Illustrations of handbook of the birds of the world: Datasets of RGB values and color classification of birds

Plumage color, an important trait of birds, has been widely studied from
the perspectives of taxonomy, macroevolution, biogeography, and behavioral
mechanisms. However, quantifying avian plumage color remains challenging,
and data on the classification and proportion of plumage colors at the
species or subspecies level are rarely reported. Some studies have
examined plumage colors using illustrations from bird field guides, and
hand-drawn illustrations have been shown to be an effective and rich
resource for retrieving plumage data in large-scale ecological and
biological studies. Here, we collected all illustrations from Handbook of
the Birds of the World Alive (HBW Alive) and quantified them as RGB
values. HBW Alive includes scientific illustrations of more than 10,000
species and subspecies on a uniform white background, which facilitates
plumage quantification. We extracted RGB values from each image, excluding
the white background, and applied the K-means clustering algorithm to
categorize plumage colors into 24 groups. The complete datasets comprise
18,757 illustrations of 10,290 bird species, with RGB values of 1,000
pixels and the proportion of 24 colors recorded for each image. This
dataset includes 5,288 subspecies, male and female plumages of 2,618
species, and more than two morphs for 456 species. Although illustrations
have inherent limitations in capturing subtle color variations, this
comprehensive dataset provides a valuable resource for investigating
ecological, evolutionary, and biological questions across scales, such as
species divergence, phenotypic variation in response to climate change and
human activities, and global patterns of avian biodiversity. The datasets
are not copyright restricted and we encourage researchers to cite this
paper when using them in publications.