Sympatric black-headed and elegant trogons focus on different plumage characteristics for species recognition

The ability of individuals to distinguish conspecifics from similar-looking congeners has important evolutionary consequences, yet few studies have determined which specific visual characteristics are used for species recognition, and whether closely related species use the same characteristics. In particular, sympatry with similar-looking congeners may influence which traits are important in species recognition. We presented elegant trogons, Trogon elegans, and black-headed trogons, Trogon melanocephalus, with models that closely resembled conspecifics and models that differed in either the colour of the belly, the colour of the upperparts or the tail-barring pattern, while broadcasting species-specific songs. Elegant trogons showed significantly more aggression towards the conspecific and tail models, suggesting that belly and back colour, but not tail-barring pattern, are important for species recognition in this species. In contrast, the black-headed trogon approached all models very closely, except for the conspecific model. We interpret this counterintuitive behaviour as reluctance to approach an unknown conspecific, suggesting that all three plumage traits are important for species recognition in black-headed trogons. Because the elegant trogon is not sympatric with a similar-looking congener, we argue that they may lack the ability to discriminate fine-barring tail differences or overlook this trait. Sympatry with the similar-looking violaceous trogon may have influenced species recognition in black-headed trogons, favouring the use of all three plumage characteristics, including tail-banding patterns, which differ between these species. Alternatively, it is possible that incongruent stimuli are attended to differently, with elegant trogons focusing on the acoustic traits and black-headed trogons focusing on visual cues. Nevertheless, our study provides the first experimental evidence that specific plumage patches are used for species recognition and that closely related species may use different traits for species recognition. Our findings also suggest that the presence of a similar-looking congener can influence which traits are important in species recognition. (c) 2016 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.