How woodcocks produce the most brilliant white plumage patches among the birds

Until recently, and when compared with diurnal birds that use contrasting plumage patches and complex feather structures to convey visual information, communication in nocturnal and crepuscular species was considered to follow acoustic and chemical channels. However, many birds that are active in low-light environments have evolved intensely white plumage patches within otherwise inconspicuous plumages. We used spectrophotometry, electron microscopy, and optical modelling to explain the mechanisms producing bright white tail feather tips of the Eurasian woodcock Scolopax rusticola. Their diffuse reflectance was approximately 30% higher than any previously measured feather. This intense reflectance is the result of incoherent light scattering from a disordered nanostructure composed of keratin and air within the barb rami. In addition, the flattening, thickening and arrangement of those barbs create a Venetian-blind-like macrostructure that enhances the surface area for light reflection. We suggest that the woodcocks have evolved these bright white feather patches for long-range visual communication in dimly lit environments.

Automated summary

Until recently, it was believed that communication in nocturnal and crepuscular species mainly relied on acoustic and chemical channels, unlike diurnal birds that use contrasting plumage patches and complex feather structures. However, our study on the Eurasian woodcock revealed that these low-light birds have evolved intensely white plumage patches within their inconspicuous plumage for visual communication. The intense reflectance of the bright white tail feather tips is a result of a disordered nanostructure composed of keratin and air, as well as the flattening, thickening, and arrangement of the barbs that enhance light reflection.