Morphological basis for the waterproof characteristic of bird plumage

A surface variable, density of water-feather touching points （D_(p)） was proposed in this paper to express surface property of water repellency of contour feather. Tests in 29 species using breast contour feathers indicated that D_(p) was small in tericolous species, medium in wading and diving species, large in swimming species, with only a few exceptions. This implied that birds achieve appropriate D_(p) by optimizing the microstructure of feather to meet the requirement of water repellency. Therefore, D_(p) was a morphological marker linking structure and function of feather in studies of adaptive evolution of birds.