Night vision

The peregrine falcon is a diurnal bird. This means they are active during the day and not at night, like owls for example. That does not mean that the falcons sleep all night deep, or that their behaviour cannot evolve.

When the sun goes down and Brussels is bathed in a bright glow, the balcony camera automatically switches to infrared (IR). The images are then no longer filmed in colour, but are shown in black and white. This way, it’s not necessary to focus a spotlight on the nest to observe the behaviour of the falcons and their parents at night. These infrared films are always of high quality. They allow to observe the falcon in other colours, and with different contrasts as compared to the images in colour. Thus, we can observe that the eggs of peregrine falcons exhibit a striking reflection, since they don’t appear dull at night (brick red in normal light), but brilliant white (see the video!). It was already known that the eggs of birds that nest in cavities (so often in the dark) have a strong reflection. It’s assumed that this allows the birds to locate their eggs more easily. Is this also the case for the peregrine falcon?

The nocturnal observation of the nest shows that the adult female remains close to her falcons. Currently - the falcons are now 2 weeks old - they are still covered by her. Soon they will be too big, but she will always be around, stationed on the platform or between the pilasters of the balcony.

The falcons regularly wake up during the night. They rotate themselves, move a bit, and go back to sleep. At night they are rarely fed, but it happens. It seems that their nocturnal activity increases with age.
The biggest discovery of the nocturnal behaviour of peregrine falcons, is that they also hunt in the dark! This was first proved by British colleagues at Derby Cathedral at the end of the 2000s. In Brussels, this nocturnal activity was already suspected in 2004. Remains of prey (feathers, carcasses, and skulls) were discovered at the base of the tower, often nocturnal migratory birds. These were indirect findings.

The new camera that was installed in the St. Michael and Gudula Cathedral now allows us to directly and precisely observe that the male returns from hunting, poses itself on a gargoyle, and begins to plume his prey conscientiously. This does not last all night, you need to connect at the right time, but the observations are surprising!

To be continued... in the next blog!