Model projections reveal a recent decrease in a Yellow-legged Gull population after landfill closure

Abstract

The food available in open-air landfills, one of the most common Predictable Anthropogenic Food Subsidies (PAFS), can have a profound impact on animal biodiversity. Understanding how and to what extent PAFS affect wildlife is crucial for a sustainable management of resources. Most large gulls behave as opportunistic foragers and constitute a good avian model to analyse the effect of PAFS reduction on animal populations. Using individual data from a Yellow-legged Gull population collected over a 15-year period we estimated survival and reproductive parameters and used them to parameterize an age-structured population model to explore the effects of the local landfill closure. Local survival probability declined with time as a consequence of the progressive closure of the local landfill sites. The top-ranked models included a quadratic function of time, suggesting an acceleration of mortality during the later years. An effect more pronounced in first year birds than in older birds. Population models predict a decrease of the population and confirmed a greater sensitivity of the population growth rate to adult survival probability. Overall, our results suggest that the reduced carrying capacity of the system resulted after landfill closures has caused a population decline which is expect to continue in the near future.