Two male juvenile falcons in Uccle

The Peregrine brood at Saint Job church in Uccle consists of 2 males this spring.

It was by the ringing of the juvenile falcons, carried out today, that we could determine their sex. From the age of 3 weeks, the difference in body size between male and female falcons becomes evident. Females are larger and have less developed plumage than males.

During the ringing operation, the falcons are weighed, and their wings are measured in order to objectify the difference. The two from Uccle, who are now 27 days old, weigh and measure 675 g and 192 mm and 696 g and 199 mm respectively.

We can clearly see in the attached photos how the feathers are already well developed. The primary wing feathers (flight feathers or remiges) are not far from reaching half of their final size. The bluish “pipes”, which can be seen distinctly on the inner side of the wing, are the rachis. We could call them the “stems” of the feather. And if they are blue, it’s because they are full of blood! This blood provides the energy that will allow each feather to grow day after day until fledging. When the feather has reached its final growth, the rachis will no longer be irrigated and the feather will be “inert, composed solely of keratin.

The weight of the juvenile falcons is almost similar to that of an adult. In 27 days, the weight at hatching (around 30 g) will have multiplied by… 23! They will have gained an average of 24 g per day! But when will they stop growing?! Simple answer: now! The growth of the falcon chicks is almost complete. But what will they still do in the nest for a little over two weeks? Simple: now is the time for plumage growth. And that requires a lot of energy. Most of the food brought by the parents will therefore be “invested” in the growth of thousands of feathers which will allow these two falcon chicks to one day be among the fastest birds in the world!

Patience !