Deterring mute swans from fields of oilseed rape using suspended high visibility tape

Grazing by mute swans Cygnus olor can cause significant yield loss on individual fields of autumn-sown oilseed rape. In England, during 2002–2004, we tested the effectiveness of suspended high visibility tape in deterring grazing on 12 fields. On 8 fields tape was deployed over the whole field, whilst the other 4 fields were split into separate treatment (taped) and control halves (untaped). On all fields, trials involved sequential pre-treatment (no tape) and treatment phases (tape deployed), during which counts were conducted of swan droppings and swan numbers at approximately 2-week intervals. On all treated plots, following application of the tape, dropping counts were significantly reduced (median=99%, range 89–100%) as were swan numbers (median=97%, range=85–100%). The deterrent represents a highly effective control measure for reducing crop damage. In its current format, however, the technique is cost-effective only on the most heavily grazed fields.