Citation
Gilroy, J.J., Anderson, G.Q.A., Grice, P.V., Vickery, J.A., Bray, I., Watts, P.N. & Sutherland, W.J. 2008. Could soil degradation contribute to farmland bird declines? Links between soil penetrability and the abundance of yellow wagtails Motacilla flava in arable fields. Biological Conservation 141: 3126. doi:10.1016/j.biocon.2008.09.019