The structure and functions of the contour feathers of water birds revisited

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.