Spotted Flycatchers are estimated to have declined by 59% across Europe during 1980–2005 (PECBMS 2007). A predator 'control' experiment has indicated that the abundance of nest predators may be determining the breeding success of Spotted Flycatchers, especially in woodland, where nest success was lower overall than in gardens (Stoate & Szczur 2006). Another study using nest cameras has identified avian predators, especially Jays, as responsible for most nest losses (Stevens et al. 2008). Decreasing survival rates may have been caused by deterioration in woodland quality, particularly leading to declines in the large flying insects that are food to the flycatcher, or by conditions either on the wintering grounds or along migration routes (Fuller et al. 2005).
Source: https://www.bto.org/birdtrends2008/wcrspofl.shtml