Q. When do hatching eaglets start to breathe? Is there air in the egg before they energetically work their way out?

A. The first breath comes three or four days before hatching, thanks to the small air bubble above the chick in the porous egg shell, said Amy Ries, who writes for the Raptor Resource Project, a preservation and educational project for all raptors. The project includes a webcam that records eagles nesting and breeding in Decorah, Iowa. Just before its first breath, the eaglet chick develops an egg tooth, a small, hard calcium spike on top of the bill. It is used to pierce the membrane that separates the chick from the bubble of air. This hole is called the internal pip. The chick gets a burst of energy with its first breath, Ms. Ries wrote on the project’s blog, and scratches a hole through the shell to the outside, called the external pip.

As more air comes into the shell, the chick starts the final process of hatching by vigorously scratching the inside of the shell in a circular path around the entire large end.