Asymmetrical responses to multimodal signals in two Neotropical sister species of songbird

Animals communicate using various signal modalities, with signal structure and perception affecting mate choice and species recognition. While studies in birds have often focused on signals of a single modality (unimodal signals), birds frequently assess multiple signals simultaneously (multimodal signals). However, how females and males utilize multimodal signals in conspecific recognition remains understudied. In this study, we combined reciprocal playbacks with taxidermic mounts to investigate how two closely related species, the russet-naped wren, Campylorhynchus humilis , and the Veracruz wren, Campylorhynchus rufinucha , discriminate between conspecific and heterospecific multimodal signals (song and plumage) and to quantify the relative importance of each signal modality for conspecific recognition. We found an asymmetrical response between species, with russet-naped wrens responding significantly stronger than Veracruz wrens. Our findings align with the hypothesis of multimodal redundant signals, as both female and male russet-naped wrens displayed the most intense aggressive responses to the combination of conspecific song/mount female stimuli. Responses were intermediate when exposed to either conspecific or heterospecific song/mount and lowest when presented with heterospecific song/mount stimuli. In contrast, Veracruz wrens showed no difference in responses to any treatment, nor any sex-based differences. Both sexes of russet-naped wrens were able to discriminate between conspecific song/mount and heterospecific song/mount, regardless of whether the stimulus came from a simulated female or male intruder. In treatments with mismatched signal stimuli, both female and male russet-naped wrens exhibited a nonsignificant tendency towards stronger responses to conspecific songs from females and significantly stronger responses to conspecific songs from males, suggesting that songs might play a slightly dominant role in discrimination. Our findings suggest that both sexes of russet-naped wrens partially discriminate between species based on song and mount cues, while Veracruz wrens do not. Overall, this study sheds light on how multimodal signals are used in conspecific recognition and their implications in maintaining reproductive isolation . • We examined responses of two closely related wren species to multimodal signals. • Russet-naped wrens responded as predicted by the multimodal redundant signal hypothesis. • Veracruz wrens showed no difference in responses to any treatment. • Russet-naped wrens were able to discriminate between conspecifics and heterospecifics. • Song appears to play a major role in species discrimination for russet-naped wrens.