More than expected: the abundance of yellow-legged gulls Larus michahellis breeding in the historic centre of Venice and the initial effects of the new waste collection policy on the population

Yellow-legged gull, Larus michahellis, has undergone widespread colonization of the urban environment in recent past. Starting in 2000 this affected the historical centre of Venice, 24 roof-nesting pairs being recorded in 2005, with this number increasing significantly in the last decade. In 2016, the waste management company of Venice established a new door to door garbage collection system to prevent the accumulation of rubbish in the streets and limit the trophic resources available for the species. The study provides an up-to-date estimate of the urban population of yellow-legged gulls, using Distance Sampling method. We also studied the effect of the new system on the species by comparing the population estimate before and after the change and by analysing the trend of individuals collected in the old town by the service of wildlife recovery during 2010-2018. Results estimate 440 breeding pairs (95s% confidence interval: 326-593) in June 2018 and show a 34% decrease of breeding pairs in 2018 with respect to 2017, as well as a decrease in number of 1-year birds and pulli collected by wildlife recovery service starting from 2016, year of the policy implementation. Our data did not show a significant decrease in the overall number of individuals, suggesting the new policy has a stronger effect on the breeding success of the species than on adult survival. This study emphasizes the importance of preventing rubbish accumulation in the streets as factor for reducing the abundance of urban yellow-legged gulls.