Arie M. Rijke

By Arie M. Rijke

The structural details of the flight and contour feathers of seabirds closely match the requirements of their habitats and feeding habits. They serve a variety of functions ranging from intraspecific signaling to such physical qualities as thermal insulation, water repellency and resistance to impact. It comes as no surprise, therefore, that they are composed of an array of elements that confer these qualities to the optimal benefit of their avian bearer. In this chapter, the physical bases for these functions are provided in both mathematical and evolutionary terms. Some functions excel at the expense of others, and many species have evolved an optimal balance between functions in terms of both feather microstructure and behavioral patterns that suit their specific habitat and feeding habits. The effects of mechanical forces on feathers are presented in terms of the impact of diving, plunging and alighting, and the structural properties in seabird feathers identifiable as adaptations to these forces. Finally, the way oiling affects the water repellency and resistance of feathers is discussed. It is concluded that the flight and contour feathers exhibit morphological and mechanical features that are advantageous for specific habitats and feeding techniques.

Part of the book: Seabirds

By Roelof D. Coertze and Arie M. Rijke

Water birds have contour feathers in contact with water that show in their distal one-third adaptations to water repellency, resistance to water penetration and forceful impact with water. These qualities vary according to their intimacy with open water. In this study, the geometry of this part of the feather was examined to detect additional features that would affect viscous drag in water. The length-to-width ratio was measured and used to calculate the viscous drag coefficients for 48 water birds and, for comparison, 12 land birds. The lowest values for the drag coefficient were observed for birds with foraging niches as diving and swimming, followed by plunging, surface feeding, aerial and ground feeding. Land birds with no open water in their habitat had the highest drag coefficients. Three statistical approaches were used to validate the results. Allowing for the phylogenetic relatedness of the 60 species obscured any significant differences that may exist, but a non-parametric analysis that does not assume the conditions of equal sample size and variance turned out to be the most appropriate method for our data set.

Part of the book: Birds

By Arie M. Rijke

The structural details of the contour feathers of water birds are known to serve a variety of functions ranging from intraspecific signaling to such physical qualities as thermal insulation, water repellency, resistance to impact and viscous drag reduction. All of them closely match the requirements of habitat and feeding habits. It comes as no surprise, therefore, that contour feathers are composed of an array of elements that confer these qualities to the optimal benefit of their avian bearer. In this chapter, we review the physical bases for these functions expressed in both structural and evolutionary terms. Some functions excel at the expense of others and many species have evolved an optimal balance between feather micro-structure and behavioral patterns that suit their specific environment. Several relationships between feather function and the structural properties of water bird feathers can be identified as specific evolutionary adaptations.

Part of the book: Birds