Two songbird species show subordinate responses to simulated territorial intrusions of an exotic competitor

Abstract

Interspecific competition is rarely assessed between exotic and distantly related native species, although these can compete for some ecological resources. Here, we assessed the occurrence of interspecific aggression resulting from direct competition between two European native songbird species (henceforth focal species), the robin Erithacus rubecula and the blackcap Sylvia atricapilla, which are potential competitors for feeding resources and behaviourally subordinate to the exotic red-billed leiothrix Leiothrix lutea. In central Portugal, this exotic species lives in sympatry with robins and blackcaps at least since 2007. We used interactive playbacks to measure the behavioural response of blackcaps and robins towards intrusions by leiothrix and a submissive, native competitor — great tit Parus major. The singing behaviour of both focal species was affected by leiothrix playback. Robins exhibited a longer latency to sing, and both species avoided singing near the loudspeaker after leiothrix playback compared with great tit playback, which generally suggests a subordinate behaviour. Regarding changes in song parameters during the playbacks, only the peak frequency of blackcaps was affected by the playback. We discuss different possibilities for the origin of such submissive behaviour in native species.