Seed Dispersal by an Invasive Exotic Bird in Europe

Native birds play a critical role in seed dispersal. The introduction of a new species may result in unpredictable effects on an ecosystem, namely in terms of seed dispersal. The Red-billed Leiothrix Leiothrix lutea is a frugivorous species native to Asia, whose potential role as seed disperser has not yet been analysed in its introduced range in Europe. We compared the role of Leiothrix with that of Eurasian Blackcap Sylvia atricapilla and European Robin Erithacus rubecula, which are among the native species with seed dispersal roles in Europe. We compared seed expelling behaviour among species (defecation or regurgitation of seeds), which can potentially shape seed dispersal, depending on whether the seeds germinate following expulsion. Field work was conducted in Central Portugal between November 2014 and January 2015 and included bird captures to collect faecal samples, followed by faecal analysis to check for the presence of seeds. We also surveyed plant species abundance and fruit availability in the study site. The feeding and seed defecation behaviour of Leiothrix closely matched that of Robins, as most individuals of both species consumed fruits without ingesting seeds and their faeces mainly contained plant material and few seeds. On the contrary, more than half of Blackcap faeces contained seeds. All three species ate similar plant species. Although Leiothrix faeces indicate that this species primarily eats fruits without ingesting seeds; a small fraction of faeces samples (c. 13%) contained seeds. Our results suggest that Leiothrix has low potential to be a seed disperser in Central Portugal and probably elsewhere.