Since 1990, when the first Peregrine started breeding on a power plant in The Netherlands, the population has increased to three successful breeding pairs (raising 9 fledglings) in 1997. Many pairs used nestboxes specifically designed for Peregrines and placed at great heights on industrial buildings. It is advised not to supply nestboxes in power line support structures, because such sites are not safe for both falcons and men. Either falcons should utilise the available crow’s nests or nestboxes should be provided at large industrial buildings. Numbers of wintering Peregrines in The Netherlands have increased during the 1980s and 1990s. Records of display and copulations in spring do not necessarily indicate potential breeding birds, as many Scandinavian Peregrines do so before returning to their breeding grounds. Origins of wintering Peregrines, and therefore their chance of staying and breeding, can be checked by reading colour rings or checking for primary moult; the latter is completed in mid-September by Central European birds, and in November/December by Fennoscandian birds. Only Central European birds, especially those from the increasing population in Nordrhein-Westfalen, can be expected to settle as a breeding bird in The Netherlands.