The ULB falcon chicks have been ringed

It was ringing day on June 10 at the top of the tower of the Literature & Philosophy building of the Solbosch campus of the University of Brussels (ULB).

As a reminder, the peregrine pair started nesting there in mid-April, whereas normally it is at the beginning of March that the cycle begins. In question, a very probable first attempt, unsuccessful, on another tall building located nearby. As a result, 4 falcon chicks hatched between 24 and 25 May. A fifth egg didn’t hatch.

Weighing and measuring the wing length of each falcon is used to determine the sex. Among peregrines, the female is significantly larger than the male since in adult size, she weighs 1 kg, or even a little more! In the male, the weight is between 650 g and 700 g. But beware, the bird adult weight is reached at the first flight! So, at the age of 6 weeks in the case of peregrines.

The results of the measurements taken today on the 4 falcon chicks at the ULB indicate that the brood counts 3 males and 1 female this spring. The “sex ratio”, the scientific term for expressing the proportion of one category compared to the other, therefore leans towards males. And this is confirmed when we compile the data for the 7 broods ringed in Brussels this spring and whose chicks could therefore be measured and weighed. Out of a total of 25 falcon chicks, 17 are males, i.e. 68%! When looking at data over several years, and therefore over a large sample, the “sex ratio” is balanced. But this year, it is really surprisingly… unbalanced.

Back to the brood of the ULB. The female weighs 582 g and is marked with the black ring engraved with the code CXN. Males weigh 398g, 455g and 438g and are marked with the black bands CXJ, CXK and CXL respectively. Video 1 (which will be added very soon) shows the film of the ringing.

We also got the opportunity to clean the globe of the camera which was soiled by the faeces of the falcons. The image is therefore sharp and clear again. Unfortunately, it will only be for a few days. The falcons are going to do it again! Take advantage of it by then, because we will not disturb the brood only to carry out a new cleaning. Everything will be done to resolve the problem by next spring.

Next, and last stage of this 2022 season, the fledging of the ULB falcons is expected around July 5.

Since Wednesday, the 4 juvenile falcons of Woluwe-Saint-Pierre have left their nest. They are exploring on the balcony of the steeple. The camera therefore only makes it possible to observe them very occasionally. Streaming has therefore been cut… until next spring!

Video 1: The ringing film at ULB

Video 2: A falcon chick exploring around the steeple of Woluwe-Saint-Pierre