The Contour Feathers of Cisticolae: Adaptations to Annual Rainfall | Chapter 3 | Geography, Earth Science and Environment: Research Highlights Vol. 7

This study has shown for the first time a correlation between the feather microstructure of land birds and the annual rainfall of their habitats that is shaped by the evolutionary forces of water repellency and resistance to water penetration. Birds of the genus Cisticola occur over most of Southern Africa in varying habitats ranging from low to high altitudes and wet to dry areas causing species to have unique distributions. In order to determine if Cisticolas have evolved species‐specific water repellency and resistance to water penetration compatible with their habitats, we have measured the barb diameter and spacing of abdominal, breast and throat feathers of six cisticola species and related the results to mean annual rainfall and altitudes in five different locations. Water repellency was not significantly associated with altitude or maximum mean summer temperatures. However, water repellency increased markedly with annual rainfall in the 550 to 600 mm/year range for abdominal and breast feathers, but not for throat feathers. This increase was evident both among species occurring at multiple sites and among different species occurring at single sites. Food sources too will change with higher or lower rainfall. If climate change involves access to open water, further changes in feather structure may be expected such as presently seen in Dippers and shorebirds. However, the two species occurring at the wettest sites showed low water repellency, but increased resistance to water penetration. These findings suggest that water repellency and resistance to water penetration are part of the evolutionary forces that shape the microstructure of Cisticola contour feathers.

Small changes in ramus width and spacing can alter a mostly water-repellent structure into one that is water resistant and vice versa. This feature represents a highly adaptive trait in the evolution of contour feathers for it enabled birds to colonize specific habitats and adopt specialized feeding habits.

 

Author (s) Details

 

Jana le Roux Klem
Research Unit, Environmental Sciences and Management, North-West University, Potchefstroom, South Africa.

 

Hindrik Bouwman
Research Unit, Environmental Sciences and Management, North-West University, Potchefstroom, South Africa.

 

Arie M. Rijke
University of Virginia, Charlottesville, Virginia, United States.

 

Please see the book here:- https://doi.org/10.9734/bpi/geserh/v7/4441

Physical Principles of Water Penetration and Repellency of Porous Surfaces and their Relevance to Feathers | Chapter 2 | Geography, Earth Science and Environment: Research Highlights Vol. 7

The present study highlights water penetration and repellency of feathers and these factors’ relation to bird behavior and habitat in light of information that has become available since 1985. We present the physical principles of water penetration and repellency of porous surfaces and their relevance to feathers. The study shows that the requirements for water repellency of feathers and those for resistance to water penetration are partly in conflict with each other. 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. Both aspects can be presented and evaluated by the same parameter, expressed in terms of the width 2r and spacing 2d of the barbs, (r + d)/r. This parameter is small for water birds, particularly for those that dive frequently and are concerned with water penetration. It is larger for terrestrial birds, which are concerned primarily with water repellency. In each family of water birds, with some exceptions, a balance between water repellency and resistance to penetration exists as an adaptation to their particular habitat and behavioral pattern. For example, we discuss the habit of cormorants and darters of spreading their wings after a period in the water in relation to the value of the parameter. We postulate that information on habitat and behavior and, indirectly, the family identity of water birds, including those of fossil taxa, can be inferred from this parameter. It is likely that many more examples of contour-feather structure correlating with specific behavior or habitat will be found once more data have been gathered. However, the above examples suffice to suggest that each feather substructure represents an evolutionary adaptation to a specific set of behavioral patterns and habitat conditions.

 

Author (s) Details

 

Arie M. Rijke
Department of Materials Science and Engineering, University of Virginia, 116 Engineer's Way, P. O. Box 400745, Charlottesville VA 22904-4745, USA.

 

William A. Jesser
Department of Materials Science and Engineering, University of Virginia, 116 Engineer's Way, P. O. Box 400745, Charlottesville VA 22904-4745, USA.

 

Please see the book here:- https://doi.org/10.9734/bpi/geserh/v7/4443