Birds exhibit remarkable variation in plumage patterns, both within individual feathers and among plumage patches. Differences in the size, shape, and location of pigments and structural colors comprise important visual signals involved in mate choice, social signaling, camouflage, and many other functions. While ornithologists have studied plumage patterns for centuries, recent technological advances in digital image acquisition and processing have transformed pattern quantification methods, enabling  comprehensive, detailed data sets of pattern phenotypes that were heretofore inaccessible. In this review, we synthesize recent and classic studies of plumage patterns at different evolutionary and organismal scales and discuss the various roles that plumage patterns play in avian biology. We dissect the role of plumage patches as signals within and among species. We also consider the evolutionary history of plumage patterns, including phylogenetic comparative studies and evolutionary developmental research of the genetic architecture underlying plumage patterns. We also survey an expanding toolbox of new methods that characterize and quantify the size, shape, and distribution of plumage patches. Finally, we provide a worked exampled to illustrate a potential workflow with dorsal plumage patterns among subspecies of the Horned Lark (Eremophila alpestris) in western North America. Studies of plumage patterning and coloration have played a prominent role in ornithology thus far, and recent methodlogical and conceptual advances have opened new avenues of research on the ecology and evolutionary origins of plumage patterning in birds.

These data were collected through digital photography. We processed RAW photographs using the image calibration and analysis toolkit, which is a plugin for ImageJ. We subsequently used R to perform a suite of downstream statistical analyses (PCA, boxplots) to characterize 'pluamge pattern space' in Horned Larks (Eremophila alpestris), as a worked exampleof how one can use new pattern analysis methods in ornithology.

These data include a data frame of plumage pattern characters following data processing with ImageJ and the Image Calibration Analysis toolkit. We've also included RAW format photos and the regions of interest that we generated using ImageJ.