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Adapting strategies to maintain efficiency during a cull of yellow-legged gulls

Lookup NU author(s): Dr Pete Robertson



Abstract: Increasing populations of yellow-legged gulls (Larus michahellis) in theMediterranean have created con􀃀 icts with seabird conservation, migrating raptors, andhumans. As a mitigation measure, gulls are routinely culled in the region. Previous studiesof extended culls show that catch per unit effort declines over time through a combination ofpopulation reductions and avoidance behaviors developing within the remaining population. Wecountered these problems during a 4-year cull of yellow-legged gulls in Gibraltar by matchingthe type and mode of deployment of 􀂿 rearms in response to changes in gull distribution andbehavior. We found that shotguns were effective when gulls mobbed operators near nestingareas, while ri􀃀 es were more effective as gulls became wary and retreated farther from theoperators. Changing the type of 􀂿 rearm enabled us to counter the expected rate of decline inculling ef􀂿 ciency throughout the project. We were most ef􀂿 cient in the 􀂿 rst year of the project,killing gulls at a mean rate of 8.35 birds per man-hour. Although this declined to 4.83 by thethird year, the adjustments that we made to the way 􀂿 rearms were deployed raised it to 6.4in the fourth year despite a 79% decline in the observed total gull population over this period.We modelled the population data collected using a Leslie Matrix to evaluate the impact ofmanagement at the end of the culling period. The population declined at a greater rate thanexplained by the numbers actually culled, suggesting that the cull resulted in an additionaldisturbance, which triggered emigration at a rate of 35%, over and above the numbers culled.

Publication metadata

Author(s): Roy S, Ridley R, Sandon J, Allan J, Robertson P, Baxter A

Publication type: Article

Publication status: Published

Journal: Human-Wildlife Interactions

Year: 2016

Volume: 10

Issue: 1

Pages: 83-90

Online publication date: 10/05/2016

Acceptance date: 02/04/2016

Date deposited: 10/05/2016

ISSN (print): 2155-3858

ISSN (electronic): 2155-3874

Publisher: Berryman Institute