At the end of the 1990s, Brussels ornithologists discovered a couple of peregrine falcons roosting on top of the cathedral's towers. In 2001, ornithologists of the Royal Belgian Institute of Natural Sciences (RBINS) in association with the (FIR); a French association dedicated to the protection of raptors, installed a laying-nest on the edifice in an attempt to encourage nest-building. This laying-nest was never used, but in the spring of 2004, a pair of falcons nested on a balcony on top of the cathedral’s northern tower. At the beginning of March, the female laid three eggs.
