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Re: Cormorants, anhingas & soaked feathers

There is a paper on this very topic in a recent issue of *Journal of Avian Biology* :

David Grémillet, Christophe Chauvin, Rory P. Wilson, Yvon Le Maho, Sarah Wanless
Unusual feather structure allows partial plumage wettability in diving great cormorants Phalacrocorax carbo
Journal of Avian Biology 36:57-63.

"The great cormorant Phalacrocorax carbo is thought to have a wettable plumage, providing low body insulation during foraging. Great cormorants should thus be constrained by water temperatures, and show high energy requirements. Surprisingly, this species has one of the widest breeding distributions of all diving birds, and does not require more food than these other species. We explored this apparent paradox by comparing the insulative properties of body plumage in four subspecies of great cormorants ranging from tropical to polar regions. We found that all subspecies retained an insulating air layer in their plumage, which was, however, much thinner than for other species of diving birds. Detailed examination of the plumage showed that each cormorant body feather has a loose, instantaneously wet, outer section and a highly waterproof central portion. This indicates that the plumage of great cormorants is only partly wettable, and that birds maintain a thin layer of air in their plumage. Our findings suggest an unusual morphological-functional adaptation to diving which balances the antagonist constraints of thermoregulation and buoyancy."

In brief, cormorants sacrifice some insulation but gain better maneuvrability, important in a group of birds that catch fish mostly by active hunting near the bottom.
Probably something similar applies to anhingas, they fish quite differently from cormorants (spearing) but have a unique ability to regulate their buoyancy with high precision (an anhinga can sink until just the bill protrudes and then "re-float" itself, both without moving). This would probably be impossible with a large and probably not completely controllable amount of air in the plumage.

Tommy Tyrberg