The species inhabits nearly all urban areas and is absent only in thinly populated open farmland, extensive forests and other natural habitats. Densities in rural areas are variable and only partly known in detail. Despite obvious colonisation of new towns and urban areas since the 1970s (e.g. reclaimed polders of Flevoland), hard evidence on the population development is lacking. A decline in the interior parts of old cities, caused by renovation or replacement of buildings, is partly balanced by redistribution of colonies over new districts. Perhaps some 30,000-60,000 bp in 1998-2000, but data on densities are rather insufficient.