Analysing citizen science data to address the demographic expansion of the Eurasian Magpie (Pica pica) in southern Spain

Abstract

Citizen science platforms such as eBird provide essential spatiotemporal information and big data for the study of birds. The analysis of an extensive 20-year dataset of the distribution of the Eurasian Magpie Pica pica showed that the species is steadily expanding within urbanised areas in the south of the Iberian Peninsula. The occurrence of the species in the eBird checklists in the study area has an average exponential growth rate greater than 20%. The area occupied by the species has multiplied by 40 in the last 20 years, going from 25 to almost 1000 km2. In order to test potential negative impacts of this demographic expansion on potential Magpie prey species, such as other birds, a seasonal study of the Magpie’s diet through pellet analysis showed that its stable diet consists of insects, snails and seeds, while other birds or food from anthropogenic sources does not constitute a significant part of its diet. The combined use of new open-science big data technologies together with classical monitoring and laboratory study offers indispensable tools for the assessment of species distribution and potential spatial management.