244 NATATORES. 



sient visitors in the spring and autumn months, the 

 cold regions of the fur countries being their usual 

 place of resort during Summer. 



The Canvass-back is the famous Duck which is 

 generally considered by epicures as the finest of all 

 the Duck family, — its flesh being thought to possess 

 a peculiarly agreeable flavor, which no other fowl can 

 claim. The most common winter resort of these cele- 

 brated Ducks is the Chesapeake Bay and the rivers 

 and streams belonging to it, such as the Susquehanna, 

 Patapsco, Potomac, and James rivers. Here they 

 sometimes assemble in flocks of such great numbers 

 as to cover the surface of the water for acres in ex- 

 tent, and when they rise suddenly the noise of their 

 wings resembles thunder. The abundance of their 

 favorite food (a species of Valisneria), a grass-like 

 plant which grows to the height of a few feet above 

 tJie water, the roots of which seem to form their main 

 sustenance, is evidently the great attraction for these 

 birds, as of later years their numbers appear to have 

 decreased, while at the same time the plant has be- 

 come less abundant. These Ducks are often seen 

 feeding in company with several other species, such 

 as the Black-headed Duck, the Widgeon and the Ked- 

 headed Duck. They all appear to live upon the same 

 plant; the Canvass-back and the Black-head diving 

 to obtain the roots, while the Widgeon and the Red- 

 head prefer the leaves. The Canvass-back has also 

 been found on the waters of the Hudson, and upon 

 Bome of the western rivers; but its chief winter 



