Individual study: Effectiveness of broadcast of distress calls and use of pyrotechnics in deterring gulls Larus spp. from roosting at Farmoor Reservoirs, Oxfordshire, England
Gosler A.G., Kenward R.E. & Horton N. (1995) The effect of gull roost deterrence on roost occupancy, daily gull movements and wintering wildfowl. Bird Study, 42, 144-157
Daily movements of gulls Larus spp. between feeding and roosting sites can present a serious hazard to aircraft when these routes pass over airfields or airports. One way of reducing the risk of bird-strikes is to try to modify problematic flight-lines by deterring gulls from using certain roost sites. This study tested the effectiveness of the broadcast of gull distress calls and use of pyrotechnics in deterring gulls from roosting at Farmoor Reservoirs (51º45'N, 1º21'W), Oxfordshire, southern England, a winter roost site situated less than 10 km from a military airfield.
Three deterrence trials, each lasting three weeks, were carried out at Farmoor Reservoirs between late September 1990 and February 1991. During each trial, recordings of black-headed gull Larus ridibundus and herring gull L. argentatus distress calls were broadcast through a 15-Watt speaker. At the start of trials (when gulls were most persistent), a second operator also moved around the larger of the two reservoirs broadcasting distress calls from a 10-Watt portable unit. If playback failed to scare away gulls, one or more pyrotechnic bird-scare cartridges were fired towards them using a signal pistol.
Simultaneous counts of gulls at all known roosts in the area (including Farmoor) were carried out one evening per week during trials, as well as twice before the first trial and once after the final trial.
In the two weeks prior to the first trial, 10,430 and 8,270 roosting gulls were counted at Farmoor on the two survey evenings. The number of roosting gulls fell to 1,000 (with a further 8,000 visiting) on the first day of the first trial, and declined further to only one or two individuals by the end of the first week. Numbers of roosting gulls slowly increased to 4,500 during the four weeks between the first and second trials, but immediately dropped to zero at the start of (and then throughout) the second trial.
Following the end of the second trial, gull numbers quickly recovered, peaking at over 15,000 birds in late January. Numbers declined to zero again during the first week of the third trial, but deterrents failed to prevent roosting during the second week, when cold weather resulted in the freezing of a nearby alternative roost site.
Counts of gulls flying over the nearby airfield during the second and third trials provided some evidence for a reduction in numbers using the problematic flight-line.
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