Global chromatic diversity of avian plumage: a comparative spectral analysis across geographic regions

Birds exhibit remarkable plumage colour diversity produced by various pigments and nanostructures, yet how plumage colour differs across major geographic regions is still not well understood. We compared 75,388 plumage reflectance spectra from seven geographic regions, computing colours for a human observer under standardised daylight illumination (D65). Across all regions, plumage colours predominantly ranged between orange and yellow hues, had similar lightness, and lined up along the daylight locus, following the same blue–yellow pattern as other natural colours. What changed from one region to another was the extent of highly saturated colours: with equal sampling effort, Africa and South America covered the largest gamuts and Europe the smallest. These differences likely reflect the uneven distribution of colour-producing lineages and ecological factors among regions. Our findings provide a comprehensive comparative framework for understanding global patterns of avian colouration and suggest that both evolutionary history and environment shape regional plumage colour diversity.