Image processing
We used the MICA toolbox in ImageJ v1.52k to linearize, align, and combine our paired VIS and UV photographs into a series of multispectral images (Schneider et al. 2012; Troscianko and Stevens 2015). We used the 10% and 77% reflectance standards to linearize the images, and each of the photo pairs were aligned manually. We then manually selected regions of interest (ROIs), from each multispectral image, by selecting up to six of the strongest UV reflecting regions (UV+), and up to six similarly sized and shaped adjacent regions that did not reflect UV (UV-).
For the butterflies, we selected ROIs from the undersides of both the forewings and hindwings as these regions will be visible to both predators and conspecifics, and where most species had the greatest UV reflectance. In the frogs, the location of the UV reflecting regions was more variable but was limited to dorsal, lateral and inguinal regions which would similarly be visible to avian predators. All ROIs were also chosen to avoid regions of specular reflectance (see Figure 1 for species-specific UV reflection regions).