Use of falcons to displace nesting gulls from an urban area: final report

5. Results Summary

Falcons were flown without any target bird fatalities occurring throughout the deployment of non-hunting birds. The amount of airborne flying of falcons increased as the study progressed although some falcons showed a preference for the central steeple rather than flying around the Campaign Zone. Lesser Black-backed Gulls responded by exhibiting high levels of disturbed behaviour (either alert or taking flight) during the first half of the Campaign but this effect declined with time. Herring Gulls began to tolerate the presence of falcons whether in the air or perched on high buildings and any initial impact of falcons was largely masked by aggressive territorial behaviour exhibited within the Control Zone. Nevertheless, disturbance of both species was consistently higher within the Campaign Zone than the Control Zone.

Records of food stealing behaviour were observed on six occasions but not by project staff. Anecdotal evidence suggests that sub-adult birds were driven out of the Campaign Zone and three day-roosts were also lost. Nevertheless, compared to 2008 and the previous sequence of censuses, the number of breeding pairs was not decreased by the use of falcons under this regime. In fact, nesting populations increased. Possible drivers of this could be the destruction of nesting habitat at Cargenbridge, increases in return rates from previously successful years or displacement of birds from other colonies. The behaviour of gulls, particularly for the majority Lesser Black-backed Gulls, clearly showed that high levels of disturbance were achieved but that the impact of this reduced over time.