2.3 Ornament measurements
Both Kentish plovers and white-faced plovers exhibit sexually dimorphic plumage, with males displaying a black horizontal head stripe, two dark breast bands on each side of their breast, black eye stripes, and a rufous crown (Figure S1). Females, on the other hand, are paler and do not have dark markings (Figure S1).
To examine these plumage ornaments, we photographed each adult in three postures (dorsal and both profiles) in direct sunshine with a digital camera (SONY ILCE-6400). We photographed a scale, a white balance card (Kodak Gray Card 18% R-27), and a color checker (X-Rite ColorChecker Passport Photo). We concentrated on three different plumage ornaments: the male forehead stripe, the mask and crown, and the breast band. We used Adobe Photoshop CC (v.17.0.0) to measure the color and size of each ornament and adjusted each image for ambient light using the white-balancing tool and a white balance card as a reference. As detailed in the supplementary material, we used the relative difference of R in the RGB (red, green, blue) values to estimate the carotenoid-based red coloration (positively correlated), and the lightness (’L’) axis in the CIE (Commission Internationale de l’Eclairage) LAB color space to estimate the melanin-based plumage ornaments (negatively correlated). We discovered that this approach of quantifying plover ornaments was highly repeatable (for details, see Table S1 in the supplemental material, assessed using the rptR package (Stoffel et al. 2017)).