How on earth do Delta students know how old a duck egg is? It seems pretty tricky since ducklings grow unseen inside an opaque eggshell.  One way to know how old an egg is to see exactly when a hen lays an egg, but as you could imagine, this would be pretty much impossible to do outside of a hatchery.  Instead, students use an old, but tried and true technique called ‘candling’.

By shining a light through an egg, researchers can see the shadow of the developing embryo.  Of course it would be much easier if the shadow actually looked like a duck, but a duckling starts out life as a few cells, and even when it gets bigger it is all folded up in the egg, so it looks more like a dark blob.  So, to figure out how old the egg is, researchers need to refer to special egg diagrams.

Any source of light can be used to candle an egg.  In the field, Delta students commonly use of a bit of radiator hose.  They hold the egg against one end of the tube, put their eye up to the other end and point it towards the sun.  This is enough light to see what is developing inside the duck egg.

You can try candling at home.  You will need an egg (a chicken egg from the store works just fine) and a flashlight.  Take your egg to a dark room or closet.  Hold the egg carefully and shine the flashlight through it.  If your egg is from the grocery store, you will not see an embryo because the egg was not fertilized. 

For pictures of candled eggs, visit the University of Nebraska-Lincoln web page at:

http://lancaster.unl.edu/4h/Embryology

or Mink Hollow Farms at:

http://pages.cpsc.ucalgary.ca/~becker/ HatchingProgram/Candling/ 

*** Please note that the federal government in both Canada and the United States protects waterfowl and most other wild birds. It is illegal to deliberately disturb a duck, goose or bird nest without a permit from the federal government. ***