Citation
Gregory, R.D., Noble, D.G., Robinson, J.A., Stroud, D.A., Campbell, L.H., Rehfisch, M.M., Cranswick, P.A., Wilkinson, N.I., Crick, H.Q.P. & Green, R.E. 2002. The State of the UK's Birds 2001. RSPB, BTO, WWT, JNCC, Sandy, Bedfordshire