Effect of sympatry on discrimination of heterospecific song by varied tits

Abstract

Many animals recognize their own species through acoustic signals, and erroneous recognition incurs costs. Birds discriminate between conspecific and heterospecific songs; for example, male territory owners respond aggressively to songs of conspecific males within their territories, but not to heterospecific songs. This discrimination is affected by the costs associated with territory defence behaviours. In populations where birds live with a related species that sings similar songs, males may waste time and energy on useless territory defence behaviours if they mistakenly recognize heterospecific songs as conspecific ones. On the other hand, if males in allopatric populations recognize conspecific songs as heterospecific songs, they may risk losing territories because the songs are sung by conspecific rivals in the absence of heterospecifics. For this reason, the potential costs of erroneous species recognition are expected to differ between sympatric and allopatric populations. Thus, it can be hypothesized that, in species without interspecific territoriality, males in sympatry respond less strongly or not at all to heterospecific songs similar to their own, and males in allopatry respond equally to heterospecific and conspecific songs. In this study, I examined this hypothesis using varied tits, Poecile varius , in the Ryukyu Archipelago, Japan. Their songs are similar in structure to those of confamilial Japanese tits, Parus minor . I used song playbacks and evaluated the aggressive responses of 355 territorial males in seven populations of varied tits. Overall, varied tit males responded strongly to conspecific songs but only weakly to Japanese tit songs. Furthermore, responses to the heterospecific songs were much weaker in the sympatric populations than in the allopatric ones, which is consistent with the hypothesis tested. This study suggests that when secondary contact occurs, song discrimination may influence the effectiveness of territorial behaviours and the reproductive success of individual males from sympatric and allopatric populations. • I studied the effect of closely related species on song discrimination in birds. • I used playbacks of conspecific and heterospecific songs and compared the responses. • Male responses were weaker to heterospecific songs than to conspecific songs. • This effect was greater in sympatric populations than in allopatric populations. • Coexistence of related species may influence discrimination of conspecific song.