Environmental drivers of House Sparrow Passer domesticus presence and abundance in the Metropolitan Area of Barcelona: a multi-variant approach

Despite being one of the most abundant animal species in the world, House Sparrow Passer domesticus numbers have declined significantly worldwide in recent decades, above all in urban areas. We studied the influence of vegetation, urban structure, human activity and predators on the presence and abundance of House Sparrows in the Metropolitan Area of Barcelona (MBA), Catalonia, Spain. We established 80 point-counts in four land categories defined by urban location (intraurban, periurban) and urbanisation density (low, high) in spring and winter in 2015 and 2016. We used random forest models to analyse how presence and abundance were related to 22 explanatory variables. Our results highlight the complex interaction between structural and anthropogenic factors and House Sparrow presence and abundance. Presence increased with proximity to allotments and in areas with mid-level tree densities and no shrub cover; conversely, abundances peaked in areas with more litter. Predators and urban land-category had little impact on either House Sparrow presence or abundance. Neither presence nor abundance showed seasonal differences. Natural and semi-natural vegetation remnants and the heterogeneity of green spaces are crucial for the presence of House Sparrows in urban landscapes. As urbanisation becomes more intensive and homogeneous, these green spaces are becoming increasingly scarce, a factor that probably contributes to the observed declines in this sparrow’s populations throughout Europe. Human activity plays a critical role in its abundance, although any dependence on human-mediated resources may leave populations vulnerable in the event of changes in urban waste-disposal practices.