Patterns in the relationship between water repellency and feather structure

Water repellency of individual feathers and three macroscopic structural characteristics (percentage of plumulaceous structure, shaft curvature, and feather mass) were examined in dorsal and ventral contour feathers from 59 species of birds in 15 orders. The primary objectives were (1) to examine the variation in feather structure and water repellency throughout the Class Aves; (2) to investigate relationships between repellency and macroscopic feather structure; and, (3) to address problems associated with reestablishing repellency in birds which have been contaminated, particularly in oil spills. Water repellency was quantified using water retention as an index, followed by a "detergent test" measuring the feather's resistance to water penetration. Feather structure was examined qualitatively with scanning electron microscopy and quantitatively by measuring surface areas, shaft curvature and mass. Dorsal and ventral feathers were significantly different (p ;Structurally, curvature was most predictive of repellency overall, but mass was important in aquatic species, whereas plumulaceous area was important in non-aquatic species. Feathers of non-repellent individuals of aquatic species were less curved and lighter than those of their repellent counterparts, and in many cases appeared worn or contaminated. At least two aquatic species retained water primarily in the open pennaceous structure with the least in the plumulaceous region, although the coherent vane was more resistant to penetration.;Cleaning of oil contaminated birds produced little mechanical feather damage. Feathers from cleaned individuals failing to regain their repellency exhibited contaminating residues disrupting the microscopic structure. These highlighted the importance of thoroughly cleaning and rinsing affected birds, along with providing appropriate rehabilitation facilities in order to aid restoration of water repellency in captive birds.;Feathers within the same taxon were generally more similar to each other than to feathers from other taxa. These patterns were overlaid, however, by characteristics related to the aquatic behavior of species. Branta sandvicensis, non-aquatic birds, were more like other Branta than like other non-aquatic species, but they were simultaneously more like other non-aquatic species than were any other Branta. Similarities in structure and repellency were also found among diving species despite their taxonomic differences.