Plumage Wettability and Feather Structure

Traditionally, the feathers of ducks and other water birds have been regarded as having attained excellent water repellency and this quality has often been ascribed to the properties of the oil from their uropygial gland. Although water birds produce relatively copious amounts of gland oil and spend much time preening, studies of the chemical and physico-chemical properties of gland oil have failed to show any unusual aspects that could explain this high water repellency. Early studies on gland oil were initiated by textile industries with the aim of developing new waterproofing agents for rain garments, leading to our present understanding of how porous structures including textiles and feathers repel water and resist water penetration. Modern studies seeking to understand the relationship between surface morphology, wettability, and droplet sliding in plants and insects as well as electron microscopy of biological structures such as butterfly wings have confirmed and expounded the original concepts that underlie the water repellency of rough and porous surfaces.