Hatching in progress in Woluwe-Saint-Pierre!

The female, nesting at the top of the tower of the City Hall of Woluwe-Saint-Pierre this spring, laid her first egg on March 8, the second on March 10, the third on March 13 and the fourth on March 16. A clutch of 4 eggs corresponds to the normal maximum for a female peregrine. The "abnormal" maximum, let's say rather exceptional, is 5 eggs.

Classically, a female peregrine lays one egg every 48 hours - the time it takes to form it in the bird’s body. The female of Woluwe-Saint-Pierre did indeed lay her first two eggs on a 2-day interval, but between the third and fourth, the interval has been around 3 days. Nothing to worry about, but we witness that in nature there is the norm and then, often, the reality, depending on the physical condition of the individuals, the availability of prey, the weather ... The process of egg-laying represents an important expenditure of a falcon’s energy. A peregrine's egg weigh on average 50g, so the female of Woluwe-Saint-Pierre "produced" the equivalent of 200 g or about 20% of her body weight. Only in 8 days!

Incubation follows, of course, just after egg-laying. For peregrines, it takes 32 days of incubation, beginning from the penultimate egg.  This was also the case here, since both parents have been covering the four eggs since March the 13th, they relayed each other. In peregrines, male and female share breeding time. However, females have a more important role than males. She broods normal all night and about two-thirds of the day. Here too, behaviour might vary, probably according to individuals. It is the incubation, at 37.7 ° C, which will allow embryonic development until the moment that, completely formed, the young bird will pierce its shell. And that’s what is happening now!

Today at the end of the afternoon, after 33 days of careful brooding, the hatching process of the eggs is initiated in Woluwe- Saint- Pierre!  This is the fifth consecutive year that peregrines nest in the tower of the City Hall. And it's always an emotion. The hatching is a crucial phase of the nesting process. Extracting the shell is a considerable effort for the chick. He must first tear the membrane in which he was locked for over 4 weeks. This gives him access to the air cell, a ‘’bag’’ filled with air, located at the egg’s larger end. The chick then begins to breathe for the first time. Quickly, he then pierces the shell, he needs fresh air! But he is still really trapped in the egg, and now it's time to get out! The last step is to shear the shell perfectly to "decapsulate" as is done to eat a boiled egg. But obviously without a knife and from the inside! Without a knife yes, but not without tools! There is a very hard protrusion, called "egg tooth" or "diamond" at the end of the beak of the chick. And because of this, he will be to cut the shell so well. An achievement that will be done in 2 stages: first he will make a circular cut; then he will push it until it “jumps of". An achievement that every bird, from goldcrest to ostrich, must realise!

Last peculiarity: during the whole process of hatching, even before the piercing of the shell, the chick and his parents are communicating vocally! Chirps, cheeps and little calls follow each other, as illustrated in the video (next to the blog), taken at another breeding site this spring.


Photos next to the blog:

Photo 1: the male is breeding, we can see very well the pierced egg.

Photo 2: The female relays the male, at the very delicate moment of hatching

And the video!