Journey North Whooping Crane Migration

Is This Crane Egg Fertile and Alive?
By Sara Zimorski, ICF

An important part of captive breeding is finding out if eggs are fertile (holding a living embryo) and viable (capable of becoming a chick). Simple tests help us know.

Candling

We candle the egg to determine if it is fertile. Candling means holding the large end of the egg up to a strong light source while in a dark room. If the egg is fertile, you'll see a small light area at the large end of the egg, which is the air cell, and the rest of the egg will be dark. It is dark because of the developing embryo. What do you think it means if you see light all the way through the egg? (If you said the egg is infertile, you are correct.)

Floating

Floating an egg in lukewarm water makes it easier to see even tiny movement of the egg. Notice that a bit of the floating egg is above the surface of the water; that's the air cell. We use warm water so the egg stays warm.

We also play the brood call that a chick would hear from a parent. When an embryo is old enough (probably around 20 days old) it can hear the sound and respond enough that the entire egg will move. When an egg did not move, we learned it was no longer alive or viable.