Bluebird and Small Cavity Nester Conservation
Sialis - Bluebirds and other small cavity nesters


How an egg hatches

Pipping. Photo by David Kinneer
Eastern Bluebird eggs - external pipping evident, newborn chick in back. Photo by David Kinneer.

If the egg is incubated, the embryo inside develops. The parent(s) periodically rotates and rearranges eggs in a nest to ensure equal heating. This also prevents the shell membrane from adhering to the shell, which could interfere with hatching.

  • First, circulatory, digestive and respiratory, and nervous systems start to differentiate.
  • Then limbs may begin to move.
  • An egg tooth is formed to help the bird break out of the shell when it hatches.
  • The yolk sac gets smaller. In preparation for hatching, the embryo is in a tucked position. It uses its bill to puncture the innermost shell membrane at the blunt end of the egg (called internal pipping.)
  • The embryo begins to breathe the pocket of air between the inner and outer shell membrane.
  • After a few more hours, the egg tooth is used to break through the outer shell membrane and the shell (called external pipping - see cracks and holes in photo above.)
  • When it penetrates the shell, the hatchling emerges from the egg.
  • The parents generally do not help the young get out of the shell, although they may watch intently. They may remove or eat the egg shell after hatching.

More information:

Pictures of bluebirds and other cavity nesters

Previous Pictures of the Week: © Original photographs are copyrighted, and may not be used without the permission of the photographer. Please honor their copyright protection. If you would like to use a photo for educational purposes, you can contact me.

I love the excitement of opening the box and looking inside not really sure what kind of eggs I will discover. Sort of like fishing in the ocean!
- Vicki Butler, Bluebird_L, 2006

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May all your blues be birds!

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Photo in header by Wendell Long.
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Last updated March 24, 2016. Design by Chimalis.