The sole hatchling of the cathedral.

A first chirp is heard on April 12 at dawn at the cathedral. Forty-eight hours later, a first falcon hatches. It’s down still wet, it briefly shows itself for our admiration. This is the fifteenth year in a row that a pair of peregrine falcons nest in the heart of Brussels, at the top of the north tower of the Cathedral of Saint Michael and Saint Gudula.

The first will unfortunately also be the only hatchling of 2018, at the cathedral. Since it came out of its shell, there has been no more hatching. One chick almost matured, but died while still in its egg shortly before hatching. Why ? It is impossible to determine with certainty, but two hypotheses can be proposed. Either he was simply not viable and did not have the strength to get out of his shell. Or it could have been an accident: during the process of hatching, the shell could have been somewhat damaged by a movement of one of the adults. The shell in the damaged area then crumbles, like it would when you peel a hard-boiled egg. Just as is the case with your hard-boiled egg, the pieces of shell do not come away, but stay attached to the membrane – this is what you can see several times in the video clips. Why doesn’t the falcon get out of the egg in such circumstances? Simply because to pierce the shell from the inside of the egg, the chick must find a foothold to support itself so it can exert the greatest force possible with its beak. If the shell is crumbled, the surface of the egg is no longer hard and the falcon can not use it to leverage itself.

In such circumstances, adults never help a chick out of the egg. It's the chick who has to do it alone. Why? Probably to let natural selection run its course. Attempting to save a falcon which is not able to get out of its egg on its own, would not make sense : this failure to extract itself would indicate that the bird only has a very poor chance of survival. This is a hypothesis of course, but often verified, including in farmed birds.

An egg whose shell has apparently been partially damaged, we’ve encountered it during the 2016 nesting season as wel. The female Peregrine then carried the egg in question outside her nest. Same thing this year! Incredible behaviour, but again logical. It is clear that the female realizes that the falcon inside the egg has died. She knows on the one hand that there is no chance that it will hatch (obviously ...) but above all, she is able to realize that leaving it in the nest is likely to create a cesspool of infection. It must therefore be evacuated, just like left-over prey.

Two eggs remain, showing no signs of damaged shells or early hatching. They are either non-fertilized or dead during incubation. Yet they haven’t been taken away by the female! It certainly does not represent a risk in terms of infection on the one hand. On the other hand, does she still hope that they will hatch? Probably so.

A single hatchling on 5 eggs laid, obviously it’s not much. But that’s nature for you. Recall that we are observing wild birds!

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