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)).