National mute swan survey 1990 /
Delany, Simon.
Greenwood, Jeremy J. D.
Kirby, Jeff.
Wildfowl & Wetlands Trust.
British Trust for Ornithology.
Scottish Ornithologists' Club.
Joint Nature Conservation Committee (Great Britain)
Peterborough : Joint Nature Conservation Committee,
1992.
"Report to the Joint Nature Conservation Committee by the Wildlife and Wetlands Trust, British Trust for Ornithology, Scottish Ornithologists' Club."
Mute swan.