Ward, R. M., Cranswick, P. A., Kershaw, M., Austin, G. E., Brown, A. W., Brown, L. M., … Spray, C. J. (2013). Numbers of Mute Swans Cygnus olor in Great Britain: results of the national census in 2002. Wildfowl, 3–20. Retrieved from https://tidsskrift.dk/Wildfowl/article/view/153878