There is strong evidence for a moderate overall decline of bird populations in the region (BirdLife International, 2017). A recent report (BirdLife International, 2015) shows that out of the 533 species breeding in the EU-27 countries, 153 have declined since 2001, while 136 show a long-term decline (since 1980, Table 3.6). Most of the large-scale,long-term research studies (Gregory et al., 2007; Jørgensen et al., 2016b; Reif et al., 2008; Vickery et al., 2014) as well as many smaller studies (e.g. Vilkov 2013) also report declines in either species richness or populations. However, different species groups and regions exhibit different trends, and knowledge gaps exist. Notably, population sizes are unknown for many species, particularly in Eastern Europe and Central Asia (BirdLife International, 2017).