Hummingbirds are perhaps the most exquisite bird species because of their prominent iridescence, created by stacks of melanosomes in the feather barbules. The feather colours crucially depend on the nanoscopic dimensions of the melanosome, and the displayed iridescence can distinctly vary, dependent on the spatial organization of the barbs and barbules. We have taken the genus Coeligena as a model group, with species having feathers that strongly vary in their spatial reflection properties. We studied the feather morphology and the optical characteristics. We found that the coloration of Coeligena hummingbirds depends on both the Venetian-blind-like arrangement of the barbules and the V-shaped, angular arrangement of the barbules at opposite sides of the barbs. Both the nanoscopic and microscopic organization of the hummingbird feather components determine the bird’s macroscopical appearance.

This angle was measured on single barbs mounted at a rotatable stage attached to the MSP. The barb was rotated in steps of 5° around the position where the reflectance of the barbule was maximal. The barbule’s rotation angle followed from the position where the barbule reflectance was maximal with respect to the zero position, the plane containing the row of barbules.