Slechtvalken Falco peregrinus bezetten het Rijksmuseum en openen een bouwmarkt voor Gierzwaluwen Apus apus

In 2021 a pair of Peregrine Falcons nested successfully on Rijksmuseum (Amsterdam), using a nest box installed the previous year in one of the museum’s two historical towers. Eggs hatched during the first days of May. Two chicks (a male and female) were ringed on May 25 and these fledged around 18-22 June. From the first week of May onwards (arrival date), it was noticed that Rijksmuseum attracted increasing numbers of Common Swifts. The Swifts were apparently attracted by wind-blown feathers from pluckings of the Peregrines. The falcons plucked their prey on exposed ornaments of the two spires, which were also used as larders. Wind-blown prey feathers were captured by the Swifts in midair, and presumably used as nesting material. The inner city of Amsterdam holds a large Common Swift population. Plucking peregrines could attract up to several hundreds of Swifts, soaring above the historical centre and keeping an eye on the museum’s spires, in order to snatch a feather as soon as the opportunity presented itself. Mostly small, light downy feathers were captured, especially of Ring-necked Parakeets Psittacula krameri and Feral/Racing Pigeons Columba livia, the two main prey species of the Peregrine Falcons at Rijksmuseum. Apart from feathers from plucked prey, the Swifts occasionally also captured small moulted feathers of the adult female falcon and down of the chicks. Above the city, prey-carrying falcons were frequently followed by Swifts whilst attempting to snatch feathers that came loose of the falcon’s prey. Aerial feather collection was observed throughout the falcons’ chick stage, until June 25, with the largest number of Swifts visiting the museum reported during the second half of May/early June, coinciding with the swifts’ nest building and egg stages. This behaviour was most pronounced on days with fine weather. Strong winds did not hamper feather collection, but heavy rain did. It is likely that this behavior is widespread, as in the past decade Peregrines have colonised many cities in The Netherlands (the typical breeding haunt of Swifts), but has remained under-recorded. The high profile of this behaviour in Amsterdam is the result of a combination of a large Swift population, exposed plucking posts of Peregrines and high visibility (to human observers) of the falcons due to the relatively low position of nest and plucking posts. The price to pay for the Swifts is the chance of becoming prey of the falcons. In 2021, 5 out of 33 prey remains collected in the falcon’s nest box were Swifts, in other words the third most frequently captured prey species for this particular falcon pair.