Harper, G.H., 1977. Preliminary report on analysis of results (Jan 1977) [of survey of nests in Herefordshire in 1974]. [Unpublished]., p.227.

Harper, G.H., 1977. Second report on analysis of results (Jan 1977) [of survey of nests in Herefordshire in 1974]. [Unpublished]., p.228.