It is commonly thought that anhingas perch on logs or tree branches to air dry their wings because the oil produced by their preen gland is insufficient to make their feathers waterproof. That has been shown to be an erroneous assumption.
Because the structure of the anhinga's feathers decreases buoyancy, allowing them to sink underwater and chase fish, the feathers become waterlogged. Once out of the water, the anhinga must dry their wings in order to function properly.
"We know now, 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 [spread wings, perching] include regulating body temperature [...], realigning of feathers, forcing parasites into motion to ease their removal, and helping the perched bird to balance."
[The above from an article by Paul R. Ehrlich, et. al.]
Photo by Lois Anne.
