The spread of the red-billed leiothrix (Leiothrix lutea) in Europe: the conquest by an overlooked invader?
The red-billed leiothrix (Leiothrix lutea) is an Asian-native passerine which has been introduced across several regions of the world, including Europe. Although it is widely considered to be among the most harmful bird invaders, its occurrence in Europe is still understudied. Here, we aim to assess its distribution and population status in Europe. We obtained records for ten countries distributed throughout 37 spatially independent regions. The species is already established in France, Italy, Spain, and Portugal. The distribution range in Europe almost doubled between the periods of 2000-2008 and 2009-2017. A species distribution model showed that leiothrix presence probability increases with increasing combined values of human population density, spatial trend of occurrences, minimum temperature of the coldest month, precipitation of the driest quarter and precipitation seasonality. We identified two main introduction periods: late nineteenth and late twentieth centuries. In 1997, the species trade started to be regulated, resulting in a reduction of the imported numbers during the following years. Thus, the recent increase of the distribution range may be mostly related with self-dispersion. There has apparently been a great introduction rate near large urban areas which resulted in a broad spread into adjacent forests. The relationship between climatic traits and leiothrix presence may be due to its feeding ecology, as it often forages in wet soil and is limited by the availability of fruits and invertebrates. Future climate change scenarios can add further uncertainty to the invasion process by the leiothrix in Europe.