The Gadwall (Chaulelasmus streperus) is a widely distributed duck, appearing throughout Europe and N. America, as well as in Asia and the north of Africa. It is a freshwater species, remarkable for the great development of the comb-like ‘teeth’ at the margin of the bill. It is 19-20 inches long, generally grayish, finely mottled, with chestnut wing coverts. The underside of the wing pure white, while the speculum of the drake is blue.
John H. Finley ed. Nelson's Perpetual Loose-Leaf Encyclopaedia (vol. 5) (New York, NY: Thomas Nelson and Sons, 1917)