Quantifying iridescent coloration in animals: a method for improving repeatability

Widespread cryptic dichromatism and ultraviolet reflectance in the largest radiation of Neotropical songbirds: Implications of accounting for avian vision in the study of plumage evolution

“…Unlike what occurs with iridescent colors, the position of the feather relative to the observer and/or the light source does not qualitatively change the results for the coloration pattern described here. However, the use of a goniometer to fix illuminant and observer angles (such as those employed by studies of iridescent coloration) would help to improve the repeatability and standardization of color measurements across studies (Meadows et al 2011, Van Wijk et al 2016. Appropriate color descriptions, together with more knowledge about the visual context during the occurrence of sexual displays or signaling in the Swallow Tanager, will be crucial to understanding the functionality of structural plumage coloration with double scattering.…”

“…This is true for iridescent coloration, such as that observed in hummingbirds, the tail of male Indian Peafowl (Pavo cristatus), and the neck of some pigeons, for example, which varies in perceived hue as the illuminating and/or observation angles change in relation to the orientation of the feather (Prum 2006). To quantify variation in iridescent plumage that is biologically meaningful thus requires different measurement techniques (Osorio and Ham 2002, Meadows et al 2011, Van Wijk et al 2016. Most noniridescent structural feather colors show little or no variation in hue with viewing geometry under omnidirectional illumination conditions (Prum 2006); this is because light is reflected from the isotropic internal keratin structure of the feather in all directions equally (Saranathan et al 2012).…”

Dietary protein level affects iridescent coloration in Anna's hummingbirds, Calypte anna

“…For the crown and gorget, REF feathers that were not regrown during the experiment were also measured at the end. Our methods for achieving repeatable measurements from iridescent colors that change with small deviations in viewing geometry are detailed in Meadows et al (Meadows et al, 2011). Briefly, feathers were mounted on matte black art-quality cardstock and stored in glassine envelopes at room temperature until measurement.…”

Variation in Display Behavior, Ornament Morphology, Sexual Size Dimorphism, and Habitat Structure in the Fan-Throated Lizard (Sitana, Agamidae)

“…obs; see video S1a). Because the perceived coloration of iridescent surfaces depends on the angles between incident light, the surface, and the viewer (Prum, 2006;Meadows et al, 2011), rapid turning can ensure that most receivers will observe the iridescence, irrespective of viewing geometry, and may increase the conspicuousness of the signal. Research on the biomechanics of displays and the visual anatomy of signal recipients (Hebets and Papaj, 2005;Rosenthal, 2007) may reveal proximate explanations for the relationship between display behavior and ornament morphology in Fan-Throated Lizards.…”