Hatching

The hatching process of the eggs in James River Bridge is the highlight of this day. It's awesome that we can see and watch it so close.
But what is going on inside. How does that tiny creature get him or herself out of the eggshel, out of it's incubator. That is quite a job and don not underestimate the enormous lot of energy this must take. Making the escape is a proces that takes many hours. From the first pip to actually hatching can take over 12 hours.

About three days before hatching, the embryo's head burrows beneath the right shoulder so the beak is positioned under the wing & against the two membranes separating the embryo from the air space at the large end of the shell. Sometime that same day, due to oxygen depletion, the beak pierces through the membranes into the air space & pulmonary respiration begins.
The little chick is starting to make sounds as well, a very weak shri-shri-shri is coming from within the egg. From alle eggs that are in this stage. The little ones are telling eachother to hatch too, so all of them hatch after eachother with little time interval.

About a day later, with a dwindling oxygen supply, the embryo begins to kick, to twist and to thrust its head and beak backward, until the eggtooth pips the first hole. The chick can now draw breath. As fresh air enters the shell and circulates, the membranes inside begin to dry, and the blood vessels within those membranes begin to shrink. At this moment, both eggs in James River Bridge are in this stage.

The embryo continues to pip, kick and twist. Small cracks advance counter-clockwise by millimeters around the big end of the shell. A special "hatching muscle" on the back of the chick's neck swells to several times its normal size with a great influx of fluid from the embryo's lymphatic system. Testosteron is catalysing this. The swelling accentuates sensory signals sent through the neck, stimulating the embryo to further activity. Eventually, the cap of the egg is cracked enough. The embryo pushes it off, unfolds from the tuck, and escapes from the shell.