Mute swan grazing on winter crops: Evaluation of three grazing deterrents on oilseed rape

The population of mute swans Cygnus olor (Gmelin) in the UK has increased since 1986 to >25 000 birds, leading to increased complaints of damage to winter crops, and the need for cost-effective management measures. Using a randomized block design in a split-field experiment, the effectiveness of three licensed grazing deterrents was evaluated for mute swans feeding on oil-seed rape: (1) a ziram-based chemical repellent (AAprotect TM at 10 kg ha -1 ), (2) white flags (25 flags ha -1 ), and (3) hazard warning tape (1000 m ha -1 ) with twine (400 m ha -1 ). Deterrents and control (no treatment) were assigned to one of four plots (approximately 1 ha) in each of four fields. From 4 December 1998 to 26 March 1999, grazing intensity was estimated by counting mute swan droppings on plots at approximately 2-week intervals. Over the entire study (10 - 15 weeks depending on field), total numbers of droppings did not differ significantly between treatments. Over the initial 8 weeks, however, droppings were significantly lower on tape/twine. Tape/twine may therefore potentially be cost-effective in reducing mute swan grazing, and further work is recommended to refine the technique.

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