Proximate and ultimate causes of the variable structural color in the Swallow Tanager (Tersina viridis)

SKIGIN, D.; BARREIRA, A. S.; AMBROSIO, C.D.; TUBARO, P. L.; INCHAUSSANDAGUE, M.

Dresden

Workshop; Bio-inspired Optics and Photonics - From Metamaterials to Applications - International Focus Workshop; 2019

MAX PLANCK INSTITUTE FOR THE PHYSICS OF COMPLEX SYSTEMS

The Swallow Tanager is a common and sexually dichromatic passerine living in the canopy of the Neotropical forests. Males and females are blue and green, respectively. Male?s plumage reflectance spectra change significantly depending on the relation between the angles of incident light and observation, irrespective of the orientation of the feathers, turning from blue to turquoise-green. We investigated the physical basis of this phenomenon using the Korringa-Kohn-Rostoker (KKR) method to simulate the electromagnetic response of the quasi-ordered nanostructure present in the feather barbs, under different angles of incidence and observation. We measured the size of the air spheres present in the barb?s medulla and its variation using TEM images and employed this information to feed our analysis. In this way we obtained an electromagnetic response strongly dependent on the relation between the angle of incidence and observation that matches the variation observed in the plumage of male Swallow Tanagers. We discuss the functional implications of these changes upon the degree of sexual dichromatism perceived by the birds as well as on the contrast of plumage color against a forest background.