The Blackcap is a common and familiar bird over large parts of central and southern Europe. It is mainly migratory in the northern and eastern part of its breeding range. Increasingly in recent decades, however, it may be a short-distance migrant or resident in the west and south (Mullarney et al. 2000; Ehrlich et al. 2000).

Some Blackcaps now overwinter even in central and northern Europe, especially in urban and suburban areas (Aymi and Gargallo 2006). Fifty years ago, the Blackcap was considered a summer visitor to northern Europe and the British Isles. However, an increasing number of birds began overwintering in Britain and Ireland, in numbers growing from a few individuals in the early 1960s to the point where a recent survey of birdwatchers found that 31% of their gardens had Blackcaps visiting bird tables from October 2003 to March 2004. Work in the early 1990s showed that the birds overwintering in Britain and Ireland actually bred in south central Europe and that this newly evolved migratory behavior was associated with genetic differences. The main wintering areas associated with Blackcaps breeding in south central Europe (and therefore the ancestral wintering areas for the British and Irish birds) are southern Iberia and North Africa. The new wintering area is disjunct from the original, and birds wintering in Britain and Ireland display a completely different migratory orientation (Bearhop et al. 2005 and references therein). It has been suggested that the rapid evolution of distinct migratory pathways and wintering habits has been made possible by allochronic (i.e., differently timed) spring arrival of migrants from their respective wintering quarters resulting in assortative mating. In this scenario, individuals tend to mate with other individuals from the same wintering areas, which would facilitate independent evolutionary trajectories. Although differently timed spring arrival and the resulting non-random mating are likely important factors in the evolution of the new migration pattern, Rolshausen et al. (2010) concluded that differences in spring arrival dates are not sufficient to explain the observed degree of assortative mating.

Many Blackcaps from the eastern portion of their breeding range winter in sub-Saharan East Africa (Aymi and Gargallo 2006).