Though samples are too small to continue presenting a trend, CES data indicated a rapid long-term decline in productivity and there is evidence that survival rates have fallen (Siriwardena et al. 1998).
There is very little evidence available regarding the ecological drivers behind the decline of this species. In southern Britain, at least, the decrease may be attributable to a reduction in the amount of suitable young forest growth (Fuller et al. 2005). Amar et al. (2006) and Smart et al. (2007) both found relationships with lichen and bracken cover, although these studies were limited to broadleaved woodlands. Evans (1966) and Cramp & Perrins (1994) point to the importance of birch to the species, which could potentially explain the relationships found by Amar et al. (2006) and Smart et al. (2007). Birch seeds are an important component of this species' diet. Amar et al. (2006) state that birch has declined in many woodlands as they have matured, and this could raise the possibility of winter food as a factor in the species decline, although this evidence is circumstantial and given that species with similar winter diet, such as Siskin, are faring better, may be unlikely.
