Viewing geometry affects sexual dichromatism and conspicuousness of non-iridescent plumage of Swallow Tanagers (Tersina viriris)

GARCÍA, NATALIA C.; LOUGHEED, STEPHEN C.; BARREIRA, ANA S.; TUBARO, PABLO L.

AUK

AMER ORNITHOLOGISTS UNION

Año: 2016 vol. 133 p. 530 - 543

0004-8038

Some types of plumage colors are difficult to characterize spectrophotometrically since the properties of the reflected light change with viewing geometry (i.e. the relative positions of the light source, the observer and the orientation of the feather). This is the case of the non-iridescent plumage coloration of the Swallow Tanager (Tersina viridis), which seems to change from a human perspective as the angle formed between the light source and the observer vary. In this study we measured plumage reflectance with different angles of illumination and/or observation and used avian visual models to evaluate the change in sexual dichromatism and conspicuousness with viewing geometry from a bird?s perspective. We also calculated different color parameters to assess how these change with viewing conditions. Sexual dichromatism showed large changes with its maximum coinciding with the angle combination between illuminant and observer that produced both the highest conspicuousness for the males and highest crypsis for the females. Males? conspicuousness also varied with viewing geometry, and it was consistently smaller for the visual system of a potential avian predator (VS) than to conspecifics (UVS). The change in perceived coloration was mainly related to a large variation in hue and chroma in males? plumage as the relative angle between the illumination and observation probes changed. Our results show that viewing geometry can alter color perception, even for non-iridescent plumage coloration. Therefore, the relative position of the light source and the observer should be considered in studies of avian visual communication, particularly in species with plumage coloration as that of Swallow Tanagers.