Davey, C.M., Vickery, J.A., Boatman, N.D., Chamberlain, D.E., Parry, H.R. & Siriwardena, G.M. 2010. Assessing the impact of Entry Level Stewardship on lowland farmland birds in England. Ibis 152: 474. doi:10.1111/j.1474-919x.2009.01001.x