Breeding: Candleing

Once the eggs are laid the African penguins will incubate them for about 40 days. During those 40 days it is a mystery as to what is going on inside the egg. "Is the egg fertile?", "Is the chick developing inside?" If only we had x-ray vision.


An African penguin egg

Well, we don't have x-ray vision but we can use a technique called candling to help us get a glimpse inside the egg. Shining a concentrated beam of light through the egg to observe embryo development is called candling.


The candler

In a dark room, we hold the egg to the light of the candler to observe the contents of the egg. We will wait until the eggs are least 10 days old before we candle and check for development. The embryo appears as a dark spot surrounded by a faint outline of blood vessels that becomes larger as incubation progresses. Eventually only a dark mass and the air cell are seen before the hatch date.

Watch this video to see the candling process.

The first clip is of an egg that is about 10 days old. It is a fertile egg because we could see a tiny embryo (it looks like a kidney bean shaped dark mass) and blood vessels. Next you can see a fertile egg that is a little older, the embryo has grown (it takes almost half the space inside the shell). Sometimes at this stage you can actually see the developing chick moving inside the shell. The third clip is off an egg that is approaching its hatch date. As you can see the chick inside is so big that all you can see is a dark mass. The only space available is an air space that the chick will break through as it starts to hatch. The last clip is of an infertile egg. All that is visible is a yolk. If you held a chicken egg from your kitchen up to a light this is what it would look like as well.

Even with candling we still do not know 100% what is going on inside the egg so it is still exciting to wait and see how everything turns out. Stay tuned!

- Andrea