No falcon chicks in Woluwe-Saint-Pierre

The start of the continuous observations at the Woluwe-Saint-Pierre town hall dates from April 2. For reasons related to the COVID-19 setting dedicated by the safety council, it was not possible to start recording earlier.

On April 2, the Peregrine pair was incubating 4 eggs. As a reminder, the female is not ringed, so we do not know her age or her origin. This has been the case since 2014, the first year of nesting on this particular building overlooking the Woluwe valley and its magnificent Natura 2000 areas. Is it the same female as before? Maybe yes, maybe not. The male is well known, he was born in 2012 in the bell tower of the Saint Antoine Church located 3 km away. He's been in Woluwe-Saint-Pierre from the start. This is therefore, we can be sure on this, his 7th nest.

But here we are, May 7, and still no little falcons on the horizon. If we consider that by the most extreme of all chances, the couple started to brood on the day of the connection of the camera, hatching should have occurred early this week. And nothing yet. There is therefore no hope left in seeing falcons hatch in Woluwe-Saint-Pierre this spring. Flûte!

Obviously ... it's Nature. But no doubt, we would have preferred to admire the birth, the growth, the fledging of a new family.

However, we must now try to understand the reasons for this "failure". It is scientific curiosity, but also the urge to assess whether or not this lack of hatching is linked to a cause of human origin. A cause that therefore possibly can be prevented in the future. The program of scientific observation of Peregrine Falcons set up in Belgium in 1994 aims to monitor the evolution of the population of falcons, to identify possible - new or old - threats. "Falcon for all" stems from this scientific program. It was too much of an opportunity to share our observations with you and not only through scientific reports.

What can we propose as hypotheses? Would the adults be inexperienced? The male certainly is not. The female perhaps, since her age is not known. But any case of inexperience would have little influence on fertilization and/or brooding behaviour. We can also see that for a month, the two adults have been taking turns assiduously to incubate and turn their 4 eggs. Would the adults be then too old for the eggs to be fertilized / viable? In the case of the male, the hypothesis does not hold water; he is 8 years old. Prime time for a Peregrine. On the female, no info. So yes, maybe she is getting too old. But we don’t have any objective data to confirm this. Are the eggs unfertilized or are the embryos dead at one stage or another? That we will know! But then we should get the eggs and have them analyzed. At least, if the Peregrines do not evacuate them or do not eat their contents as we did observe in the cathedral! So, suppose we can get them and find that they were well fertilized, but haven't come to the finish. In this case, it will be necessary to have them analyzed in order to detect possible chemicals that could have contaminated them and ultimately kill them. But such analyzes do not always give results. Especially if the eggs have rotten in the meantime. Imagine a “dead” egg hatched at 37.7 °C for weeks. Not top! If they are not fertilized, they do not rot as easily. We should then conclude that there was a problem during fertilization and therefore during mating. And here we have perhaps a hypothesis which could be corroborated by a series of observations!

Regularly, the Peregrine pair of Woluwe-Saint-Pierre was attacked by an intruder. Once or twice, we know that it is a Peregrine because we see a silhouette in the sky, in the background. But most often, we see the male, the female, or both together, "furious" or worried in the nest or on the terrace, scanning the sky and yelling. Two videos attached show this behaviour filmed on Monday. No doubt that these attacks also concern "intruder" Peregrines. The behavior of the local couple is typical.

Peregrines are very territorial birds. Interference between couples can lead to deadly fights. At least 4 females - known to be the "defendants" of the territory because they are much heavier and stronger than males - have been found dead at the foot of a nest site in Belgium since the start of the season. Such cases have been reported almost every spring for some years now. This was the case at the cathedral in 2019. The blog "Murder at the cathedral" tells the story! (

The adults of Woluwe-Saint-Pierre are very much alive and are certainly able to defend their territory. But it seems that the frequency of attacks has really been very important this spring. Would a Peregrine or a couple of Peregrines claim this site which offers a magnificent view and therefore exceptional hunting possibilities? It may well be. But what does this have to do with unfertilized eggs? Simple. If the competition is indeed very strong, it could be that it has influenced the good progress of copulation and therefore the fertilization thwarted… Which would explain why we do not have a family of Peregrines in Woluwe-Saint-Pierre in the picture this spring? Hypothesis, but with supporting data!

The fact remains that the three clutches we are observing this spring are very special:  the death of the two falcons in the cathedral, the absence of hatching in Woluwe-Saint-Pierre and the disappearance of one of the 4 falcons from Uccle (dead in the nest or fallen?). One year is not the other!




Video 1: May 7, the female carefully turns the 4 eggs. It has been incubating since April 2 at least. There is no longer any hope of falcons to hatch.

Video 2: May 4, example of an attack by an intruder, most likely a Peregrine. The worried female protects her eggs. The furious male scans the sky.

Video 3: May 4 still, the male goes on the attack to defend his nest. The female follows him and leaves her eggs behind.