Effects of a new waste collection policy on the population of yellow-legged gulls, Larus michahellis, in the historic centre of Venice (Italy)

Urban sprawl represents one of the most critical threats to biodiversity leading to the decline of rare and specialist species and the proliferation of a few dominant generalist ones. Among the winners there is the yellow-legged gull, Larus michahellis, which has recently colonised towns, nesting on the roofs of buildings and feeding on urban waste by spreading the contents of garbage bags on the streets. This situation has been recently documented in the historic centre of Venice (Italy) where it led to negative environmental impact and serious consequences in terms of urban hygiene. To counter such problems, the public company responsible for managing the urban waste in the Venice municipality established a new waste collection policy in the city to prevent accumulation of rubbish in the streets and limit the amount of trophic resources available for the species. We performed a monitoring program of the urban population of yellow-legged gulls and used generalized linear models to investigate the effectiveness of the new waste collection system on reducing the amount of waste in the streets and its effect on the target species. Results revealed a statistically significant positive correlation between urban waste and gulls and a significant effect of the new policy in lowering these two variables. Open areas, strongly frequented, with food and beverage vendors and illegal dumps were also highlighted as the main contributors to the presence of yellow-legged gulls. Such information can be used by local authorities to plan specific interventions to reduce the attractiveness of the city to gulls.