related: "Hunting for Quail Eggs? Mind Your Steps.")
An ostrich relative called the tinamou may have evolved turquoise eggs to attract other females and encourage them to lay their eggs nearby, creating a sort of safety-in-numbers strategy for avoiding predators, according to a 2010 study in the Journal of Avian Biology.
The tinamou's eggs are also as shiny as Christmas ornaments, a phenomenon that has long perplexed scientists—until now.
New research at the University of Akron reveals that tinamou eggs get their gloss from a thin, smooth outer layer on the eggs that contains various chemicals, according to a December 10 study in the journal Interface.
Works of Art
Birds fly right into our minds when we think of eggs, but other animals lay some amazing ones as well.
Insects, for instance, produce some work-of-art eggs—and also protect them beautifully. (See pictures of insect eggs in National Geographic magazine.)
The green lacewing, for instance, creates a silky stalk on which to hang its eggs, which keeps its offspring from predators—and cannibals.
One of the strangest examples we came across is the horn shark's egg case, which looks a bit like a natural drill bit.
George Burgess, an ichthyologist at the Florida Museum of Natural History, said the egg cases' spiral structures allow the female to wedge them into crevices, making it tougher for predators to get them. (Also see "Longest Living Octopus Found, Guards Eggs for Record 4.5 Years.")
Egg cases of elasmobranchs—a group that includes sharks, skates, and rays—are generally opaque, made of keratin, and can breathe.
Such "cases are not like the shell of a chicken egg. Water and oxygen go back and forth between them, and waste products are able to fuse out," Burgess said.
To avoid floating away, elasmobranch cases usually have tendrils that attach to a rock, algae, or some other anchor (moms don't stick around to keep watch).
Once baby skates hatch, their abandoned egg cases wash ashore, where beachcombers find them and sometimes call them mermaid's purses.
Now that's a legend that'd be tough to crack.