Competitive advantages of the red-billed leiothrix (Leiothrix lutea) invading a passerine community in Europe.
The establishment of an introduced species is an important step of the invasion pathway. Often species become established because of their superior competitiveness over the native community or by occupying empty niches. Recently, the red-billed leiothrix Leiothrix lutea has become established in some European natural-woods, which can be quite relevant for nature conservation considering its position among the seven exotic bird species with highest negative impact in bird communities. We assessed which European-native species are more likely to compete with the leiothrix (i.e. potential competitors) based on their structural size and diet composition. Also, we evaluated the competitive advantages of the leiothrix, relatively to its potential competitors, that may allow its successful establishment, considering two approaches: exploratory behaviour and foraging morphology. Two species showed great similarity in structural size with the leiothrix, and also presented great similarity in diet composition, which makes them potential competitors: the robin Erithacus rubecula and the blackcap Sylvia atricapilla. The exploratory behaviour of the leiothrix did not differ from those of its potential competitors. However, the leiothrix presented more efficient foraging morphology than their potential competitors. Our results support the hypothesis of an establishment process by competitive advantage over native species rather than an opportunistic occupation of an empty ecological niche. The establishment of the leiothrix in European natural-habitats, and not in highly disturbed habitats as other invasive species, may constitute a new challenge for conservation.