Photo of the Week - January 2, 2013

Double-crested Cormorant pair
perching and drying wings.
Phalacrocorax auritus

Capitol Lake
Olympia, WA
January 2, 2013

Cormorants are among the most easily recognizable birds. Their tall bodies, black silhouettes and long necks are easy to spot. It is their wing-drying posture that makes them so quickly identifiable. In an essay on spread-wing postures, Paul R. Ehrlich, David S. Dobkin, and Darryl Wheye state that Cormorants use spread-wing postures for drying their wings.

"The structure of cormorant and Anhinga feathers decreases buoyancy and thus facilitates underwater pursuit of fishes. Hence their plumage is not water-repellent, but "wettable." It has been suggested that the function of the spread-wing postures in these birds is to dry the wings after wetting. Biologists once thought that deficient production of oils from the preen gland necessitate wing-drying behaviors. We now know, however, that the degree of waterproofing of feathers is primarily due to their microscopic structure, not to their being oiled. In addition to helping wing feathers to dry, other suggested functions for these postures include regulating body temperature ("thermoregulation"), realigning of feathers, forcing parasites into motion to ease their removal, and helping the perched bird to balance."