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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.
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
URL: http://www.berrymaninstitute.org/files/uploads/pdf/journal/spring2016/AdaptingStrategiesRoyEtal.pdf
