Cormorants

About 40 species of coastal and freshwater divers, recently split among several genera. They pursue fish underwater, propelled by the feet, and their plumage wets deliberately: reduced waterproofing lowers buoyancy and makes diving cheaper, at the cost of long spells spent drying with the wings held open. The bill is hooked at the tip for gripping fish. Most nest colonially, and their guano has been harvested commercially for centuries.