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 ~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.