Situation of red-billed Leiothrix (Leiothrix lutea) in Europe and interactions with native species

Abstract

During the last decades, the Asian-native red-billed leiothrix (Leiothrix lutea) has become established in Europe due to escapes or deliberate introductions. Despite a potential negative effect on ecosystems identified in other invaded regions, its situation in Europe and their potential effect on native birds are poorly known. We studied the behavioural and ecological relationships between leiothrix and the species composing the native bird community in central Portugal. We assessed which native species are more likely to compete for food (i.e., potential competitors) based on their structural size and diet composition (invertebrates and fruits). Our results showed that robin (Erithacus rubecula) and blackcap (Sylvia atricapilla) were the main potential competitors of leiothrix. We identified possible competitive advantages of leiothrix over its potential competitors considering its foraging morphology (e.g., a wider bill gape which promotes food swallowing). We also evaluated the role of behavioural dominance and aggressiveness on the establishment of leiothrix. We conducted a feeding experiment in a closed environment forcing dyadic interactions between a robin or a blackcap facing a leiothrix. We found that leiothrix were the initiators of the first interaction in most experiments, being apparently dominant over both native species.During the breeding season (spring), we used interactive playbacks to measure the behavioural response of blackcaps and robins (henceforth focal species) towards simulated intrusions by leiothrix. Leiothrix playbacks affected the singing behaviour of both focal species. Robins exhibited a longer latency to sing after leiothrix than after control playback. Both focal species avoided singing near the loudspeaker after leiothrix playback compared with control playback, which generally suggests a subordinate behaviour. Considering that our previous work indicated that leiothrix may displace some native species as result of its superior dominance, we decided to assess its distribution and population status in Europe. For that, we collected all public data available at citizen science databases and literature up to the end of 2017. We obtained records for 37 regions in 10 countries, and identified established populations in France, Italy, Spain, and Portugal. Its distribution range in Europe almost doubled in less than 20 years. A species distribution model showed that species presence probability increased with increasing combined values of human population density, spatial trend of occurrences, precipitation seasonality, precipitation of the driest quarter, and minimum temperature of the coldest month. Our results indicated high introduction rate near large urban areas resulting in a broad spread into adjacent forests. The establishment of leiothrix in natural habitats in Europe, and not in highly disturbed habitats as other invasive species, may constitute a new challenge for conservation.