BIRDS OF PENNSYLVANIA. 13 



ulum bluish-gray, lighter externally ; the innermost secondaries of the speculum 

 edged externally with black ; iris red ; feet grayish-blue. 



Female with the black and chestnut replaced by brown, the cheeks and chin 

 lighter, and some tinged with dull-rufous. 



Length, 20. 10 inches; wing, 9.30; tarsus, 1.70; commissure, 2.65 inches. 



Flab. Nearly all of North America, breeding from the north-western States north- 

 ward to Alaska. 



Wilson, in describing the habits of the Canvas-back, says : " The 

 Canvas-back Duck arrives in the United States from the north about 

 the middle of October : a few descend to the Hudson and Delaware ; 

 but the great body of these birds resort to the numerous rivers be- 

 longing to and in the neighborhood of the Chesapeake Bay, particu- 

 larly the Susquehanna, the Patapsco, Potomac and James rivers, which 

 appear to be their general winter rendezvous. Beyond this, to the 

 south, I can find no certain accounts of them. At the Susquehanna, 

 they are called Canvas-backs ; on the Potomac. White-backs ; and on 

 James river, Sheldrakes. They are seldom found at a great distance 

 up any of these rivers, or even in the salt-water bay, but in that par- 

 ticular part of tide-water where a certain grass-like plant grows, on 

 the roots of which they feed. This plant, which is said to be a spe- 

 cies of Vallisneria, grows on fresh-water shoals of from seven to nine 

 feet (but never where these are occasionally dry), in long, narrow, 

 grass-like blades, of four or five feet in length ; the root is white, and 

 has some resemblance to small celery. This grass is in many places 

 so thick that a boat can with difficulty be rowed through it, it so im- 

 pedes the oars. The shores are lined with large quantities of it, torn 

 up by the Ducks, and drifted up by the winds, lying, like hay, in 

 windrows. Wherever this plant grows in abundance, the Canvas- 

 backs may be expected either to pay occasional visits or to make it 

 their regular residence during the winter. It occurs in some parts of 

 the Hudson ; in the Delaware, near Gloucester, a few miles below 

 Philadelphia ; and in most of the rivers that fall into the Chesapeake, 

 to each of which particular places these Ducks resort; while, in waters 

 unprovided with this nutritive plant, they are altogether unknown. 



" On the first arrival of these birds in the Susquehanna, near Havre- 

 de-Grace, they are generally lean ; but such is the abundance of their 

 favorite food that, towards the beginning of November, they are in 

 pretty good order. They are excellent divers, and swim with great 

 speed and agility. They sometimes assemble in such multitudes as 

 to cover several acres of the river, and, when they rise suddenly, pro- 

 duce a noise resembling thunder. They float about these shoals, div- 

 ing, and tearing up the grass by the roots, which is the only part they 

 eat. They are extremely shy, and can rarely be approached, unless 

 by stratagem. When wounded in the wing, they dive to such pro- 

 digious distances, and with such rapidity, continuing it so persever- 



