Ward, R. M.; Cranswick, P. A.; Kershaw, M.; Austin, G. E.; Brown, A. W.; Brown, L. M.; Coleman, J. C.; Chisholm, H. C.; Spray, C. J. Numbers of Mute Swans Cygnus Olor in Great Britain: Results of the National Census in 2002. Wildfowl 2013, 3-20.