biostudies-literatureLuepold SBSwiss National Science Foundationarae072https://www.ebi.ac.uk/biostudies/studies/S-EPMC11457480biostudies-literatureUnknown35(6)In this era of rapid global change, understanding the mechanisms that enable or prevent species from co-occurring has assumed new urgency. The convergent agonistic character displacement (CACD) hypothesis posits that signal similarity enables the co-occurrence of ecological competitors by promoting aggressive interactions that reduce interspecific territory overlap and hence, exploitative competition. In northwestern Switzerland, ca. 10% of <i>Phylloscopus sibilatrix</i> produce songs containing syllables that are typical of their co-occurring sister species, <i>Phylloscopus bonelli</i> ("mixed singers"). To examine whether the consequences of <i>P. sibilatrix</i> mixed singing are consistent with CACD, we combined a playback experiment and an analysis of interspecific territory overlap. ABehavioral ecology : official journal of the International Society for Behavioral EcologyA test of the mechanistic process behind the convergent agonistic character displacement hypothesis.PMC11457480179214Luepold SBPasinelli GCarlotti SfalseA test of the mechanistic process behind the convergent agonistic character displacement hypothesis.In this era of rapid global change, understanding the mechanisms that enable or prevent species from co-occurring has assumed new urgency. The convergent agonistic character displacement (CACD) hypothesis posits that signal similarity enables the co-occurrence of ecological competitors by promoting aggressive interactions that reduce interspecific territory overlap and hence, exploitative competition. In northwestern Switzerland, ca. 10% of <i>Phylloscopus sibilatrix</i> produce songs containing syllables that are typical of their co-occurring sister species, <i>Phylloscopus bonelli</i> ("mixed singers"). To examine whether the consequences of <i>P. sibilatrix</i> mixed singing are consistent with CACD, we combined a playback experiment and an analysis of interspecific territory overlap. A2024-01-01T00:00:00Z2024 Nov-Dec2026-06-02T23:14:19.216Z2025-04-19T19:23:37.78ZS-EPMC114574803938068810.1093/beheco/arae072